[VectorCombine] fold extract-extract-op with different extraction indexes

[spatel]

Summary

opcode (extelt V0, Ext0), (ext V1, Ext1) --> extelt (opcode (splat V0, Ext0), V1), Ext1

The first part of this patch generalizes the cost calculation to accept different extraction indexes. The second part creates a shuffle+extract before feeding into the existing code to create a vector op+extract.

The patch conservatively uses "TargetTransformInfo::SK_PermuteSingleSrc" rather than "TargetTransformInfo::SK_Broadcast" (splat specifically from element 0) because we do not have a more general "SK_Splat" currently. That does not affect any of the current regression tests, but we might be able to find some cost model target specialization where that comes into play.

I suspect that we can expose some missing x86 horizontal op codegen with this transform, so I'm speculatively adding a debug flag to disable the binop variant of this transform to allow easier testing.

The test changes show that we're sensitive to cost model diffs (as we should be), so that means that patches like D74976 should have better coverage.

[RKSimon]

getShuffleCost already takes an Index value (default = 0) that I meant to use for this kind of thing (its currently just used for subvector insertion/extraction), so either 'tweaking' SK_Broadcast to use Index or replacing it with a SK_Splat mode would be relatively painless.

[lebedev.ri]

Taking a step back, we have

; 0. scalar
%e0 = extractelement %x, C0
%e1 = extractelement %y, C1
%r = op %e0, %e1

Let's focus on C0 != C1 problem, i see three general approaches there:

1. move either one lane to another lane
   1. move lane C0 to lane C1
   2. move lane C1 to lane C0
2. move both lanes into lane 0

In current solution, why do we decide to only entertain the idea of replacing the costlier extract?
Don't we want to check all three variants? (there's some overlap if one of C0,C1 is already lane 0)
What if the other extract is from lane 0? We'd then be able to use TTI::SK_Broadcast.

llvm/lib/Transforms/Vectorize/VectorCombine.cpp

120

s/1/one/, else it's ambitious with 'first'

[spatel]

In D75689#1907966, @lebedev.ri wrote:

Taking a step back, we have

; 0. scalar
%e0 = extractelement %x, C0
%e1 = extractelement %y, C1
%r = op %e0, %e1

Let's focus on C0 != C1 problem, i see three general approaches there:

1. move either one lane to another lane
   1. move lane C0 to lane C1
   2. move lane C1 to lane C0
2. move both lanes into lane 0

In current solution, why do we decide to only entertain the idea of replacing the costlier extract?
Don't we want to check all three variants? (there's some overlap if one of C0,C1 is already lane 0)
What if the other extract is from lane 0? We'd then be able to use TTI::SK_Broadcast.

Correct - I thought about reversing the operands if it would allow the shuffle to be a broadcast, but didn't try to implement it. My guess is that won't change the costs for the examples shown here (since they don't change even if we incorrectly specify that the shuffle in the current patch is a broadcast).

Similarly, the option where we shuffle both operands to element 0 has potential to be the winner, but I'm skeptical that it would be beneficial on most x86 examples. So I agree that if we want to get the optimal sequence, we need to model all of those possibilities - and by not modeling all of the possibilities, we may be missing an optimization. We could also argue that we're still in IR, so we should select 1 of those forms as semi-canonical and let the backend handle the other transforms.

Ok, if I add a TODO comment for now?

[lebedev.ri]

llvm/lib/Transforms/Vectorize/VectorCombine.cpp

119

So essentially we are assuming that this is the optimal cost model.
Can we assert that?

int ExpensiveExtractCost = std::max(Extract0Cost, Extract1Cost);
(void)ExpensiveExtractCost;

// FIXME: introduce TargetTransformInfo::SK_Splat.
assert(TTI.getShuffleCost(TargetTransformInfo::SK_PermuteSingleSrc, VecTy) + CheapExtractCost
       <=
       TTI.getShuffleCost(TargetTransformInfo::SK_Broadcast, VecTy) + ExpensiveExtractCost
);

[lebedev.ri]

Ok, after looking at this more, i think any further improvements (less pessimistic cost computations)
will look really awkward without first abstracting away the splat shuffle cost,
I think it would be okay to add FIXME's for now.

