[InstCombine] Bubble vector.reverse of select operands to their result.

[paulwalker-arm]

Summary

This mirrors a similar shufflevector transformation so the same
effect is obtained for scalable vectors. The transformation is
only performed when it can be proven the number of resulting
reversals is not increased. By bubbling the reversals from operand
to result this should typically be the case and ideally leads to
back-back shuffles that can be elimitated entirely.

[sdesmalen]

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

2350

what is the reasoning behind either of them having a single use?

2353

FValSplat?

[david-arm]

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

2340

Would it be possible to modify one of the existing tests to have flags so we can correctly defend their propagation? We now have code paths where we depend upon the fast-math flags being set correctly on the select by the loop vectoriser.

2354

I don't know how far you want to go with this, but you can support more than just splats for the false and true vals. For example, we can also do the transformation when FVal is an arbitrary fixed-width vector constant, i.e.

define <4 x i32> @select_reverse(<4 x i1> %a, <4 x i32> %b, <4 x i32> %c) {
  %a.rev = tail call <4 x i1> @llvm.experimental.vector.reverse.v4i1(<4 x i1> %a)
  %b.rev = tail call <4 x i32> @llvm.experimental.vector.reverse.v4i32(<4 x i32> %b)
  %select = select <4 x i1> %a.rev, <4 x i32> %b.rev, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
  ret <4 x i32> %select
}

[paulwalker-arm]

Fixed typo in comment and converted reverse_select_reverse to show flags get preserved.

[paulwalker-arm]

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

2340

I've updated reverse_select_reverse.

2350

The only situation where the combine can introduce more reversals than the original input IR is when all operands have more than one use. So if one or more operands have a single use then we can be sure the output will be the same or better.

For the case where the number of reversals is the same the hope is that at some point the reversals will bubble to a point where back-back reversals are seen with both then removed.

2354

vector.reverse is not typically used for fixed length vectors as such intrinsics should be converted to shufflevector instructions where the existing combines will kick in.

For scalable vectors is there an idiom outside of splats where the operand can be rewritten without introducing an explicit reversal?

[david-arm]

LGTM! C'est magnifique. :)

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/CmpInstAnalysis.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/OverflowInstAnalysis.h"
 #include "llvm/Analysis/ValueTracking.h"
+#include "llvm/Analysis/VectorUtils.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
static Instruction *foldSelectToCopysign(SelectInst &Sel,
   // not care about its sign.
   Value *MagArg = ConstantFP::get(SelType, abs(*TC));
   Function *F = Intrinsic::getDeclaration(Sel.getModule(), Intrinsic::copysign,
                                           Sel.getType());
   return CallInst::Create(F, { MagArg, X });
 }
 
 Instruction *InstCombinerImpl::foldVectorSelect(SelectInst &Sel) {
+  if (!isa<VectorType>(Sel.getType()))
+    return nullptr;
+
+  Value *Cond = Sel.getCondition();
+  Value *TVal = Sel.getTrueValue();
+  Value *FVal = Sel.getFalseValue();
+  Value *C, *X, *Y;
+
+  if (match(Cond, m_VecReverse(m_Value(C)))) {
+    auto createSelReverse = [&](Value *C, Value *X, Value *Y) {
+      Value *V = Builder.CreateSelect(C, X, Y, Sel.getName(), &Sel);
+      if (auto *I = dyn_cast<Instruction>(V))
+        I->copyIRFlags(&Sel);
+      Module *M = Sel.getModule();
+      Function *F = Intrinsic::getDeclaration(
+          M, Intrinsic::experimental_vector_reverse, V->getType());
+      return CallInst::Create(F, V);
+    };
+
+    if (match(TVal, m_VecReverse(m_Value(X)))) {
+      // select rev(C), rev(X), rev(Y) --> rev(select C, X, Y)
+      if (match(FVal, m_VecReverse(m_Value(Y))) &&
+          (Cond->hasOneUse() || TVal->hasOneUse() || FVal->hasOneUse()))
+        return createSelReverse(C, X, Y);
+
+      // select rev(C), rev(X), FValSplat --> rev(select C, X, FValSplat)
+      if ((Cond->hasOneUse() || TVal->hasOneUse()) && isSplatValue(FVal))
+        return createSelReverse(C, X, FVal);
+    }
+    // select rev(C), TValSplat, rev(Y) --> rev(select C, TValSplat, Y)
+    else if (isSplatValue(TVal) && match(FVal, m_VecReverse(m_Value(Y))) &&
+             (Cond->hasOneUse() || FVal->hasOneUse()))
+      return createSelReverse(C, TVal, Y);
+  }
+
   auto *VecTy = dyn_cast<FixedVectorType>(Sel.getType());
   if (!VecTy)
     return nullptr;
 
