[LoopVectorize] Vectorize the reduction pattern of integer min/max with index.

[Mel-Chen]

Summary

The Concept and Approach

Here is an example of min max with index pattern:

int idx = ii;
int max = mm;
for (int i = 0; i < n; ++i) {
  int x = a[i];
  if (max < x) {
    max = x;
    idx = i;
  }
}

After transfering to LLVM IR, it will look like this:

define i64 @smax_idx(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
entry:
  br label %for.body

for.body:
  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
  %0 = load i64, ptr %arrayidx
  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
  %cmp1 = icmp slt i64 %max.09, %0
  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
  br i1 %exitcond.not, label %exit, label %for.body

exit:
  store i64 %1, ptr %res_max
  ret i64 %spec.select7
}

Then we'll make a def-use graph for illustration (focus on for.body):

                   ┌──────────────────┐
                   ▼                  │
          %indvars.iv                 │
         /         │ \                │
        ▼          │  ▼               │
%arrayidx          │%indvars.iv.next  │
     │             │      │        └──┘
     ▼             │      ▼
    %0             │   %exitcond.not
┌─┐ /└───────────┐ │      │
│ ▼▼             │ │      ▼
│ %1             │ │      br
│  │             │ │
│  ▼             │ │
│phi_max:%max.09 │ │
└──┘  \    ┌─────┘ │
       ▼   ▼       │ 
       %cmp1       │
      ┌─┐ \        │
      │ ▼  ▼       ▼
      │ %spec.select7
      │       │
      │       ▼
      │    phi_idx:%idx.011 
      └───────┘

Generally, we will do traveling that starts from the phi of the loop header block when recognizing a reduction pattern, that is, phi_max and phi_idx in the graph. Taking simple max reduction as an example, we will start with phi_max and perform depth-first traveling on the def-use graph to check whether we can go back to phi_max, which means forming a cycle. Besides that, two things must be confirmed: ​​first, at least one reduction operation, the operations in the cycle, is used outside the loop. If there is no external user, there is no need for the vectorizer to vectorize for it. Second, the reduction operation cannot have users inside the loop, unless the internal users are also reduction operations, and this is one of the issues that this patch needs to handle.

Let’s go back to the def-use graph. If we want to find two cycles for one traveling, it is obviously difficult. Besides making the algorithm more complicated, we also face the issue of ordering phi_max and phi_idx, because we cannot control the order of input IR. The better way is to find the cycles of phi_max and phi_idx respectively according to the original algorithm, and perform the second stage - combining phi_max and phi_idx. In this way, the phi order issue can be solved.

for.body:
  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
…

And 

for.body:
  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
…

Next, let's see what type of cycle phi_max and phi_idx are. Ignoring the edge (phi_max, %cmp1), phi_max is the general max reduction, and phi_idx is the select-cmp reduction. In other words, we need to recognize max reduction and select-cmp reduction in the first stage of reduction recognition. Then use the relationship between the two reductions found in the first stage to perform the combination in the second stage.

After the recognition is completed, the next step is code generation. First, let's look at how to code generation when there is no dependency between max reduction and select-cmp reduction (that is, when it is not a pattern of min max with index):

/* Normal two independent reductions*/
int idx = ii;
int max = mm;
for (int i = 0; i < n; ++i) {
  int x = a[i];
  if (max < x) 
    max = x; 
  if (b[i] < a[i])
    idx = i;
}

vec_max = broadcast(mm)
vec_step = iota
vec_idx = broadcast(MIN_VALUE(DType))
for (int i = 0; i < n; i += vf) {
  vec_a = load(a, i, vf)
  vec_b = load(b, i, vf)
  vec_cmp = vec_b < vec_a
  vec_max = max(vec_max, vec_a)
  vec_idx = select(vec_cmp, vec_step, vec_idx)
  vec_step += vf;
}
red_max = reduce_max(vec_max)
red_idx_candidate = reduce_max(vec_idx)
red_idx = red_idx_candidate == MIN_VALUE(DType) ? ii : red_idx_candidate

And when there is a dependency between max reduction and select-cmp reduction (that is, it is a pattern of min max with index), what will happen to code generation?

/* Two dependent reductions, the max with first index pattern */
int idx = ii;
int max = mm;
for (int i = 0; i < n; ++i) {
  int x = a[i];
  if (max < x) {  // strict
    max = x; 
    idx = i;
  }
}

vec_max = broadcast(mm)
vec_step = iota
vec_idx = broadcast(MIN_VALUE(DType))
for (int i = 0; i < n; i += vf) {
  vec_a = load(a, i, vf)
  vec_cmp = vec_max < vec_a
  vec_max = max(vec_max, vec_a)
  vec_idx = select(vec_cmp, vec_step, vec_idx)
  vec_step += vf;
}
red_max = reduce_max(vec_max)
vec_all_max = broadcast(red_max)
mask = (vec_max == vec_all_max)
red_idx_candidate = reduce_min(vec_idx, mask)  // since this case is strict max reduction
red_idx = red_idx_candidate == MIN_VALUE(DType) ? ii : red_idx_candidate

The biggest difference is whether a mask needs to be created between max reduction and select-cmp reduction in the exit block (or middle block in LLVM vectorizer). Secondly, according to whether min max is strict or non-strict, decide whether to use the maximum index or the minimum index. Therefore, as long as the correct reduction dependency can be established in the recognition stage, and do code generation according to the dependency, the pattern of min max with index can be vectorized.

The Implementation in LLVM

According to the description in the previous chapter, first of all, the vectorizer must be able to recognize select-cmp reduction. Next, we need to solve the issue of internal reduction users, so that min max reduction can accept loop internal users in the first recognition stage. The third is to combine min max reduction and select-cmp reduction. Finally, according to the relationship between select-cmp reduction and min max reduction, a mask is generated in the middle block and reduction fix is performed.

Select-Cmp Reduction

At present, there is already a select-cmp implementation in LLVM, developed by the author david-arm. However, the current implementation restricts the value of non-reduction phi to be loop invariant, which does not meet our demands. Therefore, we need to expand this feature, namely SelectIVICmp/ SelectIVFCmp.
Taking SelectIVICmp as an example, the result of vectorization is as follows:

/* A SelectIVICmp example */
#include <stdint.h>

int64_t idx_scalar(int64_t *a, int64_t *b, int64_t ii, int64_t n) {
  int64_t idx = ii;
  for (int64_t i = 0; i < n; ++i)
    idx = (a[i] > b[i]) ? i : idx;

  return idx;
}

/* LLVM IR for vectorized SelectIVICmp reduction */
define dso_local i64 @idx_scalar(ptr nocapture noundef readonly %a, ptr nocapture noundef readonly %b, i64 noundef %ii, i64 noundef %n) local_unnamed_addr #0 {
…

vector.body:                                      ; preds = %vector.body, %vector.ph
  %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
  %vec.ind = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, %vector.ph ], [ %vec.ind.next, %vector.body ]
  %vec.phi = phi <4 x i64> [ <i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808>, %vector.ph ], [ %6, %vector.body ]
  %0 = add i64 %index, 0
  %1 = getelementptr inbounds i64, ptr %a, i64 %0
  %2 = getelementptr inbounds i64, ptr %1, i32 0
  %wide.load = load <4 x i64>, ptr %2, align 8, !tbaa !4
  %3 = getelementptr inbounds i64, ptr %b, i64 %0
  %4 = getelementptr inbounds i64, ptr %3, i32 0
  %wide.load1 = load <4 x i64>, ptr %4, align 8, !tbaa !4
  %5 = icmp sgt <4 x i64> %wide.load, %wide.load1
  %6 = select <4 x i1> %5, <4 x i64> %vec.ind, <4 x i64> %vec.phi
  %index.next = add nuw i64 %index, 4
  %vec.ind.next = add <4 x i64> %vec.ind, <i64 4, i64 4, i64 4, i64 4>
  %7 = icmp eq i64 %index.next, %n.vec
  br i1 %7, label %middle.block, label %vector.body, !llvm.loop !8

middle.block:                                     ; preds = %vector.body
  %8 = call i64 @llvm.vector.reduce.smax.v4i64(<4 x i64> %6)
  %rdx.select.cmp = icmp ne i64 %8, -9223372036854775808
  %rdx.select = select i1 %rdx.select.cmp, i64 %8, i64 %ii
  %cmp.n = icmp eq i64 %n, %n.vec
  br i1 %cmp.n, label %for.exit.loopexit, label %scalar.ph
…
}

Assuming that the format of the induction variable i is {start, +, step}, SelectIVICmp should use start - step as its identity. However, for easy implementation, I directly use MIN_VALUE(DType) as identity (-9223372036854775808 in above example). The role of identity here is the sentinel value, which represents the start value of SelectIVICmp (%ii in the above example). In the end, if the result of reduce_max is identity, the result of reduction will be fixed as the start value.

Note that this is a temporary implementation. Unexpected errors may occur when the start of the induction variable is MIN_TYPE(DType), or when the maximum value of the induction variable exceeds SignedMax(DType). Generally, it should be implemented by two reductions.

Internal User Issue: UserRecurPhi and UserRecurKind

I modified the function isMinMaxPattern so that while identifying min max reduction, it is also possible to identify whether there is an index pattern that may depend on min max reduction.

isMinMaxIdxPattern will set UserRecurPhi and UserRecurKind according to the current select and cmp IR traveling, and the currently recognizing kind of min max reduction. Please refer to the form below:

Take the first example:
  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
  %cmp1 = icmp slt i64 %max.09, %0
  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011

cmp format	%max.09 < %0	%max.09 <= %0	%max.09 > %0	%max.09 >= %0	%0 < %max.09	%0 <= %max.09	%0 > %max.09	%0 >= %max.09
UMax SMax	UserRecurPhi=select.getFalseValue() UserRecurKind=MinMaxFirstIdx	UserRecurPhi=select.getFalseValue() UserRecurKind=MinMaxLastIdx	UserRecurPhi=select.getTrueValue() UserRecurKind=MinMaxLastIdx	UserRecurPhi=select.getTrueValue() UserRecurKind=MinMaxFirstIdx	UserRecurPhi=select.getTrueValue() UserRecurKind=MinMaxLastIdx	UserRecurPhi=select.getTrueValue() UserRecurKind=MinMaxFirstIdx	UserRecurPhi=select.getFalseValue() UserRecurKind=MinMaxFirstIdx	UserRecurPhi=select.getFalseValue() UserRecurKind=MinMaxLastIdx
UMin SMin	UserRecurPhi=select.getTrueValue() UserRecurKind=MinMaxLastIdx	UserRecurPhi=select.getTrueValue() UserRecurKind=MinMaxFirstIdx	UserRecurPhi=select.getFalseValue() UserRecurKind=MinMaxFirstIdx	UserRecurPhi=select.getFalseValue() UserRecurKind=MinMaxLastIdx	UserRecurPhi=select.getFalseValue() UserRecurKind=MinMaxFirstIdx	UserRecurPhi=select.getFalseValue() UserRecurKind=MinMaxLastIdx	UserRecurPhi=select.getTrueValue() UserRecurKind=MinMaxLastIdx	UserRecurPhi=select.getTrueValue() UserRecurKind=MinMaxFirstIdx

According to this table, UserRecurPhi will be set to %idx.011 (FalseValue in the select IR) and UserRecurKind to MinMaxFirstIdx.

Once UserRecurPhi is set, it means that the select should belong to another unknown reduction, UserRecurPhi should be the phi of the unknown reduction, and UserRecurKind is the expected reduction kind. Both UserRecurPhi and UserRecurKind will be used in the second phase recognition.

The Second Phase of Recognition

At the end of function canVectorizeInstrs, there will be a second confirmation against the reduction that has UserRecurPhi.
At this stage, all reductions should have been found. At this point, the vectorizer only needs to check whether UserRecurPhi is a reduction phi. At the same time, by using the function fixUserRecurrence, the SelectIVICmp will be converted into MinMaxFirstIdx or MinMaxLastIdx according to UserRecurKind.

Code Generation and Reduction Fix

Min max with index vectorization does not need to be adjusted for the contents of vector.body, but requires changes in function fixReduction.

We must ensure that min max reduction is fixed earlier than index reduction, because index reduction needs to use the mask generated by min max reduction. We can achieve this by modifying the function fixCrossIterationPHIs. The map DependRecurrenceMasks will keep the mask generated by min max reduction. If the mask required by index reduction is not ready, it will postpone the fix of the index reduction until the required mask is ready.

---

Consider the following loops:

int idx = ii;
int max = mm;
for (int i = 0; i < n; ++i) {
  int x = a[i];
  if (max < x) {
    max = x;
    idx = i;
  }
}

and

int idx = ii;
int max = mm;
for (int i = 0; i < n; ++i) {
  int x = a[i];
  if (max <= x) {
    max = x;
    idx = i;
  }
}

Changes:

• New recurrence Kinds: MinMaxFirstIdx and MinMaxLastIdx. This kind is not directly generated by function AddReductionVar, but converted from SelectIVICmp/SelectIVFCmp.

TODOs:

• Now have not support that the min/max recurrence without exit instruction. Refer to test case smax_idx_max_no_exit_user.
• Support the min/max recurrence in select(cmp()). Refer to test case smax_idx_select_cmp.
• Support FP min/max recurrence.

[Mel-Chen]

Rebase and update the command in test case.

[Mel-Chen]

Changes:

• Fix interleave code generation for SelectIVICmp and SelectIVFCmp.
• Fix the internal compiler error for MinMaxFirstIdx and MinMaxLastIdx when -force-vector-width=1.
• Update test cases. Add more run command lines.

[Mel-Chen]

Changes:

• Rebase
• Split the patch of test case and implementation
• Update FIXME

[Mel-Chen]

Changes:

• Remove function createInductionSelectCmpTargetReduction
• Add function createSentinelValueHandling
• Fix the start value of SelectCmp and MinMaxIdx

And then I don't know why all FIXME has been fixed, will confirm.