@RKSimon thoughts?

llvm/lib/Transforms/Vectorize/VectorCombine.cpp

89–90

// FIXME: evaluate whether that always results in lowest cost

119

Err, that won't really do it i guess, so let's not do that.

[RKSimon]

LGTM - You might want to add some test cases with 256/512-bit vectors (with indices coming from the same/different 128-bit subvectors) as well to get a broader range of extraction costs.

I'm not certain a SK_Splat will make much difference - the shuffle masks with a single non-undef index would be in most cases a lot cheaper even than that, especially on early SSE targets, so maybe we need to either consider another shuffle enum type or just provide the ability to compute costs from raw shuffle masks?

[spatel]

In D75689#1909516, @RKSimon wrote:

LGTM - You might want to add some test cases with 256/512-bit vectors (with indices coming from the same/different 128-bit subvectors) as well to get a broader range of extraction costs.

Yes, will add some larger vector tests.

I'm not certain a SK_Splat will make much difference - the shuffle masks with a single non-undef index would be in most cases a lot cheaper even than that, especially on early SSE targets, so maybe we need to either consider another shuffle enum type or just provide the ability to compute costs from raw shuffle masks?

There's no clear answer on how far we should take the modeling. We've said in the past that we shouldn't try that hard -- because this is IR, we can never know exactly how it will be lowered for every target.
The idea of trying different options and picking a winner sounds like VPlan to me (I haven't kept up with its current state, so need to review that.)

[jgorbe]

Hi,

We're seeing some large performance regressions on Eigen (http://eigen.tuxfamily.org/) running on haswell and skylake machines with this patch. Could you please revert it?

[lebedev.ri]

In D75689#1925667, @jgorbe wrote:

Hi,

We're seeing some large performance regressions on Eigen (http://eigen.tuxfamily.org/) running on haswell and skylake machines with this patch.

Those are being compiled with the correct -march= for the machine that actually runs benchmarks, right?
Can you be more specific? Reproduction steps (which benchmark specifically), perhaps some regressed snippets?

Could you please revert it?

[spatel]

In D75689#1925667, @jgorbe wrote:

Could you please revert it?

I'd prefer more specific reproduction steps before we make changes here. Ideally, please file a bug report with a reduced example.
Also, as noted in the description/commit message, I expected that this patch could cause perf problems, so there are debug options to help narrow those down:

{-mllvm } -disable-binop-extract-shuffle / -disable-vector-combine

If we can use those (or even add more specific flags) to temporarily disable functionality while investigating, that would be more efficient than reverting.

[jgorbe]

Thanks for the note about the flags. We have tried both of them, and any (or both) of them being present causes the regression to go away, so that unblocks us while we work on producing a proper test case.

[spatel]

In D75689#1927928, @jgorbe wrote:

Thanks for the note about the flags. We have tried both of them, and any (or both) of them being present causes the regression to go away, so that unblocks us while we work on producing a proper test case.

Sounds good. Note that "-disable-vector-combine" is the big hammer; it effectively disables this entire pass.
If the regressions only appeared with this patch and go away with "-disable-binop-extract-shuffle", the most likely source of the problem is the cost model or this pass is interacting badly with the SLP vectorizer.

llvm/lib/Transforms/Vectorize/VectorCombine.cpp

 #define DEBUG_TYPE "vector-combine"
 STATISTIC(NumVecCmp, "Number of vector compares formed");
 STATISTIC(NumVecBO, "Number of vector binops formed");
 
 static cl::opt<bool> DisableVectorCombine(
     "disable-vector-combine", cl::init(false), cl::Hidden,
     cl::desc("Disable all vector combine transforms"));
 