   unsigned NumElts = VecTy->getNumElements();
   APInt UndefElts(NumElts, 0);
   APInt AllOnesEltMask(APInt::getAllOnes(NumElts));
   if (Value *V = SimplifyDemandedVectorElts(&Sel, AllOnesEltMask, UndefElts)) {
     if (V != &Sel)
       return replaceInstUsesWith(Sel, V);
     return &Sel;
   }
 
   // A select of a "select shuffle" with a common operand can be rearranged
   // to select followed by "select shuffle". Because of poison, this only works
   // in the case of a shuffle with no undefined mask elements.
-  Value *Cond = Sel.getCondition();
-  Value *TVal = Sel.getTrueValue();
-  Value *FVal = Sel.getFalseValue();
-  Value *X, *Y;
   ArrayRef<int> Mask;
   if (match(TVal, m_OneUse(m_Shuffle(m_Value(X), m_Value(Y), m_Mask(Mask)))) &&
       !is_contained(Mask, UndefMaskElem) &&
       cast<ShuffleVectorInst>(TVal)->isSelect()) {
     if (X == FVal) {
       // select Cond, (shuf_sel X, Y), X --> shuf_sel X, (select Cond, Y, X)
       Value *NewSel = Builder.CreateSelect(Cond, Y, X, "sel", &Sel);
       return new ShuffleVectorInst(X, NewSel, Mask);

llvm/test/Transforms/InstCombine/vector-reverse.ll

;
   %b.splat = shufflevector <vscale x 4 x i32> %b.insert, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
   call void @use_nxv4i32(<vscale x 4 x i32> %a.rev)
   %cmp = icmp ult <vscale x 4 x i32> %b.splat, %a.rev
   ret <vscale x 4 x i1> %cmp
 }
 
 define <vscale x 4 x i32> @select_reverse(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, <vscale x 4 x i32> %c) {
 ; CHECK-LABEL: @select_reverse(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
-; CHECK-NEXT:    [[C_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[C:%.*]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x i32> [[B:%.*]], <vscale x 4 x i32> [[C:%.*]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %c)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.rev
   ret <vscale x 4 x i32> %select
 }
 
 ; %a.rev has multiple uses
 define <vscale x 4 x i32> @select_reverse_1(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, <vscale x 4 x i32> %c) {
 ; CHECK-LABEL: @select_reverse_1(
 ; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
-; CHECK-NEXT:    [[C_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[C:%.*]])
 ; CHECK-NEXT:    call void @use_nxv4i1(<vscale x 4 x i1> [[A_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A]], <vscale x 4 x i32> [[B:%.*]], <vscale x 4 x i32> [[C:%.*]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %c)
   call void @use_nxv4i1(<vscale x 4 x i1> %a.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.rev
   ret <vscale x 4 x i32> %select
 }
 
 ; %b.rev has multiple uses
 define <vscale x 4 x i32> @select_reverse_2(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, <vscale x 4 x i32> %c) {
 ; CHECK-LABEL: @select_reverse_2(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
 ; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
-; CHECK-NEXT:    [[C_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[C:%.*]])
 ; CHECK-NEXT:    call void @use_nxv4i32(<vscale x 4 x i32> [[B_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x i32> [[B]], <vscale x 4 x i32> [[C:%.*]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %c)
   call void @use_nxv4i32(<vscale x 4 x i32> %b.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.rev
   ret <vscale x 4 x i32> %select
 }
 
 ; %c.rev has multiple uses
 define <vscale x 4 x i32> @select_reverse_3(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, <vscale x 4 x i32> %c) {
 ; CHECK-LABEL: @select_reverse_3(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[C:%.*]])
 ; CHECK-NEXT:    call void @use_nxv4i32(<vscale x 4 x i32> [[C_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x i32> [[B:%.*]], <vscale x 4 x i32> [[C]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %c)
   call void @use_nxv4i32(<vscale x 4 x i32> %c.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.rev
   ret <vscale x 4 x i32> %select
 }
 