[Mel-Chen]

Rebase and fix the check prefix in test cases.

[Mel-Chen]

Changes:

• Confirm the operands of intrinsic and cmp. Fixed test case @smax_idx_not_vec_1.
• Format code.

[Mel-Chen]

Rebase.

[Mel-Chen]

@fhahn Ping. What do you think of my approach? I am looking forward to your reply.

[Mel-Chen]

Changes:

• Rebase
• Fix the bug of predicate normalization

[Mel-Chen]

Rebase and update test case result.

[fhahn]

llvm/include/llvm/Analysis/IVDescriptors.h

379

It would be helpful to document how the new system of recurrences depending on other recurrences would work I think, possibly also with an explanation of the whole approach in the patch description.

llvm/lib/Analysis/IVDescriptors.cpp

703

nit: Variables should start with upper case

also, move definition to use?

728

The naming here is a bit confusing now, NonPhi can be an increasing loop induction? In that case it would be a phi, right?

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

754

We are in the process of removing those kinds of global maps that are used to carry information used during codegen and later. Ideally the combination of values would be modeled explicitly in the exit block of the plan, but we are not there yet. This is the main reason for D132063 doing things the way it does.

3768

this would need documenting.

llvm/test/Transforms/LoopVectorize/smax-idx.ll

2

Could you add new tests as a separate patch?

[Mel-Chen]

llvm/include/llvm/Analysis/IVDescriptors.h

379

Sure. I will document the whole approach. and update in the summary tomorrow.
Quickly explain the function of UserRecurPhi . The purpose of UserRecurPhi is to allow the recurrence to be used in the loop (loop internal use), and to ensure that the user is also a recurrence. UserRecurPhi will record the candidate user recurrence phi, and UserRecurKind will recored the excepted user recurrence kind. Currently I'm limiting candidates to one, but it should be possible to have more than one.

llvm/lib/Analysis/IVDescriptors.cpp

728

Yes, it's a little confusing here. It could be better to replace NonPhi with NonRecurPhi. By the way, are you interested in supporting full functional SelectCmp pattern? I think min max with index pattern really needs to depend on the SelectCmp to be safe.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

754

I see., but DependRecurrenceMasks exists for a reason. Consider the following case:

int idx = ii;
int foo = jj;
int max = mm;
for (int i = 0; i < n; ++i) {
  int x = a[i];
  if (max < x) {
    max = x;
    idx = i;
    foo = b[i];
  }
}

That mask has the chance to be reused, and I try to keep that flexibility. Of course, we can recalculate the mask for each reduction that needs a mask, but currently using the global maps to preserve the mask is a relatively simple method that I think of.
I have heard that VPlan is going to be extended to other blocks, could you share the relevant discussion links?

3768

Sure. Quick explanation: min/max recurrence should be done earlier than min max idx recurrence, because idx recurrence depends on the mask produced by min max recurrence. Here is to ensure that the recurrence dependencies are correct.

llvm/test/Transforms/LoopVectorize/smax-idx.ll

2

Of course. I will split an NFC patch tomorrow.

[Mel-Chen]

Split test case into parent revision.

[Mel-Chen]

llvm/include/llvm/Analysis/IVDescriptors.h

379

Too busy today. The document will be available in next week.

[Mel-Chen]

@fhahn Updated my approach introduction in the summary.
If you have any questions, please contact me. Looking forward to discussing with you again. Thank you.

[Mel-Chen]

@fhahn Ping. I'd be glad to discuss this patch with you.

[fhahn]

llvm/lib/Analysis/IVDescriptors.cpp

711

Using this API seems unnecessarily strict; we don't need to bounds (and getBounds may fail if It cannot identify the bounds), we just need to check the direction of the IV, which can be done by checking if it is an induction PHI and use SE.getMonotonicPredicateTyp.

llvm/test/Transforms/LoopVectorize/select-min-index.ll

135–136

Is this incorrectly vectorized or does the test name need fixing? It looks like %min.val isn't an actual minimum value phi?

[Mel-Chen]

Rebase this patch, and created revision D149731 to preserving min max operation in select-cmp form.

[Mel-Chen]

Changes:

• Split SelectIVICmp and SelectIVFCmp out
• Add Comment
• Minor refine the code

[Mel-Chen]

Changes:

• Format and minor fix

[artagnon]

llvm/lib/Analysis/IVDescriptors.cpp

415

Why?

424–426

If you separate out the MinMaxIdx pattern into its own function, we can check NumCmpSelectPatternInst for it separately.

831–860

This is a bit cryptic: would you consider adding more RecurKinds to make this less cryptic?

877–878

Can we avoid the expensive call to isInductionPHI() by checking that the SCEVAddRec is a SCEVConstant?

1306–1313

Why not merge this with the RecurKind::SMax case?

1341–1342

Rename these to IMinMaxFirstIdx and IMinMaxLastIdx?

llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp

881

Typo: comfirm.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

4051–4054

RdxDesc.isOrdered() can help you pick between FCMP_OEQ and FCMP_UEQ.

[shiva0217]

llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp

892

Instead of fixUserRecurrence to setDependMinMaxRecurDes and change the user RecurKind, is it possible to setDependMinMaxRecurDes when isReductionPHI return true?

If we able to propagate parent(dependent) RecurDes to isReductionPHI, perhaps we can create reduction as following.

RecurKind ParentKind = RedDes.getRecurrenceKind();
if (ParentKind == RecurKind::SMax) {
  if (AddReductionVar(Phi, RecurKind::MinMaxFirstIdx, TheLoop, FMF, RedDes, DB, AC, DT,
                      SE)) {
    LLVM_DEBUG(dbgs() << "Found an MinMaxFirstIdx reduction PHI." << *Phi << "\n");
    return true;
  }
}

The dependency for the RecurKind could be explicitly and avoid the user RecurKind fixup.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

3768

Perhaps we could do the sorting according to the reduction dependency before calling fixReduction which may be similar to https://reviews.llvm.org/D157631.

4023

Should we check isMinMaxRecurrenceKind(Kind) and isMinMaxIdxRecurrenceKind for user kind?

Although it would be the only dependency currently, it might be explicit for the reader and avoid unexpected codegen in the future.

4025

Could we encapsulate the mask generation to createMinMaxIdxMaskOp or other name you prefer?

4047

Should we check isMinMaxRecurrenceKind(Kind) and isMinMaxIdxRecurrenceKind for user kind?

4048

Could we encapsulate the mask generation to createMinMaxIdxMask or similar?

llvm/include/llvm/Analysis/IVDescriptors.h

 class Loop;
 class PredicatedScalarEvolution;
 class ScalarEvolution;
 class SCEV;
 class StoreInst;
 
 /// These are the kinds of recurrences that we support.
 enum class RecurKind {
-  None,       ///< Not a recurrence.
-  Add,        ///< Sum of integers.
-  Mul,        ///< Product of integers.
-  Or,         ///< Bitwise or logical OR of integers.
-  And,        ///< Bitwise or logical AND of integers.
-  Xor,        ///< Bitwise or logical XOR of integers.
-  SMin,       ///< Signed integer min implemented in terms of select(cmp()).
-  SMax,       ///< Signed integer max implemented in terms of select(cmp()).
-  UMin,       ///< Unisgned integer min implemented in terms of select(cmp()).
-  UMax,       ///< Unsigned integer max implemented in terms of select(cmp()).
-  FAdd,       ///< Sum of floats.
-  FMul,       ///< Product of floats.
-  FMin,       ///< FP min implemented in terms of select(cmp()).
-  FMax,       ///< FP max implemented in terms of select(cmp()).
-  FMulAdd,    ///< Fused multiply-add of floats (a * b + c).
-  SelectICmp, ///< Integer select(icmp(),x,y) where one of (x,y) is loop
+  None,         ///< Not a recurrence.
+  Add,          ///< Sum of integers.
+  Mul,          ///< Product of integers.
+  Or,           ///< Bitwise or logical OR of integers.
+  And,          ///< Bitwise or logical AND of integers.
+  Xor,          ///< Bitwise or logical XOR of integers.
+  SMin,         ///< Signed integer min implemented in terms of select(cmp()).
+  SMax,         ///< Signed integer max implemented in terms of select(cmp()).
+  UMin,         ///< Unisgned integer min implemented in terms of select(cmp()).
+  UMax,         ///< Unsigned integer max implemented in terms of select(cmp()).
+  FAdd,         ///< Sum of floats.
+  FMul,         ///< Product of floats.
+  FMin,         ///< FP min implemented in terms of select(cmp()).
+  FMax,         ///< FP max implemented in terms of select(cmp()).
+  FMulAdd,      ///< Fused multiply-add of floats (a * b + c).
+  SelectICmp,   ///< Integer select(icmp(),x,y) where one of (x,y) is loop
                 ///< invariant
-  SelectFCmp  ///< Integer select(fcmp(),x,y) where one of (x,y) is loop
+  SelectFCmp,   ///< Integer select(fcmp(),x,y) where one of (x,y) is loop
                 ///< invariant
+  SelectIVICmp, ///< Integer select(icmp(),x,y) where one of (x,y) is increasing
+                ///< loop induction PHI
+  SelectIVFCmp, ///< Integer select(fcmp(),x,y) where one of (x,y) is increasing
+                ///< loop induction PHI
+  MinMaxFirstIdx, ///< Min/Max with first index
+  MinMaxLastIdx   ///< Min/Max with last index
 };
 
 /// The RecurrenceDescriptor is used to identify recurrences variables in a
 /// loop. Reduction is a special case of recurrence that has uses of the
 /// recurrence variable outside the loop. The method isReductionPHI identifies
 /// reductions that are basic recurrences.
 ///
 /// Basic recurrences are defined as the summation, product, OR, AND, XOR, min,
 /// or max of a set of terms. For example: for(i=0; i<n; i++) { total +=
 /// array[i]; } is a summation of array elements. Basic recurrences are a
 /// special case of chains of recurrences (CR). See ScalarEvolution for CR
 /// references.
 
 /// This struct holds information about recurrence variables.
 class RecurrenceDescriptor {
 public:
   RecurrenceDescriptor() = default;
 
   RecurrenceDescriptor(Value *Start, Instruction *Exit, StoreInst *Store,
                        RecurKind K, FastMathFlags FMF, Instruction *ExactFP,
                        Type *RT, bool Signed, bool Ordered,
                        SmallPtrSetImpl<Instruction *> &CI,
-                       unsigned MinWidthCastToRecurTy)
+                       unsigned MinWidthCastToRecurTy, PHINode *UserRecurPhi,
+                       RecurKind UserRecurKind)
       : IntermediateStore(Store), StartValue(Start), LoopExitInstr(Exit),
         Kind(K), FMF(FMF), ExactFPMathInst(ExactFP), RecurrenceType(RT),
         IsSigned(Signed), IsOrdered(Ordered),
-        MinWidthCastToRecurrenceType(MinWidthCastToRecurTy) {
+        MinWidthCastToRecurrenceType(MinWidthCastToRecurTy),
+        UserRecurPhi(UserRecurPhi), UserRecurKind(UserRecurKind) {
     CastInsts.insert(CI.begin(), CI.end());
   }
 
   /// This POD struct holds information about a potential recurrence operation.
   class InstDesc {
   public:
     InstDesc(bool IsRecur, Instruction *I, Instruction *ExactFP = nullptr)
         : IsRecurrence(IsRecur), PatternLastInst(I),
           RecKind(RecurKind::None), ExactFPMathInst(ExactFP) {}
 
     InstDesc(Instruction *I, RecurKind K, Instruction *ExactFP = nullptr)
         : IsRecurrence(true), PatternLastInst(I), RecKind(K),
           ExactFPMathInst(ExactFP) {}
 
+    InstDesc(bool IsRecur, Instruction *I, PHINode *CandUserRecurPhi,
+             RecurKind CandUserRecurKind, Instruction *ExactFP = nullptr)
+        : IsRecurrence(IsRecur), PatternLastInst(I), RecKind(RecurKind::None),
+          CandUserRecurPhi(CandUserRecurPhi),
+          CandUserRecurKind(CandUserRecurKind), ExactFPMathInst(ExactFP) {}
+
     bool isRecurrence() const { return IsRecurrence; }
 
     bool needsExactFPMath() const { return ExactFPMathInst != nullptr; }
 
     Instruction *getExactFPMathInst() const { return ExactFPMathInst; }
 
     RecurKind getRecKind() const { return RecKind; }
 
     Instruction *getPatternInst() const { return PatternLastInst; }
 
+    PHINode *getCandUserRecurPhi() const { return CandUserRecurPhi; }
+
+    RecurKind getCandUserRecurKind() const { return CandUserRecurKind; }
+
+    bool isCandidateUser() const {
+      return getCandUserRecurPhi() && getCandUserRecurKind() != RecurKind::None;
+    }
+
   private:
     // Is this instruction a recurrence candidate.
     bool IsRecurrence;
     // The last instruction in a min/max pattern (select of the select(icmp())
     // pattern), or the current recurrence instruction otherwise.
     Instruction *PatternLastInst;
     // If this is a min/max pattern.
     RecurKind RecKind;
     // Recurrence does not allow floating-point reassociation.
     Instruction *ExactFPMathInst;
+    // This instruction may be the operation of another recurrence.
+    // Record potential recurrence phi.
+    PHINode *CandUserRecurPhi = nullptr;
+    // And expected recurrence kind.
+    RecurKind CandUserRecurKind = RecurKind::None;
   };
 