-/// Compare the relative costs of extracts followed by scalar operation vs.
-/// vector operation followed by extract:
-/// opcode (extelt V0, C), (extelt V1, C) --> extelt (opcode V0, V1), C
-/// Unless the vector op is much more expensive than the scalar op, this
-/// eliminates an extract.
+static cl::opt<bool> DisableBinopExtractShuffle(
+    "disable-binop-extract-shuffle", cl::init(false), cl::Hidden,
+    cl::desc("Disable binop extract to shuffle transforms"));
+
+
+/// Compare the relative costs of 2 extracts followed by scalar operation vs.
+/// vector operation(s) followed by extract. Return true if the existing
+/// instructions are cheaper than a vector alternative. Otherwise, return false
+/// and if one of the extracts should be transformed to a shufflevector, set
+/// \p ConvertToShuffle to that extract instruction.
 static bool isExtractExtractCheap(Instruction *Ext0, Instruction *Ext1,
                                   unsigned Opcode,
-                                  const TargetTransformInfo &TTI) {
+                                  const TargetTransformInfo &TTI,
+                                  Instruction *&ConvertToShuffle) {
   assert(isa<ConstantInt>(Ext0->getOperand(1)) &&
-         (cast<ConstantInt>(Ext0->getOperand(1))->getZExtValue() ==
-          cast<ConstantInt>(Ext1->getOperand(1))->getZExtValue()) &&
-         "Expected same constant extract index");
-
+         isa<ConstantInt>(Ext1->getOperand(1)) &&
+         "Expected constant extract indexes");
   Type *ScalarTy = Ext0->getType();
   Type *VecTy = Ext0->getOperand(0)->getType();
   int ScalarOpCost, VectorOpCost;
 
   // Get cost estimates for scalar and vector versions of the operation.
   bool IsBinOp = Instruction::isBinaryOp(Opcode);
   if (IsBinOp) {
     ScalarOpCost = TTI.getArithmeticInstrCost(Opcode, ScalarTy);
     VectorOpCost = TTI.getArithmeticInstrCost(Opcode, VecTy);
   } else {
     assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) &&
            "Expected a compare");
     ScalarOpCost = TTI.getCmpSelInstrCost(Opcode, ScalarTy,
                                           CmpInst::makeCmpResultType(ScalarTy));
     VectorOpCost = TTI.getCmpSelInstrCost(Opcode, VecTy,
                                           CmpInst::makeCmpResultType(VecTy));
   }
 
-  // Get cost estimate for the extract element. This cost will factor into
+  // Get cost estimates for the extract elements. These costs will factor into
   // both sequences.
-  unsigned ExtIndex = cast<ConstantInt>(Ext0->getOperand(1))->getZExtValue();
-  int ExtractCost = TTI.getVectorInstrCost(Instruction::ExtractElement,
-                                           VecTy, ExtIndex);
+  unsigned Ext0Index = cast<ConstantInt>(Ext0->getOperand(1))->getZExtValue();
+  unsigned Ext1Index = cast<ConstantInt>(Ext1->getOperand(1))->getZExtValue();
+
+  int Extract0Cost = TTI.getVectorInstrCost(Instruction::ExtractElement,
+                                            VecTy, Ext0Index);
+  int Extract1Cost = TTI.getVectorInstrCost(Instruction::ExtractElement,
+                                            VecTy, Ext1Index);
+
+  // A more expensive extract will always be replaced by a splat shuffle.
+  // For example, if Ext0 is more expensive:
+  // opcode (extelt V0, Ext0), (ext V1, Ext1) -->
+  // extelt (opcode (splat V0, Ext0), V1), Ext1
+  int CheapExtractCost = std::min(Extract0Cost, Extract1Cost);
 