 ; %a.rev and %b.rev have multiple uses
 define <vscale x 4 x i32> @select_reverse_4(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, <vscale x 4 x i32> %c) {
 ; CHECK-LABEL: @select_reverse_4(
 ; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
 ; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
-; CHECK-NEXT:    [[C_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[C:%.*]])
 ; CHECK-NEXT:    call void @use_nxv4i1(<vscale x 4 x i1> [[A_REV]])
 ; CHECK-NEXT:    call void @use_nxv4i32(<vscale x 4 x i32> [[B_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A]], <vscale x 4 x i32> [[B]], <vscale x 4 x i32> [[C:%.*]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %c)
   call void @use_nxv4i1(<vscale x 4 x i1> %a.rev)
   call void @use_nxv4i32(<vscale x 4 x i32> %b.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.rev
   ret <vscale x 4 x i32> %select
 }
 
 ; %a.rev and %c.rev have multiple uses
 define <vscale x 4 x i32> @select_reverse_5(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, <vscale x 4 x i32> %c) {
 ; CHECK-LABEL: @select_reverse_5(
 ; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[C:%.*]])
 ; CHECK-NEXT:    call void @use_nxv4i1(<vscale x 4 x i1> [[A_REV]])
 ; CHECK-NEXT:    call void @use_nxv4i32(<vscale x 4 x i32> [[C_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A]], <vscale x 4 x i32> [[B:%.*]], <vscale x 4 x i32> [[C]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %c)
   call void @use_nxv4i1(<vscale x 4 x i1> %a.rev)
   call void @use_nxv4i32(<vscale x 4 x i32> %c.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.rev
   ret <vscale x 4 x i32> %select
 }
 
 ; %b.rev and %c.rev have multiple uses
 define <vscale x 4 x i32> @select_reverse_6(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, <vscale x 4 x i32> %c) {
 ; CHECK-LABEL: @select_reverse_6(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
 ; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[C:%.*]])
 ; CHECK-NEXT:    call void @use_nxv4i32(<vscale x 4 x i32> [[B_REV]])
 ; CHECK-NEXT:    call void @use_nxv4i32(<vscale x 4 x i32> [[C_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x i32> [[B]], <vscale x 4 x i32> [[C]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %c)
   call void @use_nxv4i32(<vscale x 4 x i32> %b.rev)
   call void @use_nxv4i32(<vscale x 4 x i32> %c.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.rev
;
   call void @use_nxv4i32(<vscale x 4 x i32> %b.rev)
   call void @use_nxv4i32(<vscale x 4 x i32> %c.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.rev
   ret <vscale x 4 x i32> %select
 }
 
 define <vscale x 4 x i32> @select_reverse_splat_false(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, i32 %c) {
 ; CHECK-LABEL: @select_reverse_splat_false(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_INSERT:%.*]] = insertelement <vscale x 4 x i32> poison, i32 [[C:%.*]], i64 0
 ; CHECK-NEXT:    [[C_SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[C_INSERT]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_SPLAT]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x i32> [[B:%.*]], <vscale x 4 x i32> [[C_SPLAT]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.insert = insertelement <vscale x 4 x i32> poison, i32 %c, i32 0
   %c.splat = shufflevector <vscale x 4 x i32> %c.insert, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.splat
   ret <vscale x 4 x i32> %select
 }
 
 ; %a.rev has multiple uses
 define <vscale x 4 x i32> @select_reverse_splat_false_1(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, i32 %c) {
 ; CHECK-LABEL: @select_reverse_splat_false_1(
 ; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_INSERT:%.*]] = insertelement <vscale x 4 x i32> poison, i32 [[C:%.*]], i64 0
 ; CHECK-NEXT:    [[C_SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[C_INSERT]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
 ; CHECK-NEXT:    call void @use_nxv4i1(<vscale x 4 x i1> [[A_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_SPLAT]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A]], <vscale x 4 x i32> [[B:%.*]], <vscale x 4 x i32> [[C_SPLAT]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.insert = insertelement <vscale x 4 x i32> poison, i32 %c, i32 0
   %c.splat = shufflevector <vscale x 4 x i32> %c.insert, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
   call void @use_nxv4i1(<vscale x 4 x i1> %a.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.splat
   ret <vscale x 4 x i32> %select
 }
 