   /// Returns a struct describing if the instruction 'I' can be a recurrence
   /// variable of type 'Kind' for a Loop \p L and reduction PHI \p Phi.
   /// If the recurrence is a min/max pattern of select(icmp()) this function
   /// advances the instruction pointer 'I' from the compare instruction to the
   /// select instruction and stores this pointer in 'PatternLastInst' member of
   /// the returned struct.
   static InstDesc isRecurrenceInstr(Loop *L, PHINode *Phi, Instruction *I,
                                     RecurKind Kind, InstDesc &Prev,
-                                    FastMathFlags FuncFMF);
+                                    FastMathFlags FuncFMF, ScalarEvolution *SE);
 
   /// Returns true if instruction I has multiple uses in Insts
   static bool hasMultipleUsesOf(Instruction *I,
                                 SmallPtrSetImpl<Instruction *> &Insts,
                                 unsigned MaxNumUses);
 
   /// Returns true if all uses of the instruction I is within the Set.
   static bool areAllUsesIn(Instruction *I, SmallPtrSetImpl<Instruction *> &Set);
 
   /// Returns a struct describing if the instruction is a llvm.(s/u)(min/max),
   /// llvm.minnum/maxnum or a Select(ICmp(X, Y), X, Y) pair of instructions
   /// corresponding to a min(X, Y) or max(X, Y), matching the recurrence kind \p
   /// Kind. \p Prev specifies the description of an already processed select
   /// instruction, so its corresponding cmp can be matched to it.
   static InstDesc isMinMaxPattern(Instruction *I, RecurKind Kind,
-                                  const InstDesc &Prev);
+                                  const InstDesc &Prev, Loop *Loop,
+                                  PHINode *OrigPhi, ScalarEvolution *SE);
+
+  /// Returns RecurKind describing which min/max recurrence kind the instruction
+  /// \p I belongs to. Return RecurKind::None if instruction \p I is not matched
+  /// any of min/max recurrence kind. Unlike isMinMaxPattern, this function does
+  /// not limit exactly one use of cmp value.
+  static RecurKind isMinMaxOperation(Instruction *I);
+
+  static InstDesc isMinMaxIdxPattern(Loop *Loop, Instruction *I,
+                                     PHINode *MinMaxPhi, RecurKind MinMaxKind,
+                                     ScalarEvolution *SE);
 
   /// Returns a struct describing whether the instruction is either a
   ///   Select(ICmp(A, B), X, Y), or
   ///   Select(FCmp(A, B), X, Y)
   /// where one of (X, Y) is a loop invariant integer and the other is a PHI
   /// value. \p Prev specifies the description of an already processed select
   /// instruction, so its corresponding cmp can be matched to it.
   static InstDesc isSelectCmpPattern(Loop *Loop, PHINode *OrigPhi,
-                                     Instruction *I, InstDesc &Prev);
+                                     Instruction *I, InstDesc &Prev,
+                                     ScalarEvolution *SE);
 
   /// Returns a struct describing if the instruction is a
   /// Select(FCmp(X, Y), (Z = X op PHINode), PHINode) instruction pattern.
   static InstDesc isConditionalRdxPattern(RecurKind Kind, Instruction *I);
 
   /// Returns identity corresponding to the RecurrenceKind.
   Value *getRecurrenceIdentity(RecurKind K, Type *Tp, FastMathFlags FMF) const;
 
static bool isFPMinMaxRecurrenceKind(RecurKind Kind) {
     return Kind == RecurKind::FMin || Kind == RecurKind::FMax;
   }
 
   /// Returns true if the recurrence kind is any min/max kind.
   static bool isMinMaxRecurrenceKind(RecurKind Kind) {
     return isIntMinMaxRecurrenceKind(Kind) || isFPMinMaxRecurrenceKind(Kind);
   }
 
+  /// Returns true if the recurrence kind is a max kind.
+  static bool isMaxRecurrenceKind(RecurKind Kind) {
+    return Kind == RecurKind::UMax || Kind == RecurKind::SMax ||
+           Kind == RecurKind::FMax;
+  }
+
+  static bool isMinMaxIdxRecurrenceKind(RecurKind Kind) {
+    return Kind == RecurKind::MinMaxFirstIdx ||
+           Kind == RecurKind::MinMaxLastIdx;
+  }
+
   /// Returns true if the recurrence kind is of the form
   ///   select(cmp(),x,y) where one of (x,y) is loop invariant.
   static bool isSelectCmpRecurrenceKind(RecurKind Kind) {
-    return Kind == RecurKind::SelectICmp || Kind == RecurKind::SelectFCmp;
+    return Kind == RecurKind::SelectICmp || Kind == RecurKind::SelectFCmp ||
+           Kind == RecurKind::SelectIVICmp || Kind == RecurKind::SelectIVFCmp ||
+     isMinMaxIdxRecurrenceKind(Kind);
   }
 
   /// Returns the type of the recurrence. This type can be narrower than the
   /// actual type of the Phi if the recurrence has been type-promoted.
   Type *getRecurrenceType() const { return RecurrenceType; }
 
   /// Returns a reference to the instructions used for type-promoting the
   /// recurrence.
   const SmallPtrSet<Instruction *, 8> &getCastInsts() const { return CastInsts; }
 
+  PHINode *getUserRecurPhi() const { return UserRecurPhi; }
+
+  void setRecurKind(RecurKind K) {
+    assert((K != RecurKind::None) && "Unexpected recurrence kind.");
+    Kind = K;
+  }
+
+  void setDependMinMaxRecDes(RecurrenceDescriptor *MMRD) {
+    assert(isMinMaxRecurrenceKind(MMRD->getRecurrenceKind()) &&
+           "DependMinMaxRecDes must be a min/max recurrence.");
+    DependMinMaxRecDes = MMRD;
+  }
+
+  RecurrenceDescriptor *getDependMinMaxRecDes() const {
+    return DependMinMaxRecDes;
+  }
+
+  bool hasUserRecurrence() const {
+    return UserRecurPhi && UserRecurKind != RecurKind::None;
+  }
+
+  bool fixUserRecurrence(RecurrenceDescriptor &UserRedDes);
+
   /// Returns the minimum width used by the recurrence in bits.
   unsigned getMinWidthCastToRecurrenceTypeInBits() const {
     return MinWidthCastToRecurrenceType;
   }
 
   /// Returns true if all source operands of the recurrence are SExtInsts.
   bool isSigned() const { return IsSigned; }
 
private:
   // True if this recurrence can be treated as an in-order reduction.
   // Currently only a non-reassociative FAdd can be considered in-order,
   // if it is also the only FAdd in the PHI's use chain.
   bool IsOrdered = false;
   // Instructions used for type-promoting the recurrence.
   SmallPtrSet<Instruction *, 8> CastInsts;
   // The minimum width used by the recurrence.
   unsigned MinWidthCastToRecurrenceType;
+
+  PHINode *UserRecurPhi = nullptr;
+
+  RecurKind UserRecurKind = RecurKind::None;
+
+  RecurrenceDescriptor *DependMinMaxRecDes = nullptr;
 };
 
 /// A struct for saving information about induction variables.
 class InductionDescriptor {
 public:
   /// This enum represents the kinds of inductions that we support.
   enum InductionKind {
     IK_NoInduction,  ///< Not an induction variable.

llvm/include/llvm/Transforms/Utils/LoopUtils.h

 /// Fast-math-flags are propagated using the IRBuilder's setting.
 Value *createSimpleTargetReduction(IRBuilderBase &B,
                                    const TargetTransformInfo *TTI, Value *Src,
                                    RecurKind RdxKind);
 
 /// Create a target reduction of the given vector \p Src for a reduction of the
 /// kind RecurKind::SelectICmp or RecurKind::SelectFCmp. The reduction operation
 /// is described by \p Desc.
-Value *createSelectCmpTargetReduction(IRBuilderBase &B,
+Value *createInvariantSelectCmpTargetReduction(IRBuilderBase &B,
                                                const TargetTransformInfo *TTI,
                                                Value *Src,
                                                const RecurrenceDescriptor &Desc,
                                                PHINode *OrigPhi);
 
+/// Create a target reduction of the given vector \p Src for a reduction of the
+/// kind RecurKind::SelectIVICmp or RecurKind::SelectIVFCmp. The reduction
+/// operation is described by \p Desc.
+Value *createInductionSelectCmpTargetReduction(IRBuilderBase &B,
+                                               const TargetTransformInfo *TTI,
+                                               Value *Src,
+                                               const RecurrenceDescriptor &Desc,
+                                               PHINode *OrigPhi);
+
+Value *createMMISelectCmpTargetReduction(IRBuilderBase &Builder,
+                                         const TargetTransformInfo *TTI,
+                                         Value *Src,
+                                         const RecurrenceDescriptor &Desc,
+                                         PHINode *OrigPhi, Value *SrcMask);
+
+/// Create a target reduction of the given vector \p Src for a reduction of the
+/// kind RecurKind::SelectICmp or RecurKind::SelectFCmp. The reduction operation
+/// is described by \p Desc.
+Value *
+createSelectCmpTargetReduction(IRBuilderBase &B, const TargetTransformInfo *TTI,
+                               Value *Src, const RecurrenceDescriptor &Desc,
+                               PHINode *OrigPhi, Value *SrcMask = nullptr);
+
 /// Create a generic target reduction using a recurrence descriptor \p Desc
 /// The target is queried to determine if intrinsics or shuffle sequences are
 /// required to implement the reduction.
 /// Fast-math-flags are propagated using the RecurrenceDescriptor.
 Value *createTargetReduction(IRBuilderBase &B, const TargetTransformInfo *TTI,
                              const RecurrenceDescriptor &Desc, Value *Src,
-                             PHINode *OrigPhi = nullptr);
+                             PHINode *OrigPhi = nullptr,
+                             Value *SrcMask = nullptr);
 
 /// Create an ordered reduction intrinsic using the given recurrence
 /// descriptor \p Desc.
 Value *createOrderedReduction(IRBuilderBase &B,
                               const RecurrenceDescriptor &Desc, Value *Src,
                               Value *Start);
 
 /// Get the intersection (logical and) of all of the potential IR flags

llvm/lib/Analysis/IVDescriptors.cpp

bool RecurrenceDescriptor::isIntegerRecurrenceKind(RecurKind Kind) {
   case RecurKind::And:
   case RecurKind::Xor:
   case RecurKind::SMax:
   case RecurKind::SMin:
   case RecurKind::UMax:
   case RecurKind::UMin:
   case RecurKind::SelectICmp:
   case RecurKind::SelectFCmp:
+  case RecurKind::SelectIVICmp:
+  case RecurKind::SelectIVFCmp:
+  case RecurKind::MinMaxFirstIdx:
+  case RecurKind::MinMaxLastIdx:
     return true;
   }
   return false;
 }
 
 bool RecurrenceDescriptor::isFloatingPointRecurrenceKind(RecurKind Kind) {
   return (Kind != RecurKind::None) && !isIntegerRecurrenceKind(Kind);
 }
 
+bool RecurrenceDescriptor::fixUserRecurrence(RecurrenceDescriptor &UserRedDes) {
+  RecurKind UserCurrKind = UserRedDes.getRecurrenceKind();
+  assert((UserCurrKind != RecurKind::None) && "Unexpected recurrence kind.");
+
+  if (isMinMaxRecurrenceKind(Kind))
+    if (UserCurrKind == RecurKind::SelectIVICmp ||
+        UserCurrKind == RecurKind::SelectIVFCmp) {
+      UserRedDes.setRecurKind(UserRecurKind);
+      UserRedDes.setDependMinMaxRecDes(this);
+      return true;
+    }
+
+  return false;
+}
+
 /// Determines if Phi may have been type-promoted. If Phi has a single user
 /// that ANDs the Phi with a type mask, return the user. RT is updated to
 /// account for the narrower bit width represented by the mask, and the AND
 /// instruction is added to CI.
 static Instruction *lookThroughAnd(PHINode *Phi, Type *&RT,
                                    SmallPtrSetImpl<Instruction *> &Visited,
                                    SmallPtrSetImpl<Instruction *> &CI) {
   if (!Phi->hasOneUse())
bool RecurrenceDescriptor::AddReductionVar(
   bool FoundReduxOp = false;
 
   // We start with the PHI node and scan for all of the users of this
   // instruction. All users must be instructions that can be used as reduction
   // variables (such as ADD). We must have a single out-of-block user. The cycle
   // must include the original PHI.
   bool FoundStartPHI = false;
 
+  PHINode *UserRecurPHI = nullptr;
+  RecurKind UserRecurKind = RecurKind::None;
+
   // To recognize min/max patterns formed by a icmp select sequence, we store
   // the number of instruction we saw from the recognized min/max pattern,
   //  to make sure we only see exactly the two instructions.
   unsigned NumCmpSelectPatternInst = 0;
   InstDesc ReduxDesc(false, nullptr);
 
   // Data used for determining if the recurrence has been type-promoted.
   Type *RecurrenceType = Phi->getType();
if (!Cur->isCommutative() && !IsAPhi && !isa<SelectInst>(Cur) &&
         !VisitedInsts.count(dyn_cast<Instruction>(Cur->getOperand(0))))
       return false;
 