   // Extra uses of the extracts mean that we include those costs in the
   // vector total because those instructions will not be eliminated.
   int OldCost, NewCost;
-  if (Ext0->getOperand(0) == Ext1->getOperand(0)) {
-    // Handle a special case. If the 2 operands are identical, adjust the
+  if (Ext0->getOperand(0) == Ext1->getOperand(0) && Ext0Index == Ext1Index) {
+    // Handle a special case. If the 2 extracts are identical, adjust the
     // formulas to account for that. The extra use charge allows for either the
     // CSE'd pattern or an unoptimized form with identical values:
     // opcode (extelt V, C), (extelt V, C) --> extelt (opcode V, V), C
     bool HasUseTax = Ext0 == Ext1 ? !Ext0->hasNUses(2)
                                   : !Ext0->hasOneUse() || !Ext1->hasOneUse();
-    OldCost = ExtractCost + ScalarOpCost;
-    NewCost = VectorOpCost + ExtractCost + HasUseTax * ExtractCost;
+    OldCost = CheapExtractCost + ScalarOpCost;
+    NewCost = VectorOpCost + CheapExtractCost + HasUseTax * CheapExtractCost;
   } else {
     // Handle the general case. Each extract is actually a different value:
-    // opcode (extelt V0, C), (extelt V1, C) --> extelt (opcode V0, V1), C
-    OldCost = 2 * ExtractCost + ScalarOpCost;
-    NewCost = VectorOpCost + ExtractCost + !Ext0->hasOneUse() * ExtractCost +
-              !Ext1->hasOneUse() * ExtractCost;
+    // opcode (extelt V0, C0), (extelt V1, C1) --> extelt (opcode V0, V1), C
+    OldCost = Extract0Cost + Extract1Cost + ScalarOpCost;
+    NewCost = VectorOpCost + CheapExtractCost +
+              !Ext0->hasOneUse() * Extract0Cost +
+              !Ext1->hasOneUse() * Extract1Cost;
+  }
+
+  if (Ext0Index == Ext1Index) {
+    // If the extract indexes are identical, no shuffle is needed.
+    ConvertToShuffle = nullptr;
+  } else {
+    if (IsBinOp && DisableBinopExtractShuffle)
+      return true;
+
+    // If we are extracting from 2 different indexes, then 1 operand must be
+    // shuffled before performing the vector operation. The shuffle mask is
+    // undefined except for 1 lane that is being translated to the remaining
+    // extraction lane. Therefore, it is a splat shuffle. Ex:
+    // ShufMask = { undef, undef, 0, undef }
+    // TODO: The cost model has an option for a "broadcast" shuffle
+    //       (splat-from-element-0), but no option for a more general splat.
+    NewCost +=
+        TTI.getShuffleCost(TargetTransformInfo::SK_PermuteSingleSrc, VecTy);
+
+    // The more expensive extract will be replaced by a shuffle. If the extracts
+    // have the same cost, replace the extract with the higher index.
+    if (Extract0Cost > Extract1Cost)
+      ConvertToShuffle = Ext0;
+    else if (Extract1Cost > Extract0Cost)
+      ConvertToShuffle = Ext1;
+    else
+      ConvertToShuffle = Ext0Index > Ext1Index ? Ext0 : Ext1;
   }
+
   // Aggressively form a vector op if the cost is equal because the transform
   // may enable further optimization.
   // Codegen can reverse this transform (scalarize) if it was not profitable.
   return OldCost < NewCost;
 }
 
 /// Try to reduce extract element costs by converting scalar compares to vector
 /// compares followed by extract.
static bool foldExtractExtract(Instruction &I, const TargetTransformInfo &TTI) {
 
   Value *V0, *V1;
   uint64_t C0, C1;
   if (!match(Ext0, m_ExtractElement(m_Value(V0), m_ConstantInt(C0))) ||
       !match(Ext1, m_ExtractElement(m_Value(V1), m_ConstantInt(C1))) ||
       V0->getType() != V1->getType())
     return false;
 
-  // TODO: Handle C0 != C1 by shuffling 1 of the operands.
-  if (C0 != C1)
+  Instruction *ConvertToShuffle;
+  if (isExtractExtractCheap(Ext0, Ext1, I.getOpcode(), TTI, ConvertToShuffle))
     return false;
 
-  if (isExtractExtractCheap(Ext0, Ext1, I.getOpcode(), TTI))
-    return false;
+  if (ConvertToShuffle) {
+    // The shuffle mask is undefined except for 1 lane that is being translated
+    // to the cheap extraction lane. Example:
+    // ShufMask = { 2, undef, undef, undef }
+    uint64_t SplatIndex = ConvertToShuffle == Ext0 ? C0 : C1;
+    uint64_t CheapExtIndex = ConvertToShuffle == Ext0 ? C1 : C0;
+    Type *VecTy = V0->getType();
+    Type *I32Ty = IntegerType::getInt32Ty(I.getContext());
+    UndefValue *Undef = UndefValue::get(I32Ty);
+    SmallVector<Constant *, 32> ShufMask(VecTy->getVectorNumElements(), Undef);
+    ShufMask[CheapExtIndex] = ConstantInt::get(I32Ty, SplatIndex);
+    IRBuilder<> Builder(ConvertToShuffle);
+
+    // extelt X, C --> extelt (splat X), C'
+    Value *Shuf = Builder.CreateShuffleVector(ConvertToShuffle->getOperand(0),
+                                              UndefValue::get(VecTy),
+                                              ConstantVector::get(ShufMask));
+    Value *NewExt = Builder.CreateExtractElement(Shuf, CheapExtIndex);
+    if (ConvertToShuffle == Ext0)
+      Ext0 = cast<Instruction>(NewExt);
+    else
+      Ext1 = cast<Instruction>(NewExt);
+  }
 