     // Any reduction instruction must be of one of the allowed kinds. We ignore
     // the starting value (the Phi or an AND instruction if the Phi has been
     // type-promoted).
     if (Cur != Start) {
       ReduxDesc =
-          isRecurrenceInstr(TheLoop, Phi, Cur, Kind, ReduxDesc, FuncFMF);
+          isRecurrenceInstr(TheLoop, Phi, Cur, Kind, ReduxDesc, FuncFMF, SE);
       ExactFPMathInst = ExactFPMathInst == nullptr
                             ? ReduxDesc.getExactFPMathInst()
                             : ExactFPMathInst;
-      if (!ReduxDesc.isRecurrence())
+      if (!ReduxDesc.isRecurrence()) {
+        if (!ReduxDesc.isCandidateUser())
           return false;
+
+        // TODO: Only allow one user recurrence now.
+        if (UserRecurPHI)
+          return false;
+
+        UserRecurPHI = ReduxDesc.getCandUserRecurPhi();
+        UserRecurKind = ReduxDesc.getCandUserRecurKind();
+  // TODO: Call AddReductionVar here?
+
+        // Fix NumCmpSelectPatternInst
+        if (auto *SI = dyn_cast<SelectInst>(Cur)) {
+          auto *CI = dyn_cast<CmpInst>(SI->getCondition());
+          if (CI->hasOneUse())
+            --NumCmpSelectPatternInst;
+        }
+        // Stop visiting the users of current instruction if it contains user
+        // recurrence.
+        continue;
+      }
       // FIXME: FMF is allowed on phi, but propagation is not handled correctly.
       if (isa<FPMathOperator>(ReduxDesc.getPatternInst()) && !IsAPhi) {
         FastMathFlags CurFMF = ReduxDesc.getPatternInst()->getFastMathFlags();
         if (auto *Sel = dyn_cast<SelectInst>(ReduxDesc.getPatternInst())) {
           // Accept FMF on either fcmp or select of a min/max idiom.
           // TODO: This is a hack to work-around the fact that FMF may not be
           //       assigned/propagated correctly. If that problem is fixed or we
           //       standardize on fmin/fmax via intrinsics, this can be removed.
           if (auto *FCmp = dyn_cast<FCmpInst>(Sel->getCondition()))
if (!IsAPhi && !IsASelect && !isMinMaxRecurrenceKind(Kind) &&
         !isSelectCmpRecurrenceKind(Kind) &&
         hasMultipleUsesOf(Cur, VisitedInsts, 1))
       return false;
 
     // All inputs to a PHI node must be a reduction value.
     if (IsAPhi && Cur != Phi && !areAllUsesIn(Cur, VisitedInsts))
       return false;
 
-    if ((isIntMinMaxRecurrenceKind(Kind) || Kind == RecurKind::SelectICmp) &&
+    if ((isIntMinMaxRecurrenceKind(Kind) || Kind == RecurKind::SelectICmp ||
+         Kind == RecurKind::SelectIVICmp) &&
         (isa<ICmpInst>(Cur) || isa<SelectInst>(Cur)))
       ++NumCmpSelectPatternInst;
-    if ((isFPMinMaxRecurrenceKind(Kind) || Kind == RecurKind::SelectFCmp) &&
+    if ((isFPMinMaxRecurrenceKind(Kind) || Kind == RecurKind::SelectFCmp ||
+         Kind == RecurKind::SelectIVFCmp) &&
         (isa<FCmpInst>(Cur) || isa<SelectInst>(Cur)))
       ++NumCmpSelectPatternInst;
 
     // Check  whether we found a reduction operator.
     FoundReduxOp |= !IsAPhi && Cur != Start;
 
     // Process users of current instruction. Push non-PHI nodes after PHI nodes
     // onto the stack. This way we are going to have seen all inputs to PHI
for (User *U : Cur->users()) {
             return false;
           }
           NonPHIs.push_back(UI);
         }
       } else if (!isa<PHINode>(UI) &&
                  ((!isa<FCmpInst>(UI) && !isa<ICmpInst>(UI) &&
                    !isa<SelectInst>(UI)) ||
                   (!isConditionalRdxPattern(Kind, UI).isRecurrence() &&
-                   !isSelectCmpPattern(TheLoop, Phi, UI, IgnoredVal)
+                   !isSelectCmpPattern(TheLoop, Phi, UI, IgnoredVal, SE)
                         .isRecurrence() &&
-                   !isMinMaxPattern(UI, Kind, IgnoredVal).isRecurrence())))
+                   !isMinMaxPattern(UI, Kind, IgnoredVal, TheLoop, Phi, SE)
+                        .isRecurrence())))
         return false;
 
       // Remember that we completed the cycle.
       if (UI == Phi)
         FoundStartPHI = true;
     }
     Worklist.append(PHIs.begin(), PHIs.end());
     Worklist.append(NonPHIs.begin(), NonPHIs.end());
bool RecurrenceDescriptor::AddReductionVar(
   // only have a single instruction with out-of-loop users.
 
   // The ExitInstruction(Instruction which is allowed to have out-of-loop users)
   // is saved as part of the RecurrenceDescriptor.
 
   // Save the description of this reduction variable.
   RecurrenceDescriptor RD(RdxStart, ExitInstruction, IntermediateStore, Kind,
                           FMF, ExactFPMathInst, RecurrenceType, IsSigned,
-                          IsOrdered, CastInsts, MinWidthCastToRecurrenceType);
+                          IsOrdered, CastInsts, MinWidthCastToRecurrenceType,
+                          UserRecurPHI, UserRecurKind);
   RedDes = RD;
 
   return true;
 }
 
 // We are looking for loops that do something like this:
 //   int r = 0;
 //   for (int i = 0; i < n; i++) {

 // any two non-constants, provided they are loop invariant. The only thing
 // we actually care about at the end of the loop is whether or not any lane
 // in the selected vector is different from the start value. The final
 // across-vector reduction after the loop simply involves choosing the start
 // value if nothing changed (0 in the example above) or the other selected
 // value (3 in the example above).
 RecurrenceDescriptor::InstDesc
 RecurrenceDescriptor::isSelectCmpPattern(Loop *Loop, PHINode *OrigPhi,
-                                         Instruction *I, InstDesc &Prev) {
+                                         Instruction *I, InstDesc &Prev,
+                                         ScalarEvolution *SE) {
   // We must handle the select(cmp(),x,y) as a single instruction. Advance to
   // the select.
   CmpInst::Predicate Pred;
   if (match(I, m_OneUse(m_Cmp(Pred, m_Value(), m_Value())))) {
     if (auto *Select = dyn_cast<SelectInst>(*I->user_begin()))
       return InstDesc(Select, Prev.getRecKind());
   }
 
   // Only match select with single use cmp condition.
   if (!match(I, m_Select(m_OneUse(m_Cmp(Pred, m_Value(), m_Value())), m_Value(),
                          m_Value())))
     return InstDesc(false, I);
 
   SelectInst *SI = cast<SelectInst>(I);
   Value *NonPhi = nullptr;
 
   if (OrigPhi == dyn_cast<PHINode>(SI->getTrueValue()))
     NonPhi = SI->getFalseValue();
   else if (OrigPhi == dyn_cast<PHINode>(SI->getFalseValue()))
     NonPhi = SI->getTrueValue();
   else
     return InstDesc(false, I);
 
+  auto isIncreasingLoopInduction = [&SE, &Loop](Value *V) {
+    if (!SE)
+      return false;
+
+    auto *Phi = dyn_cast<PHINode>(V);
+    if (!Phi)
+      return false;
+
+    auto LB = Loop::LoopBounds::getBounds(*Loop, *Phi, *SE);
+    if (!LB)
+      return false;
+
+    auto Direction = LB->getDirection();
+    return Direction == Loop::LoopBounds::Direction::Increasing;
+  };
+
   // We are looking for selects of the form:
   //   select(cmp(), phi, loop_invariant) or
   //   select(cmp(), loop_invariant, phi)
-  if (!Loop->isLoopInvariant(NonPhi))
-    return InstDesc(false, I);
-
+  if (Loop->isLoopInvariant(NonPhi))
     return InstDesc(I, isa<ICmpInst>(I->getOperand(0)) ? RecurKind::SelectICmp
                                                        : RecurKind::SelectFCmp);
+  // or
+  //   select(cmp(), phi, loop_induction) or
+  //   select(cmp(), loop_induction, phi)
+  if (isIncreasingLoopInduction(NonPhi))
+    return InstDesc(I, isa<ICmpInst>(I->getOperand(0))
+                           ? RecurKind::SelectIVICmp
+                           : RecurKind::SelectIVFCmp);
+
+  return InstDesc(false, I);
 }
 
 RecurrenceDescriptor::InstDesc
 RecurrenceDescriptor::isMinMaxPattern(Instruction *I, RecurKind Kind,
-                                      const InstDesc &Prev) {
+                                      const InstDesc &Prev, Loop *Loop,
+                                      PHINode *OrigPhi, ScalarEvolution *SE) {
   assert((isa<CmpInst>(I) || isa<SelectInst>(I) || isa<CallInst>(I)) &&
          "Expected a cmp or select or call instruction");
   if (!isMinMaxRecurrenceKind(Kind))
     return InstDesc(false, I);
 
   // We must handle the select(cmp()) as a single instruction. Advance to the
   // select.
   CmpInst::Predicate Pred;
   if (match(I, m_OneUse(m_Cmp(Pred, m_Value(), m_Value())))) {
     if (auto *Select = dyn_cast<SelectInst>(*I->user_begin()))
       return InstDesc(Select, Prev.getRecKind());
   }
 
   // Only match select with single use cmp condition, or a min/max intrinsic.
   if (!isa<IntrinsicInst>(I) &&
       !match(I, m_Select(m_OneUse(m_Cmp(Pred, m_Value(), m_Value())), m_Value(),
                          m_Value())))
     return InstDesc(false, I);
 
+  RecurKind MMRK = isMinMaxOperation(I);
+  if (MMRK != RecurKind::None)
+    return InstDesc(Kind == MMRK, I);
+
+  if (isa<SelectInst>(I))
+    return isMinMaxIdxPattern(Loop, I, OrigPhi, Kind, SE);
+
+  return InstDesc(false, I);
+}
+
+RecurKind RecurrenceDescriptor::isMinMaxOperation(Instruction *I) {
   // Look for a min/max pattern.
   if (match(I, m_UMin(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::UMin, I);
+    return RecurKind::UMin;
   if (match(I, m_UMax(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::UMax, I);
+    return RecurKind::UMax;
   if (match(I, m_SMax(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::SMax, I);
+    return RecurKind::SMax;
   if (match(I, m_SMin(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::SMin, I);
+    return RecurKind::SMin;
   if (match(I, m_OrdFMin(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::FMin, I);
+    return RecurKind::FMin;
   if (match(I, m_OrdFMax(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::FMax, I);
+    return RecurKind::FMax;
   if (match(I, m_UnordFMin(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::FMin, I);
+    return RecurKind::FMin;
   if (match(I, m_UnordFMax(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::FMax, I);
+    return RecurKind::FMax;
   if (match(I, m_Intrinsic<Intrinsic::minnum>(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::FMin, I);
+    return RecurKind::FMin;
   if (match(I, m_Intrinsic<Intrinsic::maxnum>(m_Value(), m_Value())))
-    return InstDesc(Kind == RecurKind::FMax, I);
+    return RecurKind::FMax;
+
+  return RecurKind::None;
+}
 
+RecurrenceDescriptor::InstDesc RecurrenceDescriptor::isMinMaxIdxPattern(
+    Loop *Loop, Instruction *I, PHINode *MinMaxPhi, RecurKind MinMaxKind,
+    ScalarEvolution *SE) {
+  assert(isa<SelectInst>(I) && "Expected a select instruction");
+  // TODO: FP MinMax
+  if (!isIntMinMaxRecurrenceKind(MinMaxKind))
+    return InstDesc(false, I);
+
+  // Requires SCEV to check the index part
+  if (!SE) {
+    LLVM_DEBUG(dbgs() << "MinMaxIdx patterns are not recognized without "
+                      << "Scalar Evolution Analysis\n");
     return InstDesc(false, I);
   }
 
+  // Check the index select
+  auto *SI = dyn_cast<SelectInst>(I);
+  auto *CI = dyn_cast<CmpInst>(SI->getCondition());
+  Value *LHS = CI->getOperand(0), *RHS = CI->getOperand(1);
+
+  // %cmp = icmp pred, %mmphi, %0
+  // %select = select %cmp, %update, %idxphi
+  // Check if cmp used min/max phi
+  bool IsLHSPhi;
+  if (MinMaxPhi == dyn_cast<PHINode>(LHS))
+    IsLHSPhi = true;
+  else if (MinMaxPhi == dyn_cast<PHINode>(RHS))
+    IsLHSPhi = false;
+  else
+    return InstDesc(false, I);
+
+  // Normalize the predicate, and get which side the select should update idx
+  // TODO: Need to consider commutable.
+  CmpInst::Predicate NormPred =
+      IsLHSPhi ? CI->getPredicate() : CI->getInversePredicate();
+  bool UpdateSide;
+  RecurKind ExpectedIdxRK;
+  switch (NormPred) {
+  case CmpInst::ICMP_SLT:
+  case CmpInst::ICMP_ULT:
+    // %mmphi <  %0
+    UpdateSide = isMaxRecurrenceKind(MinMaxKind);
+    ExpectedIdxRK = isMaxRecurrenceKind(MinMaxKind) ? RecurKind::MinMaxFirstIdx
+                                                    : RecurKind::MinMaxLastIdx;
+    break;
+  case CmpInst::ICMP_SLE:
+  case CmpInst::ICMP_ULE:
+    // %mmphi <= %0
+    UpdateSide = isMaxRecurrenceKind(MinMaxKind);
+    ExpectedIdxRK = isMaxRecurrenceKind(MinMaxKind) ? RecurKind::MinMaxLastIdx
+                                                    : RecurKind::MinMaxFirstIdx;
+    break;
+  case CmpInst::ICMP_SGT:
+  case CmpInst::ICMP_UGT:
+    // %mmphi >  %0
+    UpdateSide = !isMaxRecurrenceKind(MinMaxKind);
+    ExpectedIdxRK = isMaxRecurrenceKind(MinMaxKind) ? RecurKind::MinMaxLastIdx
+                                                    : RecurKind::MinMaxFirstIdx;
+    break;
+  case CmpInst::ICMP_SGE:
+  case CmpInst::ICMP_UGE:
+    // %mmphi >= %0
+    UpdateSide = !isMaxRecurrenceKind(MinMaxKind);
+    ExpectedIdxRK = isMaxRecurrenceKind(MinMaxKind) ? RecurKind::MinMaxFirstIdx
+                                                    : RecurKind::MinMaxLastIdx;
+    break;
+  default:
+    return InstDesc(false, I);
+  }
+
+  // Get the reduction phi of index select
+  Value *IdxUpdateV = UpdateSide ? SI->getTrueValue() : SI->getFalseValue();
+  Value *IdxReduxV = UpdateSide ? SI->getFalseValue() : SI->getTrueValue();
+  // Handle the operand of index select may have been casted.
+  if (auto *Cast = dyn_cast<CastInst>(IdxUpdateV))
+    IdxUpdateV = Cast->getOperand(0);
+
+  auto *IdxUpdatePhi = dyn_cast<PHINode>(IdxUpdateV);
+  auto *IdxReduxPhi = dyn_cast<PHINode>(IdxReduxV);
+  if (!IdxUpdatePhi || !IdxReduxPhi)
+    return InstDesc(false, I);
+
+  // Check update side is a loop induction variable
+  InductionDescriptor ID;
+  if (!InductionDescriptor::isInductionPHI(IdxUpdatePhi, Loop, SE, ID))
+    return InstDesc(false, I);
+
+  // The reduction phi of index select and reduction phi of min/max must not the
+  // same
+  if (IdxReduxPhi == MinMaxPhi)
+    return InstDesc(false, I);
+
+  return InstDesc(false, I, IdxReduxPhi, ExpectedIdxRK);
+}
+
 /// Returns true if the select instruction has users in the compare-and-add
 /// reduction pattern below. The select instruction argument is the last one
 /// in the sequence.
 ///
 /// %sum.1 = phi ...
 /// ...
 /// %cmp = fcmp pred %0, %CFP
 /// %add = fadd %0, %sum.1
RecurrenceDescriptor::isConditionalRdxPattern(RecurKind Kind, Instruction *I) {
   Instruction *IPhi = isa<PHINode>(*Op1) ? dyn_cast<Instruction>(Op1)
                                          : dyn_cast<Instruction>(Op2);
   if (!IPhi || IPhi != FalseVal)
     return InstDesc(false, I);
 
   return InstDesc(true, SI);
 }
 
-RecurrenceDescriptor::InstDesc
-RecurrenceDescriptor::isRecurrenceInstr(Loop *L, PHINode *OrigPhi,
-                                        Instruction *I, RecurKind Kind,
-                                        InstDesc &Prev, FastMathFlags FuncFMF) {
+RecurrenceDescriptor::InstDesc RecurrenceDescriptor::isRecurrenceInstr(
+    Loop *L, PHINode *OrigPhi, Instruction *I, RecurKind Kind, InstDesc &Prev,
+    FastMathFlags FuncFMF, ScalarEvolution *SE) {
   assert(Prev.getRecKind() == RecurKind::None || Prev.getRecKind() == Kind);
   switch (I->getOpcode()) {
   default:
     return InstDesc(false, I);
   case Instruction::PHI:
     return InstDesc(I, Prev.getRecKind(), Prev.getExactFPMathInst());
   case Instruction::Sub:
   case Instruction::Add:
case Instruction::Select:
     if (Kind == RecurKind::FAdd || Kind == RecurKind::FMul ||
         Kind == RecurKind::Add || Kind == RecurKind::Mul)
       return isConditionalRdxPattern(Kind, I);
     [[fallthrough]];
   case Instruction::FCmp:
   case Instruction::ICmp:
   case Instruction::Call:
     if (isSelectCmpRecurrenceKind(Kind))
-      return isSelectCmpPattern(L, OrigPhi, I, Prev);
+      return isSelectCmpPattern(L, OrigPhi, I, Prev, SE);
     if (isIntMinMaxRecurrenceKind(Kind) ||
         (((FuncFMF.noNaNs() && FuncFMF.noSignedZeros()) ||
           (isa<FPMathOperator>(I) && I->hasNoNaNs() &&
            I->hasNoSignedZeros())) &&
          isFPMinMaxRecurrenceKind(Kind)))
-      return isMinMaxPattern(I, Kind, Prev);
+      return isMinMaxPattern(I, Kind, Prev, L, OrigPhi, SE);
     else if (isFMulAddIntrinsic(I))
       return InstDesc(Kind == RecurKind::FMulAdd, I,
                       I->hasAllowReassoc() ? nullptr : I);
     return InstDesc(false, I);
   }
 }
 
 bool RecurrenceDescriptor::hasMultipleUsesOf(
case RecurKind::FMin:
     return ConstantFP::getInfinity(Tp, false /*Negative*/);
   case RecurKind::FMax:
     assert((FMF.noNaNs() && FMF.noSignedZeros()) &&
            "nnan, nsz is expected to be set for FP max reduction.");
     return ConstantFP::getInfinity(Tp, true /*Negative*/);
   case RecurKind::SelectICmp:
   case RecurKind::SelectFCmp:
     return getRecurrenceStartValue();
     break;
+  case RecurKind::SelectIVICmp:
+  case RecurKind::SelectIVFCmp:
+  case RecurKind::MinMaxFirstIdx:
+  case RecurKind::MinMaxLastIdx:
+    // FIXME: SMax or UMax, I'm not sure which one is correct.
+    return getRecurrenceIdentity(RecurKind::SMax, Tp, FMF);
   default:
     llvm_unreachable("Unknown recurrence kind");
   }
 }
 
 unsigned RecurrenceDescriptor::getOpcode(RecurKind Kind) {
   switch (Kind) {
   case RecurKind::Add:
     return Instruction::Add;
unsigned RecurrenceDescriptor::getOpcode(RecurKind Kind) {
   case RecurKind::FMulAdd:
   case RecurKind::FAdd:
     return Instruction::FAdd;
   case RecurKind::SMax:
   case RecurKind::SMin:
   case RecurKind::UMax:
   case RecurKind::UMin:
   case RecurKind::SelectICmp:
+  case RecurKind::SelectIVICmp:
+  // TODO: maybe new FMinMaxFirstIdx/ FMinMaxLastIdx
+  case RecurKind::MinMaxFirstIdx:
+  case RecurKind::MinMaxLastIdx:
     return Instruction::ICmp;
   case RecurKind::FMax:
   case RecurKind::FMin:
   case RecurKind::SelectFCmp:
+  case RecurKind::SelectIVFCmp:
     return Instruction::FCmp;
   default:
     llvm_unreachable("Unknown recurrence operation");
   }
 }
 
 SmallVector<Instruction *, 4>
 RecurrenceDescriptor::getReductionOpChain(PHINode *Phi, Loop *L) const {

llvm/lib/Transforms/Utils/LoopUtils.cpp

if (Op != Instruction::ICmp && Op != Instruction::FCmp) {
              "Invalid min/max");
       TmpVec = createMinMaxOp(Builder, RdxKind, TmpVec, Shuf);
     }
   }
   // The result is in the first element of the vector.
   return Builder.CreateExtractElement(TmpVec, Builder.getInt32(0));
 }
 
-Value *llvm::createSelectCmpTargetReduction(IRBuilderBase &Builder,
-                                            const TargetTransformInfo *TTI,
-                                            Value *Src,
-                                            const RecurrenceDescriptor &Desc,
-                                            PHINode *OrigPhi) {
-  assert(RecurrenceDescriptor::isSelectCmpRecurrenceKind(
-             Desc.getRecurrenceKind()) &&
+Value *llvm::createInvariantSelectCmpTargetReduction(
+    IRBuilderBase &Builder, const TargetTransformInfo *TTI, Value *Src,
+    const RecurrenceDescriptor &Desc, PHINode *OrigPhi) {
+  assert((Desc.getRecurrenceKind() == RecurKind::SelectICmp ||
+          Desc.getRecurrenceKind() == RecurKind::SelectFCmp) &&
          "Unexpected reduction kind");
   Value *InitVal = Desc.getRecurrenceStartValue();
   Value *NewVal = nullptr;
 
   // First use the original phi to determine the new value we're trying to
   // select from in the loop.
   SelectInst *SI = nullptr;
   for (auto *U : OrigPhi->users()) {
Value *llvm::createInvariantSelectCmpTargetReduction(
   Value *Cmp =
       Builder.CreateCmp(CmpInst::ICMP_NE, Src, Right, "rdx.select.cmp");
 
   // If any predicate is true it means that we want to select the new value.
   Cmp = Builder.CreateOrReduce(Cmp);
   return Builder.CreateSelect(Cmp, NewVal, InitVal, "rdx.select");
 }
 
+Value *llvm::createInductionSelectCmpTargetReduction(
+    IRBuilderBase &Builder, const TargetTransformInfo *TTI, Value *Src,
+    const RecurrenceDescriptor &Desc, PHINode *OrigPhi) {
+  assert((Desc.getRecurrenceKind() == RecurKind::SelectIVICmp ||
+          Desc.getRecurrenceKind() == RecurKind::SelectIVFCmp) &&
+         "Unexpected reduction kind");
+  Value *InitVal = Desc.getRecurrenceStartValue();
+  Value *NewVal = nullptr;
+  Value *Cmp = nullptr;
+  auto *SrcVecEltTy = cast<VectorType>(Src->getType())->getElementType();
+  Value *Iden = Desc.getRecurrenceIdentity(
+      Desc.getRecurrenceKind(), SrcVecEltTy, Desc.getFastMathFlags());
+
+  // FIXME: SMax or UMax?
+  // TODO: Decreasing induction need fix here
+  NewVal = Builder.CreateIntMaxReduce(Src, true);
+  Cmp = Builder.CreateCmp(CmpInst::ICMP_NE, NewVal, Iden, "rdx.select.cmp");
+
+  return Builder.CreateSelect(Cmp, NewVal, InitVal, "rdx.select");
+}
+
+Value *llvm::createMMISelectCmpTargetReduction(
+    IRBuilderBase &Builder, const TargetTransformInfo *TTI, Value *Src,
+    const RecurrenceDescriptor &Desc, PHINode *OrigPhi, Value *SrcMask) {
+  assert(RecurrenceDescriptor::isMinMaxIdxRecurrenceKind(
+             Desc.getRecurrenceKind()) &&
+         "Unexpected reduction kind");
+  RecurKind Kind = Desc.getRecurrenceKind();
+  Value *InitVal = Desc.getRecurrenceStartValue();
+  Value *NewVal = Src;
+  Value *Cmp = nullptr;
+  auto *SrcVecEltTy = cast<VectorType>(Src->getType())->getElementType();
+  Value *Iden =
+      Desc.getRecurrenceIdentity(Kind, SrcVecEltTy, Desc.getFastMathFlags());
+
+  // FIXME: UMax/SMax or UMin/UMax?
+  RecurKind RdxExtractK =
+      Kind == RecurKind::MinMaxFirstIdx ? RecurKind::SMin : RecurKind::SMax;
+  // TODO: If vp reduction intrinsic is supported, there is no need to generate
+  // additional select here.
+  if (SrcMask) {
+    Value *RdxOpIden = Desc.getRecurrenceIdentity(RdxExtractK, SrcVecEltTy,
+                                                  Desc.getFastMathFlags());
+    ElementCount EC = cast<VectorType>(NewVal->getType())->getElementCount();
+    RdxOpIden = Builder.CreateVectorSplat(EC, RdxOpIden);
+    NewVal = Builder.CreateSelect(SrcMask, NewVal, RdxOpIden, "mask.select");
+  }
+
+  NewVal = createSimpleTargetReduction(Builder, TTI, NewVal, RdxExtractK);
+  Cmp = Builder.CreateCmp(CmpInst::ICMP_NE, NewVal, Iden, "rdx.select.cmp");
+
+  return Builder.CreateSelect(Cmp, NewVal, InitVal, "rdx.select");
+}
+
+Value *llvm::createSelectCmpTargetReduction(IRBuilderBase &Builder,
+                                            const TargetTransformInfo *TTI,
+                                            Value *Src,
+                                            const RecurrenceDescriptor &Desc,
+                                            PHINode *OrigPhi, Value *SrcMask) {
+  assert(RecurrenceDescriptor::isSelectCmpRecurrenceKind(
+             Desc.getRecurrenceKind()) &&
+         "Unexpected reduction kind");
+  RecurKind RdxKind = Desc.getRecurrenceKind();
+  switch (RdxKind) {
+  case RecurKind::SelectICmp:
+  case RecurKind::SelectFCmp:
+    return createInvariantSelectCmpTargetReduction(Builder, TTI, Src, Desc,
+                                                   OrigPhi);
+  case RecurKind::SelectIVICmp:
+  case RecurKind::SelectIVFCmp:
+    return createInductionSelectCmpTargetReduction(Builder, TTI, Src, Desc,
+                                                   OrigPhi);
+  case RecurKind::MinMaxFirstIdx:
+  case RecurKind::MinMaxLastIdx:
+    return createMMISelectCmpTargetReduction(Builder, TTI, Src, Desc, OrigPhi,
+                                             SrcMask);
+  default:
+    llvm_unreachable("Unknown SelectCmp recurrence kind");
+  }
+}
+
 Value *llvm::createSimpleTargetReduction(IRBuilderBase &Builder,
                                          const TargetTransformInfo *TTI,
                                          Value *Src, RecurKind RdxKind) {
   auto *SrcVecEltTy = cast<VectorType>(Src->getType())->getElementType();
   switch (RdxKind) {
   case RecurKind::Add:
     return Builder.CreateAddReduce(Src);
   case RecurKind::Mul:
Value *llvm::createSimpleTargetReduction(IRBuilderBase &Builder,
   default:
     llvm_unreachable("Unhandled opcode");
   }
 }
 