   if (Pred != CmpInst::BAD_ICMP_PREDICATE)
     foldExtExtCmp(Ext0, Ext1, I, TTI);
   else
     foldExtExtBinop(Ext0, Ext1, I, TTI);
 
   return true;
 }

llvm/test/Transforms/VectorCombine/X86/extract-binop.ll

 ;
   %e0 = extractelement <16 x i8> %x, i32 0
   %e1 = extractelement <16 x i8> %y, i32 0
   call void @use_i8(i8 %e1)
   %r = add i8 %e0, %e1
   ret i8 %r
 }
 
-; TODO: Different extract indexes requires a shuffle.
-
 define i8 @ext0_ext1_add(<16 x i8> %x, <16 x i8> %y) {
-; CHECK-LABEL: @ext0_ext1_add(
-; CHECK-NEXT:    [[E0:%.*]] = extractelement <16 x i8> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[E1:%.*]] = extractelement <16 x i8> [[Y:%.*]], i32 1
-; CHECK-NEXT:    [[R:%.*]] = add nuw i8 [[E0]], [[E1]]
-; CHECK-NEXT:    ret i8 [[R]]
+; SSE-LABEL: @ext0_ext1_add(
+; SSE-NEXT:    [[E0:%.*]] = extractelement <16 x i8> [[X:%.*]], i32 0
+; SSE-NEXT:    [[E1:%.*]] = extractelement <16 x i8> [[Y:%.*]], i32 1
+; SSE-NEXT:    [[R:%.*]] = add nuw i8 [[E0]], [[E1]]
+; SSE-NEXT:    ret i8 [[R]]
+;
+; AVX-LABEL: @ext0_ext1_add(
+; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <16 x i8> [[Y:%.*]], <16 x i8> undef, <16 x i32> <i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
+; AVX-NEXT:    [[TMP2:%.*]] = add nuw <16 x i8> [[X:%.*]], [[TMP1]]
+; AVX-NEXT:    [[TMP3:%.*]] = extractelement <16 x i8> [[TMP2]], i32 0
+; AVX-NEXT:    ret i8 [[TMP3]]
 ;
   %e0 = extractelement <16 x i8> %x, i32 0
   %e1 = extractelement <16 x i8> %y, i32 1
   %r = add nuw i8 %e0, %e1
   ret i8 %r
 }
 
 define i8 @ext5_ext0_add(<16 x i8> %x, <16 x i8> %y) {
-; CHECK-LABEL: @ext5_ext0_add(
-; CHECK-NEXT:    [[E0:%.*]] = extractelement <16 x i8> [[X:%.*]], i32 5
-; CHECK-NEXT:    [[E1:%.*]] = extractelement <16 x i8> [[Y:%.*]], i32 0
-; CHECK-NEXT:    [[R:%.*]] = sub nsw i8 [[E0]], [[E1]]
-; CHECK-NEXT:    ret i8 [[R]]
+; SSE-LABEL: @ext5_ext0_add(
+; SSE-NEXT:    [[E0:%.*]] = extractelement <16 x i8> [[X:%.*]], i32 5
+; SSE-NEXT:    [[E1:%.*]] = extractelement <16 x i8> [[Y:%.*]], i32 0
+; SSE-NEXT:    [[R:%.*]] = sub nsw i8 [[E0]], [[E1]]
+; SSE-NEXT:    ret i8 [[R]]
+;
+; AVX-LABEL: @ext5_ext0_add(
+; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <16 x i8> [[X:%.*]], <16 x i8> undef, <16 x i32> <i32 5, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
+; AVX-NEXT:    [[TMP2:%.*]] = sub nsw <16 x i8> [[TMP1]], [[Y:%.*]]
+; AVX-NEXT:    [[TMP3:%.*]] = extractelement <16 x i8> [[TMP2]], i64 0
+; AVX-NEXT:    ret i8 [[TMP3]]
 ;
   %e0 = extractelement <16 x i8> %x, i32 5
   %e1 = extractelement <16 x i8> %y, i32 0
   %r = sub nsw i8 %e0, %e1
   ret i8 %r
 }
 