 Value *llvm::createTargetReduction(IRBuilderBase &B,
                                    const TargetTransformInfo *TTI,
                                    const RecurrenceDescriptor &Desc, Value *Src,
-                                   PHINode *OrigPhi) {
+                                   PHINode *OrigPhi, Value *SrcMask) {
   // TODO: Support in-order reductions based on the recurrence descriptor.
   // All ops in the reduction inherit fast-math-flags from the recurrence
   // descriptor.
   IRBuilderBase::FastMathFlagGuard FMFGuard(B);
   B.setFastMathFlags(Desc.getFastMathFlags());
 
   RecurKind RK = Desc.getRecurrenceKind();
   if (RecurrenceDescriptor::isSelectCmpRecurrenceKind(RK))
-    return createSelectCmpTargetReduction(B, TTI, Src, Desc, OrigPhi);
+    return createSelectCmpTargetReduction(B, TTI, Src, Desc, OrigPhi, SrcMask);
 
   return createSimpleTargetReduction(B, TTI, Src, RK);
 }
 
 Value *llvm::createOrderedReduction(IRBuilderBase &B,
                                     const RecurrenceDescriptor &Desc,
                                     Value *Src, Value *Start) {
   assert((Desc.getRecurrenceKind() == RecurKind::FAdd ||

llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp

for (Instruction &I : *BB) {
         reportVectorizationFailure("Value cannot be used outside the loop",
                                    "value cannot be used outside the loop",
                                    "ValueUsedOutsideLoop", ORE, TheLoop, &I);
         return false;
       }
     } // next instr.
   }
 
+  // Second comfirm the incomplete reductions
+  for (auto R : Reductions) {
+    RecurrenceDescriptor &RedDes = Reductions.find(R.first)->second;
+    if (!RedDes.hasUserRecurrence())
+      continue;
+
+    PHINode *UserPhi = RedDes.getUserRecurPhi();
+    if (!isReductionVariable(UserPhi))
+      return false;
+
+    RecurrenceDescriptor &UserRedDes = Reductions.find(UserPhi)->second;
+    if (!RedDes.fixUserRecurrence(UserRedDes))
+      return false;
+  }
+
   if (!PrimaryInduction) {
     if (Inductions.empty()) {
       reportVectorizationFailure("Did not find one integer induction var",
           "loop induction variable could not be identified",
           "NoInductionVariable", ORE, TheLoop);
       return false;
     } else if (!WidestIndTy) {
       reportVectorizationFailure("Did not find one integer induction var",

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

public:
   /// this is needed because each iteration in the loop corresponds to a SIMD
   /// element.
   virtual Value *getBroadcastInstrs(Value *V);
 
   // Returns the resume value (bc.merge.rdx) for a reduction as
   // generated by fixReduction.
   PHINode *getReductionResumeValue(const RecurrenceDescriptor &RdxDesc);
 
+  // Returns the recurrence mask (mask.cmp) for a recurrence as generated by
+  // fixReduction.
+  Value *getDependRecurrenceMask(const RecurrenceDescriptor &RdxDesc);
+
   /// Create a new phi node for the induction variable \p OrigPhi to resume
   /// iteration count in the scalar epilogue, from where the vectorized loop
   /// left off. In cases where the loop skeleton is more complicated (eg.
   /// epilogue vectorization) and the resume values can come from an additional
   /// bypass block, the \p AdditionalBypass pair provides information about the
   /// bypass block and the end value on the edge from bypass to this loop.
   PHINode *createInductionResumeValue(
       PHINode *OrigPhi, const InductionDescriptor &ID,
protected:
   /// Structure to hold information about generated runtime checks, responsible
   /// for cleaning the checks, if vectorization turns out unprofitable.
   GeneratedRTChecks &RTChecks;
 
   // Holds the resume values for reductions in the loops, used to set the
   // correct start value of reduction PHIs when vectorizing the epilogue.
   SmallMapVector<const RecurrenceDescriptor *, PHINode *, 4>
       ReductionResumeValues;
+
+  // Holds the masks for recurrences in the loops, be used for reduction when
+  // there is a reduction that depends on the recurrence.
+  SmallMapVector<const RecurrenceDescriptor *, Value *, 4>
+      DependRecurrenceMasks;
 };
 
 class InnerLoopUnroller : public InnerLoopVectorizer {
 public:
   InnerLoopUnroller(Loop *OrigLoop, PredicatedScalarEvolution &PSE,
                     LoopInfo *LI, DominatorTree *DT,
                     const TargetLibraryInfo *TLI,
                     const TargetTransformInfo *TTI, AssumptionCache *AC,
                     OptimizationRemarkEmitter *ORE, unsigned UnrollFactor,

 PHINode *InnerLoopVectorizer::getReductionResumeValue(
     const RecurrenceDescriptor &RdxDesc) {
   auto It = ReductionResumeValues.find(&RdxDesc);
   assert(It != ReductionResumeValues.end() &&
          "Expected to find a resume value for the reduction.");
   return It->second;
 }
 
+Value *InnerLoopVectorizer::getDependRecurrenceMask(
+    const RecurrenceDescriptor &RdxDesc) {
+  auto It = DependRecurrenceMasks.find(&RdxDesc);
+  assert(It != DependRecurrenceMasks.end() &&
+         "Expected to find a dependence mask for the recurrence.");
+  return It->second;
+}
+
 namespace llvm {
 
 // Loop vectorization cost-model hints how the scalar epilogue loop should be
 // lowered.
 enum ScalarEpilogueLowering {
 
   // The default: allowing scalar epilogues.
   CM_ScalarEpilogueAllowed,
void InnerLoopVectorizer::fixCrossIterationPHIs(VPTransformState &State) {
   // In order to support recurrences we need to be able to vectorize Phi nodes.
   // Phi nodes have cycles, so we need to vectorize them in two stages. This is
   // stage #2: We now need to fix the recurrences by adding incoming edges to
   // the currently empty PHI nodes. At this point every instruction in the
   // original loop is widened to a vector form so we can use them to construct
   // the incoming edges.
   VPBasicBlock *Header =
       State.Plan->getVectorLoopRegion()->getEntryBasicBlock();
-  for (VPRecipeBase &R : Header->phis()) {
-    if (auto *ReductionPhi = dyn_cast<VPReductionPHIRecipe>(&R))
+  // FIXME: Maybe I should not choose std::queue...
+  std::queue<VPRecipeBase *> Worklist;
+  for (VPRecipeBase &R : Header->phis())
+    Worklist.push(&R);
+
+  while (!Worklist.empty()) {
+    VPRecipeBase &R = *(Worklist.front());
+    Worklist.pop();
+    if (auto *ReductionPhi = dyn_cast<VPReductionPHIRecipe>(&R)) {
+      const RecurrenceDescriptor &RecDesc =
+          ReductionPhi->getRecurrenceDescriptor();
+      RecurrenceDescriptor *DependRecDesc = RecDesc.getDependMinMaxRecDes();
+      if (DependRecDesc && !DependRecurrenceMasks.count(DependRecDesc)) {
+        Worklist.push(&R);
+        continue;
+      }
       fixReduction(ReductionPhi, State);
-    else if (auto *FOR = dyn_cast<VPFirstOrderRecurrencePHIRecipe>(&R))
+    } else if (auto *FOR = dyn_cast<VPFirstOrderRecurrencePHIRecipe>(&R))
       fixFixedOrderRecurrence(FOR, State);
   }
 }
 
 void InnerLoopVectorizer::fixFixedOrderRecurrence(
     VPFirstOrderRecurrencePHIRecipe *PhiR, VPTransformState &State) {
   // This is the second phase of vectorizing first-order recurrences. An
   // overview of the transformation is described below. Suppose we have the
for (unsigned Part = 1; Part < UF; ++Part) {
         ReducedPartRdx = Builder.CreateBinOp(
             (Instruction::BinaryOps)Op, RdxPart, ReducedPartRdx, "bin.rdx");
       } else if (RecurrenceDescriptor::isSelectCmpRecurrenceKind(RK))
         ReducedPartRdx = createSelectCmpOp(Builder, ReductionStartValue, RK,
                                            ReducedPartRdx, RdxPart);
       else
         ReducedPartRdx = createMinMaxOp(Builder, RK, ReducedPartRdx, RdxPart);
     }
   }
 
   // Create the reduction after the loop. Note that inloop reductions create the
   // target reduction in the loop using a Reduction recipe.
   if (VF.isVector() && !PhiR->isInLoop()) {
-    ReducedPartRdx =
-        createTargetReduction(Builder, TTI, RdxDesc, ReducedPartRdx, OrigPhi);
+    // Get the reduction mask if the reduction depend on another one.
+    Value *DependMask = nullptr;
+    RecurrenceDescriptor *DependDesc = RdxDesc.getDependMinMaxRecDes();
+    if (DependDesc) {
+      Builder.SetInsertPoint(&*LoopMiddleBlock->getTerminator());
+      DependMask = getDependRecurrenceMask(*DependDesc);
+    }
+
+    Value *ReducedPart = ReducedPartRdx;
+    ReducedPartRdx = createTargetReduction(Builder, TTI, RdxDesc,
+                                           ReducedPartRdx, OrigPhi, DependMask);
     // If the reduction can be performed in a smaller type, we need to extend
     // the reduction to the wider type before we branch to the original loop.
     if (PhiTy != RdxDesc.getRecurrenceType())
       ReducedPartRdx = RdxDesc.isSigned()
                            ? Builder.CreateSExt(ReducedPartRdx, PhiTy)
                            : Builder.CreateZExt(ReducedPartRdx, PhiTy);
+
+    // Create depend recurrence mask on demand.
+    if (RdxDesc.hasUserRecurrence()) {
+      ElementCount EC =
+          cast<VectorType>(ReducedPart->getType())->getElementCount();
+      Value *RdxSplat = Builder.CreateVectorSplat(EC, ReducedPartRdx);
+      // FIXME: Not sure use FCMP_OEQ is right or not.
+      CmpInst::Predicate MaskPred =
+          (ReducedPartRdx->getType()->isFloatingPointTy()) ? CmpInst::FCMP_OEQ
+                                                           : CmpInst::ICMP_EQ;
+      Value *Mask =
+          Builder.CreateCmp(MaskPred, RdxSplat, ReducedPart, "mask.cmp");
+      DependRecurrenceMasks.insert({&RdxDesc, Mask});
+    }
   }
 
   PHINode *ResumePhi =
       dyn_cast<PHINode>(PhiR->getStartValue()->getUnderlyingValue());
 
   // Create a phi node that merges control-flow from the backedge-taken check
   // block and the middle block.
   PHINode *BCBlockPhi = PHINode::Create(PhiTy, 2, "bc.merge.rdx",

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

void VPReductionPHIRecipe::execute(VPTransformState &State) {
   // Reductions do not have to start at zero. They can start with
   // any loop invariant values.
   VPValue *StartVPV = getStartValue();
   Value *StartV = StartVPV->getLiveInIRValue();
 
   Value *Iden = nullptr;
   RecurKind RK = RdxDesc.getRecurrenceKind();
   if (RecurrenceDescriptor::isMinMaxRecurrenceKind(RK) ||
-      RecurrenceDescriptor::isSelectCmpRecurrenceKind(RK)) {
+      (RK == RecurKind::SelectICmp || RK == RecurKind::SelectFCmp)) {
     // MinMax reduction have the start value as their identify.
     if (ScalarPHI) {
       Iden = StartV;
     } else {
       IRBuilderBase::InsertPointGuard IPBuilder(Builder);
       Builder.SetInsertPoint(VectorPH->getTerminator());
       StartV = Iden =
           Builder.CreateVectorSplat(State.VF, StartV, "minmax.ident");

llvm/test/Transforms/LoopVectorize/select-min-index.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -passes=loop-vectorize -force-vector-width=4 -S %s | FileCheck %s
 
 ; Test cases for selecting the index with the minimum value.
 
 define i64 @test_vectorize_select_umin_idx(ptr %src) {
 ; CHECK-LABEL: @test_vectorize_select_umin_idx(
 ; CHECK-NOT:   vector.body:
 ;
loop:
   %exitcond.not = icmp eq i64 %iv.next, 0
   br i1 %exitcond.not, label %exit, label %loop
 
 exit:
   %res = phi i64 [ %min.idx.next, %loop ]
   ret i64 %res
 }
 
+define i64 @test_vectorize_select_umin_idx_all_exit_inst(ptr %src, ptr %umin) {
+; CHECK-LABEL: @test_vectorize_select_umin_idx_all_exit_inst(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 true, label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i64> [ <i64 0, i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808>, [[VECTOR_PH]] ], [ [[TMP5:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x i64> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP4:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i64, ptr [[SRC:%.*]], i64 [[TMP0]]
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr i64, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i64>, ptr [[TMP2]], align 4
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ugt <4 x i64> [[VEC_PHI1]], [[WIDE_LOAD]]
+; CHECK-NEXT:    [[TMP4]] = call <4 x i64> @llvm.umin.v4i64(<4 x i64> [[VEC_PHI1]], <4 x i64> [[WIDE_LOAD]])
+; CHECK-NEXT:    [[TMP5]] = select <4 x i1> [[TMP3]], <4 x i64> [[VEC_IND]], <4 x i64> [[VEC_PHI]]
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i64> [[VEC_IND]], <i64 4, i64 4, i64 4, i64 4>
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i64 [[INDEX_NEXT]], 0
+; CHECK-NEXT:    br i1 [[TMP6]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[TMP7:%.*]] = call i64 @llvm.vector.reduce.umin.v4i64(<4 x i64> [[TMP4]])
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[TMP7]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <4 x i64> [[DOTSPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[MASK_CMP:%.*]] = icmp eq <4 x i64> [[DOTSPLAT]], [[TMP4]]
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 0, 0
+; CHECK-NEXT:    [[MASK_SELECT:%.*]] = select <4 x i1> [[MASK_CMP]], <4 x i64> [[TMP5]], <4 x i64> <i64 9223372036854775807, i64 9223372036854775807, i64 9223372036854775807, i64 9223372036854775807>
+; CHECK-NEXT:    [[TMP8:%.*]] = call i64 @llvm.vector.reduce.smin.v4i64(<4 x i64> [[MASK_SELECT]])
+; CHECK-NEXT:    [[RDX_SELECT_CMP:%.*]] = icmp ne i64 [[TMP8]], -9223372036854775808
+; CHECK-NEXT:    [[RDX_SELECT:%.*]] = select i1 [[RDX_SELECT_CMP]], i64 [[TMP8]], i64 0
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ 0, [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i64 [ 0, [[ENTRY]] ], [ [[TMP7]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX2:%.*]] = phi i64 [ 0, [[ENTRY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[MIN_IDX:%.*]] = phi i64 [ [[BC_MERGE_RDX2]], [[SCALAR_PH]] ], [ [[MIN_IDX_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[MIN_VAL:%.*]] = phi i64 [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[MIN_VAL_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i64, ptr [[SRC]], i64 [[IV]]
+; CHECK-NEXT:    [[L:%.*]] = load i64, ptr [[GEP]], align 4
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i64 [[MIN_VAL]], [[L]]
+; CHECK-NEXT:    [[MIN_VAL_NEXT]] = tail call i64 @llvm.umin.i64(i64 [[MIN_VAL]], i64 [[L]])
+; CHECK-NEXT:    [[MIN_IDX_NEXT]] = select i1 [[CMP]], i64 [[IV]], i64 [[MIN_IDX]]
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
+; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[IV_NEXT]], 0
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[EXIT]], label [[LOOP]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[RES:%.*]] = phi i64 [ [[MIN_IDX_NEXT]], [[LOOP]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[RES_UMIN:%.*]] = phi i64 [ [[MIN_VAL_NEXT]], [[LOOP]] ], [ [[TMP7]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    store i64 [[RES_UMIN]], ptr [[UMIN:%.*]], align 4
+; CHECK-NEXT:    ret i64 [[RES]]
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %min.idx = phi i64 [ 0, %entry ], [ %min.idx.next, %loop ]
+  %min.val = phi i64 [ 0, %entry ], [ %min.val.next, %loop ]
+  %gep = getelementptr i64, ptr %src, i64 %iv
+  %l = load i64, ptr %gep
+  %cmp = icmp ugt i64 %min.val, %l
+  %min.val.next = tail call i64 @llvm.umin.i64(i64 %min.val, i64 %l)
+  %min.idx.next = select i1 %cmp, i64 %iv, i64 %min.idx
+  %iv.next = add nuw nsw i64 %iv, 1
+  %exitcond.not = icmp eq i64 %iv.next, 0
+  br i1 %exitcond.not, label %exit, label %loop
+
+exit:
+  %res = phi i64 [ %min.idx.next, %loop ]
+  %res.umin = phi i64 [ %min.val.next, %loop ]
+  store i64 %res.umin, ptr %umin
+  ret i64 %res
+}
+
 define i64 @test_vectorize_select_umin_idx_min_ops_switched(ptr %src) {
 ; CHECK-LABEL: @test_vectorize_select_umin_idx_min_ops_switched(
 ; CHECK-NOT:   vector.body:
 ;
 entry:
   br label %loop
 
 loop:
loop:
   %exitcond.not = icmp eq i64 %iv.next, 0
   br i1 %exitcond.not, label %exit, label %loop
 
 exit:
   %res = phi i64 [ %min.idx.next, %loop ]
   ret i64 %res
 }
 
 define i64 @test_not_vectorize_select_no_min_reduction(ptr %src) {
 ; CHECK-LABEL: @test_not_vectorize_select_no_min_reduction(
-; CHECK-NOT:   vector.body:
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 true, label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i64> [ <i64 0, i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808>, [[VECTOR_PH]] ], [ [[TMP7:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VECTOR_RECUR:%.*]] = phi <4 x i64> [ <i64 poison, i64 poison, i64 poison, i64 0>, [[VECTOR_PH]] ], [ [[TMP3:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i64, ptr [[SRC:%.*]], i64 [[TMP0]]
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr i64, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i64>, ptr [[TMP2]], align 4
+; CHECK-NEXT:    [[TMP3]] = add <4 x i64> [[WIDE_LOAD]], <i64 1, i64 1, i64 1, i64 1>
+; CHECK-NEXT:    [[TMP4:%.*]] = shufflevector <4 x i64> [[VECTOR_RECUR]], <4 x i64> [[TMP3]], <4 x i32> <i32 3, i32 4, i32 5, i32 6>
+; CHECK-NEXT:    [[TMP5:%.*]] = icmp ugt <4 x i64> [[TMP4]], [[WIDE_LOAD]]
+; CHECK-NEXT:    [[TMP6:%.*]] = call <4 x i64> @llvm.umin.v4i64(<4 x i64> [[TMP4]], <4 x i64> [[WIDE_LOAD]])
+; CHECK-NEXT:    [[TMP7]] = select <4 x i1> [[TMP5]], <4 x i64> [[VEC_IND]], <4 x i64> [[VEC_PHI]]
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i64> [[VEC_IND]], <i64 4, i64 4, i64 4, i64 4>
+; CHECK-NEXT:    [[TMP8:%.*]] = icmp eq i64 [[INDEX_NEXT]], 0
+; CHECK-NEXT:    br i1 [[TMP8]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[TMP9:%.*]] = call i64 @llvm.vector.reduce.smax.v4i64(<4 x i64> [[TMP7]])
+; CHECK-NEXT:    [[RDX_SELECT_CMP:%.*]] = icmp ne i64 [[TMP9]], -9223372036854775808
+; CHECK-NEXT:    [[RDX_SELECT:%.*]] = select i1 [[RDX_SELECT_CMP]], i64 [[TMP9]], i64 0
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 0, 0
+; CHECK-NEXT:    [[VECTOR_RECUR_EXTRACT:%.*]] = extractelement <4 x i64> [[TMP3]], i32 3
+; CHECK-NEXT:    [[VECTOR_RECUR_EXTRACT_FOR_PHI:%.*]] = extractelement <4 x i64> [[TMP3]], i32 2
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[SCALAR_RECUR_INIT:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[VECTOR_RECUR_EXTRACT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ 0, [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i64 [ 0, [[ENTRY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[MIN_IDX:%.*]] = phi i64 [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[MIN_IDX_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[SCALAR_RECUR:%.*]] = phi i64 [ [[SCALAR_RECUR_INIT]], [[SCALAR_PH]] ], [ [[MIN_VAL_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i64, ptr [[SRC]], i64 [[IV]]
+; CHECK-NEXT:    [[L:%.*]] = load i64, ptr [[GEP]], align 4
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i64 [[SCALAR_RECUR]], [[L]]
+; CHECK-NEXT:    [[MIN_VAL_NEXT]] = add i64 [[L]], 1
+; CHECK-NEXT:    [[FOO:%.*]] = call i64 @llvm.umin.i64(i64 [[SCALAR_RECUR]], i64 [[L]])
+; CHECK-NEXT:    [[MIN_IDX_NEXT]] = select i1 [[CMP]], i64 [[IV]], i64 [[MIN_IDX]]
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
+; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[IV_NEXT]], 0
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[EXIT]], label [[LOOP]], !llvm.loop [[LOOP5:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[RES:%.*]] = phi i64 [ [[MIN_IDX_NEXT]], [[LOOP]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    ret i64 [[RES]]
 ;
 entry:
   br label %loop
 
 loop:
   %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
   %min.idx = phi i64 [ 0, %entry ], [ %min.idx.next, %loop ]
   %min.val = phi i64 [ 0, %entry ], [ %min.val.next, %loop ]