 define i8 @ext1_ext6_add(<16 x i8> %x, <16 x i8> %y) {
-; CHECK-LABEL: @ext1_ext6_add(
-; CHECK-NEXT:    [[E0:%.*]] = extractelement <16 x i8> [[X:%.*]], i32 1
-; CHECK-NEXT:    [[E1:%.*]] = extractelement <16 x i8> [[Y:%.*]], i32 6
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[E0]], [[E1]]
-; CHECK-NEXT:    ret i8 [[R]]
+; SSE-LABEL: @ext1_ext6_add(
+; SSE-NEXT:    [[E0:%.*]] = extractelement <16 x i8> [[X:%.*]], i32 1
+; SSE-NEXT:    [[E1:%.*]] = extractelement <16 x i8> [[Y:%.*]], i32 6
+; SSE-NEXT:    [[R:%.*]] = and i8 [[E0]], [[E1]]
+; SSE-NEXT:    ret i8 [[R]]
+;
+; AVX-LABEL: @ext1_ext6_add(
+; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <16 x i8> [[Y:%.*]], <16 x i8> undef, <16 x i32> <i32 undef, i32 6, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
+; AVX-NEXT:    [[TMP2:%.*]] = and <16 x i8> [[X:%.*]], [[TMP1]]
+; AVX-NEXT:    [[TMP3:%.*]] = extractelement <16 x i8> [[TMP2]], i32 1
+; AVX-NEXT:    ret i8 [[TMP3]]
 ;
   %e0 = extractelement <16 x i8> %x, i32 1
   %e1 = extractelement <16 x i8> %y, i32 6
   %r = and i8 %e0, %e1
   ret i8 %r
 }
 
 define float @ext1_ext0_fmul(<4 x float> %x) {
 ; CHECK-LABEL: @ext1_ext0_fmul(
-; CHECK-NEXT:    [[E0:%.*]] = extractelement <4 x float> [[X:%.*]], i32 1
-; CHECK-NEXT:    [[E1:%.*]] = extractelement <4 x float> [[X]], i32 0
-; CHECK-NEXT:    [[R:%.*]] = fmul float [[E0]], [[E1]]
-; CHECK-NEXT:    ret float [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x float> [[X:%.*]], <4 x float> undef, <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
+; CHECK-NEXT:    [[TMP2:%.*]] = fmul <4 x float> [[TMP1]], [[X]]
+; CHECK-NEXT:    [[TMP3:%.*]] = extractelement <4 x float> [[TMP2]], i64 0
+; CHECK-NEXT:    ret float [[TMP3]]
 ;
   %e0 = extractelement <4 x float> %x, i32 1
   %e1 = extractelement <4 x float> %x, i32 0
   %r = fmul float %e0, %e1
   ret float %r
 }
 
 define float @ext0_ext3_fmul_extra_use1(<4 x float> %x) {
 ; CHECK-LABEL: @ext0_ext3_fmul_extra_use1(
 ; CHECK-NEXT:    [[E0:%.*]] = extractelement <4 x float> [[X:%.*]], i32 0
 ; CHECK-NEXT:    call void @use_f32(float [[E0]])
-; CHECK-NEXT:    [[E1:%.*]] = extractelement <4 x float> [[X]], i32 3
-; CHECK-NEXT:    [[R:%.*]] = fmul nnan float [[E0]], [[E1]]
-; CHECK-NEXT:    ret float [[R]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x float> [[X]], <4 x float> undef, <4 x i32> <i32 3, i32 undef, i32 undef, i32 undef>
+; CHECK-NEXT:    [[TMP2:%.*]] = fmul nnan <4 x float> [[X]], [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = extractelement <4 x float> [[TMP2]], i32 0
+; CHECK-NEXT:    ret float [[TMP3]]
 ;
   %e0 = extractelement <4 x float> %x, i32 0
   call void @use_f32(float %e0)
   %e1 = extractelement <4 x float> %x, i32 3
   %r = fmul nnan float %e0, %e1
   ret float %r
 }
 