llvm/test/Transforms/LoopVectorize/smax-idx.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=loop-vectorize -force-vector-width=4 -debug-only=loop-vectorize,iv-descriptors -S < %s 2>&1 | FileCheck %s
+
+define i64 @smax_idx(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[N:%.*]], 4
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[N]], 4
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[N]], [[N_MOD_VF]]
+; CHECK-NEXT:    [[MINMAX_IDENT_SPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[MM:%.*]], i64 0
+; CHECK-NEXT:    [[MINMAX_IDENT_SPLAT:%.*]] = shufflevector <4 x i64> [[MINMAX_IDENT_SPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i64> <i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808>, i64 [[II:%.*]], i32 0
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i64> [ [[MINMAX_IDENT_SPLAT]], [[VECTOR_PH]] ], [ [[TMP4:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x i64> [ [[TMP0]], [[VECTOR_PH]] ], [ [[TMP6:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i64, ptr [[A:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds i64, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i64>, ptr [[TMP3]], align 4
+; CHECK-NEXT:    [[TMP4]] = call <4 x i64> @llvm.smax.v4i64(<4 x i64> [[VEC_PHI]], <4 x i64> [[WIDE_LOAD]])
+; CHECK-NEXT:    [[TMP5:%.*]] = icmp slt <4 x i64> [[VEC_PHI]], [[WIDE_LOAD]]
+; CHECK-NEXT:    [[TMP6]] = select <4 x i1> [[TMP5]], <4 x i64> [[VEC_IND]], <4 x i64> [[VEC_PHI1]]
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i64> [[VEC_IND]], <i64 4, i64 4, i64 4, i64 4>
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[TMP8:%.*]] = call i64 @llvm.vector.reduce.smax.v4i64(<4 x i64> [[TMP4]])
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[TMP8]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <4 x i64> [[DOTSPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[MASK_CMP:%.*]] = icmp eq <4 x i64> [[DOTSPLAT]], [[TMP4]]
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[N]], [[N_VEC]]
+; CHECK-NEXT:    [[MASK_SELECT:%.*]] = select <4 x i1> [[MASK_CMP]], <4 x i64> [[TMP6]], <4 x i64> <i64 9223372036854775807, i64 9223372036854775807, i64 9223372036854775807, i64 9223372036854775807>
+; CHECK-NEXT:    [[TMP9:%.*]] = call i64 @llvm.vector.reduce.smin.v4i64(<4 x i64> [[MASK_SELECT]])
+; CHECK-NEXT:    [[RDX_SELECT_CMP:%.*]] = icmp ne i64 [[TMP9]], -9223372036854775808
+; CHECK-NEXT:    [[RDX_SELECT:%.*]] = select i1 [[RDX_SELECT_CMP]], i64 [[TMP9]], i64 [[II]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i64 [ [[MM]], [[ENTRY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX2:%.*]] = phi i64 [ [[II]], [[ENTRY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[MAX_09:%.*]] = phi i64 [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[TMP11:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[IDX_011:%.*]] = phi i64 [ [[BC_MERGE_RDX2]], [[SCALAR_PH]] ], [ [[SPEC_SELECT7:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i64, ptr [[A]], i64 [[INDVARS_IV]]
+; CHECK-NEXT:    [[TMP10:%.*]] = load i64, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT:    [[TMP11]] = tail call i64 @llvm.smax.i64(i64 [[MAX_09]], i64 [[TMP10]])
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i64 [[MAX_09]], [[TMP10]]
+; CHECK-NEXT:    [[SPEC_SELECT7]] = select i1 [[CMP1]], i64 [[INDVARS_IV]], i64 [[IDX_011]]
+; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
+; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[N]]
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[EXIT]], label [[FOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi i64 [ [[TMP11]], [[FOR_BODY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[SPEC_SELECT7_LCSSA:%.*]] = phi i64 [ [[SPEC_SELECT7]], [[FOR_BODY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    store i64 [[DOTLCSSA]], ptr [[RES_MAX:%.*]], align 4
+; CHECK-NEXT:    ret i64 [[SPEC_SELECT7_LCSSA]]
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; Check the different order of reduction phis.
+;
+define i64 @smax_idx_inverted_phi(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_inverted_phi(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[N:%.*]], 4
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[N]], 4
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[N]], [[N_MOD_VF]]
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i64> <i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808>, i64 [[II:%.*]], i32 0
+; CHECK-NEXT:    [[MINMAX_IDENT_SPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[MM:%.*]], i64 0
+; CHECK-NEXT:    [[MINMAX_IDENT_SPLAT:%.*]] = shufflevector <4 x i64> [[MINMAX_IDENT_SPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i64> [ [[TMP0]], [[VECTOR_PH]] ], [ [[TMP6:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x i64> [ [[MINMAX_IDENT_SPLAT]], [[VECTOR_PH]] ], [ [[TMP4:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i64, ptr [[A:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds i64, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i64>, ptr [[TMP3]], align 4
+; CHECK-NEXT:    [[TMP4]] = call <4 x i64> @llvm.smax.v4i64(<4 x i64> [[VEC_PHI1]], <4 x i64> [[WIDE_LOAD]])
+; CHECK-NEXT:    [[TMP5:%.*]] = icmp slt <4 x i64> [[VEC_PHI1]], [[WIDE_LOAD]]
+; CHECK-NEXT:    [[TMP6]] = select <4 x i1> [[TMP5]], <4 x i64> [[VEC_IND]], <4 x i64> [[VEC_PHI]]
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i64> [[VEC_IND]], <i64 4, i64 4, i64 4, i64 4>
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[TMP8:%.*]] = call i64 @llvm.vector.reduce.smax.v4i64(<4 x i64> [[TMP4]])
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[TMP8]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <4 x i64> [[DOTSPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[MASK_CMP:%.*]] = icmp eq <4 x i64> [[DOTSPLAT]], [[TMP4]]
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[N]], [[N_VEC]]
+; CHECK-NEXT:    [[MASK_SELECT:%.*]] = select <4 x i1> [[MASK_CMP]], <4 x i64> [[TMP6]], <4 x i64> <i64 9223372036854775807, i64 9223372036854775807, i64 9223372036854775807, i64 9223372036854775807>
+; CHECK-NEXT:    [[TMP9:%.*]] = call i64 @llvm.vector.reduce.smin.v4i64(<4 x i64> [[MASK_SELECT]])
+; CHECK-NEXT:    [[RDX_SELECT_CMP:%.*]] = icmp ne i64 [[TMP9]], -9223372036854775808
+; CHECK-NEXT:    [[RDX_SELECT:%.*]] = select i1 [[RDX_SELECT_CMP]], i64 [[TMP9]], i64 [[II]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i64 [ [[MM]], [[ENTRY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX2:%.*]] = phi i64 [ [[II]], [[ENTRY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[IDX_011:%.*]] = phi i64 [ [[BC_MERGE_RDX2]], [[SCALAR_PH]] ], [ [[SPEC_SELECT7:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[MAX_09:%.*]] = phi i64 [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[TMP11:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i64, ptr [[A]], i64 [[INDVARS_IV]]
+; CHECK-NEXT:    [[TMP10:%.*]] = load i64, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT:    [[TMP11]] = tail call i64 @llvm.smax.i64(i64 [[MAX_09]], i64 [[TMP10]])
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i64 [[MAX_09]], [[TMP10]]
+; CHECK-NEXT:    [[SPEC_SELECT7]] = select i1 [[CMP1]], i64 [[INDVARS_IV]], i64 [[IDX_011]]
+; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
+; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[N]]
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[EXIT]], label [[FOR_BODY]], !llvm.loop [[LOOP5:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi i64 [ [[TMP11]], [[FOR_BODY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[SPEC_SELECT7_LCSSA:%.*]] = phi i64 [ [[SPEC_SELECT7]], [[FOR_BODY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    store i64 [[DOTLCSSA]], ptr [[RES_MAX:%.*]], align 4
+; CHECK-NEXT:    ret i64 [[SPEC_SELECT7_LCSSA]]
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]  ;;
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]              ;;
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+; Check if it is a MMI when smax is not used outside the loop.
+;
+; Currently at the end, it will check if smax has exitInstruction.
+; But in fact MMI should be possible to use the exitInstruction of
+; SelectICmp be the exitInstruction.
+;
+define i64 @smax_idx_max_no_exit_user(ptr nocapture readonly %a, i64 %mm, i64 %ii, i64 %n) {
+; CHECK-LABEL: @smax_idx_max_no_exit_user(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  ; %1 has no external users
+  ret i64 %spec.select7
+}
+
+; Check smax implemented in terms of select(cmp()).
+;
+; Currently SelectICmp does not support icmp with multiple users.
+; It may be possible to reuse some of the methods in Combination pass to check
+; whether icmp can be copied.
+;
+define i64 @smax_idx_select_cmp(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_select_cmp(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %spec.select, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %cmp1 = icmp slt i64 %max.09, %0                     ;;
+  %spec.select = select i1 %cmp1, i64 %0, i64 %max.09  ;;
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %spec.select, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; Check sge case.
+;
+define i64 @smax_idx_inverted_pred(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_inverted_pred(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[N:%.*]], 4
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[N]], 4
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[N]], [[N_MOD_VF]]
+; CHECK-NEXT:    [[MINMAX_IDENT_SPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[MM:%.*]], i64 0
+; CHECK-NEXT:    [[MINMAX_IDENT_SPLAT:%.*]] = shufflevector <4 x i64> [[MINMAX_IDENT_SPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i64> <i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808>, i64 [[II:%.*]], i32 0
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i64> [ [[MINMAX_IDENT_SPLAT]], [[VECTOR_PH]] ], [ [[TMP4:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x i64> [ [[TMP0]], [[VECTOR_PH]] ], [ [[TMP6:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i64, ptr [[A:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds i64, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i64>, ptr [[TMP3]], align 4
+; CHECK-NEXT:    [[TMP4]] = call <4 x i64> @llvm.smax.v4i64(<4 x i64> [[VEC_PHI]], <4 x i64> [[WIDE_LOAD]])
+; CHECK-NEXT:    [[TMP5:%.*]] = icmp sge <4 x i64> [[WIDE_LOAD]], [[VEC_PHI]]
+; CHECK-NEXT:    [[TMP6]] = select <4 x i1> [[TMP5]], <4 x i64> [[VEC_IND]], <4 x i64> [[VEC_PHI1]]
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i64> [[VEC_IND]], <i64 4, i64 4, i64 4, i64 4>
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[TMP8:%.*]] = call i64 @llvm.vector.reduce.smax.v4i64(<4 x i64> [[TMP4]])
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[TMP8]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <4 x i64> [[DOTSPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[MASK_CMP:%.*]] = icmp eq <4 x i64> [[DOTSPLAT]], [[TMP4]]
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[N]], [[N_VEC]]
+; CHECK-NEXT:    [[MASK_SELECT:%.*]] = select <4 x i1> [[MASK_CMP]], <4 x i64> [[TMP6]], <4 x i64> <i64 9223372036854775807, i64 9223372036854775807, i64 9223372036854775807, i64 9223372036854775807>
+; CHECK-NEXT:    [[TMP9:%.*]] = call i64 @llvm.vector.reduce.smin.v4i64(<4 x i64> [[MASK_SELECT]])
+; CHECK-NEXT:    [[RDX_SELECT_CMP:%.*]] = icmp ne i64 [[TMP9]], -9223372036854775808
+; CHECK-NEXT:    [[RDX_SELECT:%.*]] = select i1 [[RDX_SELECT_CMP]], i64 [[TMP9]], i64 [[II]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i64 [ [[MM]], [[ENTRY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX2:%.*]] = phi i64 [ [[II]], [[ENTRY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[MAX_09:%.*]] = phi i64 [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[TMP11:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[IDX_011:%.*]] = phi i64 [ [[BC_MERGE_RDX2]], [[SCALAR_PH]] ], [ [[SPEC_SELECT7:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i64, ptr [[A]], i64 [[INDVARS_IV]]
+; CHECK-NEXT:    [[TMP10:%.*]] = load i64, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT:    [[TMP11]] = tail call i64 @llvm.smax.i64(i64 [[MAX_09]], i64 [[TMP10]])
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp sge i64 [[TMP10]], [[MAX_09]]
+; CHECK-NEXT:    [[SPEC_SELECT7]] = select i1 [[CMP1]], i64 [[INDVARS_IV]], i64 [[IDX_011]]
+; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
+; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[N]]
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[EXIT]], label [[FOR_BODY]], !llvm.loop [[LOOP7:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi i64 [ [[TMP11]], [[FOR_BODY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[SPEC_SELECT7_LCSSA:%.*]] = phi i64 [ [[SPEC_SELECT7]], [[FOR_BODY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    store i64 [[DOTLCSSA]], ptr [[RES_MAX:%.*]], align 4
+; CHECK-NEXT:    ret i64 [[SPEC_SELECT7_LCSSA]]
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp sge i64 %0, %max.09  ;;
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; In such cases, the last index should be extracted.
+;
+define i64 @smax_idx_extract_last(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_extract_last(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[N:%.*]], 4
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       vector.ph:
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 [[N]], 4
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 [[N]], [[N_MOD_VF]]
+; CHECK-NEXT:    [[MINMAX_IDENT_SPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[MM:%.*]], i64 0
+; CHECK-NEXT:    [[MINMAX_IDENT_SPLAT:%.*]] = shufflevector <4 x i64> [[MINMAX_IDENT_SPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <4 x i64> <i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808>, i64 [[II:%.*]], i32 0
+; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
+; CHECK:       vector.body:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_IND:%.*]] = phi <4 x i64> [ <i64 0, i64 1, i64 2, i64 3>, [[VECTOR_PH]] ], [ [[VEC_IND_NEXT:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i64> [ [[MINMAX_IDENT_SPLAT]], [[VECTOR_PH]] ], [ [[TMP4:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI1:%.*]] = phi <4 x i64> [ [[TMP0]], [[VECTOR_PH]] ], [ [[TMP6:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i64, ptr [[A:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds i64, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <4 x i64>, ptr [[TMP3]], align 4
+; CHECK-NEXT:    [[TMP4]] = call <4 x i64> @llvm.smax.v4i64(<4 x i64> [[VEC_PHI]], <4 x i64> [[WIDE_LOAD]])
+; CHECK-NEXT:    [[TMP5:%.*]] = icmp sgt <4 x i64> [[VEC_PHI]], [[WIDE_LOAD]]
+; CHECK-NEXT:    [[TMP6]] = select <4 x i1> [[TMP5]], <4 x i64> [[VEC_PHI1]], <4 x i64> [[VEC_IND]]
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
+; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i64> [[VEC_IND]], <i64 4, i64 4, i64 4, i64 4>
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP7]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
+; CHECK:       middle.block:
+; CHECK-NEXT:    [[TMP8:%.*]] = call i64 @llvm.vector.reduce.smax.v4i64(<4 x i64> [[TMP4]])
+; CHECK-NEXT:    [[DOTSPLATINSERT:%.*]] = insertelement <4 x i64> poison, i64 [[TMP8]], i64 0
+; CHECK-NEXT:    [[DOTSPLAT:%.*]] = shufflevector <4 x i64> [[DOTSPLATINSERT]], <4 x i64> poison, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[MASK_CMP:%.*]] = icmp eq <4 x i64> [[DOTSPLAT]], [[TMP4]]
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[N]], [[N_VEC]]
+; CHECK-NEXT:    [[MASK_SELECT:%.*]] = select <4 x i1> [[MASK_CMP]], <4 x i64> [[TMP6]], <4 x i64> <i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808, i64 -9223372036854775808>
+; CHECK-NEXT:    [[TMP9:%.*]] = call i64 @llvm.vector.reduce.smax.v4i64(<4 x i64> [[MASK_SELECT]])
+; CHECK-NEXT:    [[RDX_SELECT_CMP:%.*]] = icmp ne i64 [[TMP9]], -9223372036854775808
+; CHECK-NEXT:    [[RDX_SELECT:%.*]] = select i1 [[RDX_SELECT_CMP]], i64 [[TMP9]], i64 [[II]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
+; CHECK:       scalar.ph:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX:%.*]] = phi i64 [ [[MM]], [[ENTRY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[BC_MERGE_RDX2:%.*]] = phi i64 [ [[II]], [[ENTRY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[MAX_09:%.*]] = phi i64 [ [[BC_MERGE_RDX]], [[SCALAR_PH]] ], [ [[TMP11:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[IDX_011:%.*]] = phi i64 [ [[BC_MERGE_RDX2]], [[SCALAR_PH]] ], [ [[SPEC_SELECT7:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i64, ptr [[A]], i64 [[INDVARS_IV]]
+; CHECK-NEXT:    [[TMP10:%.*]] = load i64, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT:    [[TMP11]] = tail call i64 @llvm.smax.i64(i64 [[MAX_09]], i64 [[TMP10]])
+; CHECK-NEXT:    [[CMP1_NOT:%.*]] = icmp sgt i64 [[MAX_09]], [[TMP10]]
+; CHECK-NEXT:    [[SPEC_SELECT7]] = select i1 [[CMP1_NOT]], i64 [[IDX_011]], i64 [[INDVARS_IV]]
+; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
+; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[N]]
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[EXIT]], label [[FOR_BODY]], !llvm.loop [[LOOP9:![0-9]+]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[DOTLCSSA:%.*]] = phi i64 [ [[TMP11]], [[FOR_BODY]] ], [ [[TMP8]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[SPEC_SELECT7_LCSSA:%.*]] = phi i64 [ [[SPEC_SELECT7]], [[FOR_BODY]] ], [ [[RDX_SELECT]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    store i64 [[DOTLCSSA]], ptr [[RES_MAX:%.*]], align 4
+; CHECK-NEXT:    ret i64 [[SPEC_SELECT7_LCSSA]]
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1.not = icmp sgt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1.not, i64 %idx.011, i64 %indvars.iv
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; The operands of smax intrinsic and icmp are not the same to be recognized as MMI.
+;
+; FIXME: this case should not be vectorized. We have to check the operands of intrinsic and icmp.
+define i64 @smax_idx_not_vec_1(ptr nocapture readonly %a, ptr nocapture readonly %b, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_not_vec_1(
+; CHECK-NOT:   vector.body:
+;
+  entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %2, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %arrayidx.01 = getelementptr inbounds i64, ptr %b, i64 %indvars.iv
+  %1 = load i64, ptr %arrayidx
+  %2 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %1  ;;
+  %spec.select7 = select i1 %cmp1, i64 %indvars.iv, i64 %idx.011
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %2, ptr %res_max
+  ret i64 %spec.select7
+}
+
+;
+; It cannot be recognized as MMI when the operand of index select is not an induction variable.
+;
+define i64 @smax_idx_not_vec_2(ptr nocapture readonly %a, i64 %mm, i64 %ii, ptr nocapture writeonly %res_max, i64 %n) {
+; CHECK-LABEL: @smax_idx_not_vec_2(
+; CHECK-NOT:   vector.body:
+;
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %max.09 = phi i64 [ %mm, %entry ], [ %1, %for.body ]
+  %idx.011 = phi i64 [ %ii, %entry ], [ %spec.select7, %for.body ]
+  %arrayidx = getelementptr inbounds i64, ptr %a, i64 %indvars.iv
+  %0 = load i64, ptr %arrayidx
+  %1 = tail call i64 @llvm.smax.i64(i64 %max.09, i64 %0)
+  %cmp1 = icmp slt i64 %max.09, %0
+  %spec.select7 = select i1 %cmp1, i64 123, i64 %idx.011  ;;
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, %n
+  br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+  store i64 %1, ptr %res_max
+  ret i64 %spec.select7
+}
+
+declare i64 @llvm.smax.i64(i64, i64)