llvm/test/Transforms/VectorCombine/X86/extract-cmp.ll

t:
   %e = select i1 %cmp2, i32 42, i32 99
   ret i32 %e
 
 f:
   ret i32 0
 }
 
 define i1 @cmp01_v2f64(<2 x double> %x, <2 x double> %y) {
-; CHECK-LABEL: @cmp01_v2f64(
-; CHECK-NEXT:    [[X0:%.*]] = extractelement <2 x double> [[X:%.*]], i32 0
-; CHECK-NEXT:    [[Y1:%.*]] = extractelement <2 x double> [[Y:%.*]], i32 1
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp oge double [[X0]], [[Y1]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; SSE-LABEL: @cmp01_v2f64(
+; SSE-NEXT:    [[X0:%.*]] = extractelement <2 x double> [[X:%.*]], i32 0
+; SSE-NEXT:    [[Y1:%.*]] = extractelement <2 x double> [[Y:%.*]], i32 1
+; SSE-NEXT:    [[CMP:%.*]] = fcmp oge double [[X0]], [[Y1]]
+; SSE-NEXT:    ret i1 [[CMP]]
+;
+; AVX-LABEL: @cmp01_v2f64(
+; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <2 x double> [[Y:%.*]], <2 x double> undef, <2 x i32> <i32 1, i32 undef>
+; AVX-NEXT:    [[TMP2:%.*]] = fcmp oge <2 x double> [[X:%.*]], [[TMP1]]
+; AVX-NEXT:    [[TMP3:%.*]] = extractelement <2 x i1> [[TMP2]], i32 0
+; AVX-NEXT:    ret i1 [[TMP3]]
 ;
   %x0 = extractelement <2 x double> %x, i32 0
   %y1 = extractelement <2 x double> %y, i32 1
   %cmp = fcmp oge double %x0, %y1
   ret i1 %cmp
 }
 
 define i1 @cmp10_v2f64(<2 x double> %x, <2 x double> %y) {
-; CHECK-LABEL: @cmp10_v2f64(
-; CHECK-NEXT:    [[X1:%.*]] = extractelement <2 x double> [[X:%.*]], i32 1
-; CHECK-NEXT:    [[Y0:%.*]] = extractelement <2 x double> [[Y:%.*]], i32 0
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp ule double [[X1]], [[Y0]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; SSE-LABEL: @cmp10_v2f64(
+; SSE-NEXT:    [[X1:%.*]] = extractelement <2 x double> [[X:%.*]], i32 1
+; SSE-NEXT:    [[Y0:%.*]] = extractelement <2 x double> [[Y:%.*]], i32 0
+; SSE-NEXT:    [[CMP:%.*]] = fcmp ule double [[X1]], [[Y0]]
+; SSE-NEXT:    ret i1 [[CMP]]
+;
+; AVX-LABEL: @cmp10_v2f64(
+; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <2 x double> [[X:%.*]], <2 x double> undef, <2 x i32> <i32 1, i32 undef>
+; AVX-NEXT:    [[TMP2:%.*]] = fcmp ule <2 x double> [[TMP1]], [[Y:%.*]]
+; AVX-NEXT:    [[TMP3:%.*]] = extractelement <2 x i1> [[TMP2]], i64 0
+; AVX-NEXT:    ret i1 [[TMP3]]
 ;
   %x1 = extractelement <2 x double> %x, i32 1
   %y0 = extractelement <2 x double> %y, i32 0
   %cmp = fcmp ule double %x1, %y0
   ret i1 %cmp
 }
 
 define i1 @cmp12_v4i32(<4 x i32> %x, <4 x i32> %y) {
 ; CHECK-LABEL: @cmp12_v4i32(
-; CHECK-NEXT:    [[X1:%.*]] = extractelement <4 x i32> [[X:%.*]], i32 1
-; CHECK-NEXT:    [[Y2:%.*]] = extractelement <4 x i32> [[Y:%.*]], i32 2
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[X1]], [[Y2]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i32> [[Y:%.*]], <4 x i32> undef, <4 x i32> <i32 undef, i32 2, i32 undef, i32 undef>
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp sgt <4 x i32> [[X:%.*]], [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = extractelement <4 x i1> [[TMP2]], i32 1
+; CHECK-NEXT:    ret i1 [[TMP3]]
 ;
   %x1 = extractelement <4 x i32> %x, i32 1
   %y2 = extractelement <4 x i32> %y, i32 2
   %cmp = icmp sgt i32 %x1, %y2
   ret i1 %cmp
 }