 ; %b.rev has multiple uses
 define <vscale x 4 x i32> @select_reverse_splat_false_2(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, i32 %c) {
 ; CHECK-LABEL: @select_reverse_splat_false_2(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
 ; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_INSERT:%.*]] = insertelement <vscale x 4 x i32> poison, i32 [[C:%.*]], i64 0
 ; CHECK-NEXT:    [[C_SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[C_INSERT]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
 ; CHECK-NEXT:    call void @use_nxv4i32(<vscale x 4 x i32> [[B_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[B_REV]], <vscale x 4 x i32> [[C_SPLAT]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x i32> [[B]], <vscale x 4 x i32> [[C_SPLAT]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.insert = insertelement <vscale x 4 x i32> poison, i32 %c, i32 0
   %c.splat = shufflevector <vscale x 4 x i32> %c.insert, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
   call void @use_nxv4i32(<vscale x 4 x i32> %b.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.splat
;
   call void @use_nxv4i1(<vscale x 4 x i1> %a.rev)
   call void @use_nxv4i32(<vscale x 4 x i32> %b.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %b.rev, <vscale x 4 x i32> %c.splat
   ret <vscale x 4 x i32> %select
 }
 
 define <vscale x 4 x i32> @select_reverse_splat_true(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, i32 %c) {
 ; CHECK-LABEL: @select_reverse_splat_true(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_INSERT:%.*]] = insertelement <vscale x 4 x i32> poison, i32 [[C:%.*]], i64 0
 ; CHECK-NEXT:    [[C_SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[C_INSERT]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[C_SPLAT]], <vscale x 4 x i32> [[B_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x i32> [[C_SPLAT]], <vscale x 4 x i32> [[B:%.*]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.insert = insertelement <vscale x 4 x i32> poison, i32 %c, i32 0
   %c.splat = shufflevector <vscale x 4 x i32> %c.insert, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %c.splat, <vscale x 4 x i32> %b.rev
   ret <vscale x 4 x i32> %select
 }
 
 ; %a.rev has multiple uses
 define <vscale x 4 x i32> @select_reverse_splat_true_1(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, i32 %c) {
 ; CHECK-LABEL: @select_reverse_splat_true_1(
 ; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_INSERT:%.*]] = insertelement <vscale x 4 x i32> poison, i32 [[C:%.*]], i64 0
 ; CHECK-NEXT:    [[C_SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[C_INSERT]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
 ; CHECK-NEXT:    call void @use_nxv4i1(<vscale x 4 x i1> [[A_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[C_SPLAT]], <vscale x 4 x i32> [[B_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A]], <vscale x 4 x i32> [[C_SPLAT]], <vscale x 4 x i32> [[B:%.*]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.insert = insertelement <vscale x 4 x i32> poison, i32 %c, i32 0
   %c.splat = shufflevector <vscale x 4 x i32> %c.insert, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
   call void @use_nxv4i1(<vscale x 4 x i1> %a.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %c.splat, <vscale x 4 x i32> %b.rev
   ret <vscale x 4 x i32> %select
 }
 
 ; %b.rev has multiple uses
 define <vscale x 4 x i32> @select_reverse_splat_true_2(<vscale x 4 x i1> %a, <vscale x 4 x i32> %b, i32 %c) {
 ; CHECK-LABEL: @select_reverse_splat_true_2(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
 ; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[B:%.*]])
 ; CHECK-NEXT:    [[C_INSERT:%.*]] = insertelement <vscale x 4 x i32> poison, i32 [[C:%.*]], i64 0
 ; CHECK-NEXT:    [[C_SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[C_INSERT]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
 ; CHECK-NEXT:    call void @use_nxv4i32(<vscale x 4 x i32> [[B_REV]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x i32> [[C_SPLAT]], <vscale x 4 x i32> [[B_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x i32> [[C_SPLAT]], <vscale x 4 x i32> [[B]]
+; CHECK-NEXT:    [[SELECT:%.*]] = call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> [[SELECT1]])
 ; CHECK-NEXT:    ret <vscale x 4 x i32> [[SELECT]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %b)
   %c.insert = insertelement <vscale x 4 x i32> poison, i32 %c, i32 0
   %c.splat = shufflevector <vscale x 4 x i32> %c.insert, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
   call void @use_nxv4i32(<vscale x 4 x i32> %b.rev)
   %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x i32> %c.splat, <vscale x 4 x i32> %b.rev
;
   %b.rev = tail call <vscale x 4 x float> @llvm.experimental.vector.reverse.nxv4f32(<vscale x 4 x float> %b)
   %cmp = fcmp olt <vscale x 4 x float> %a.rev, %b.rev
   %cmp.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %cmp)
   ret <vscale x 4 x i1> %cmp.rev
 }
 
 define <vscale x 4 x float> @reverse_select_reverse(<vscale x 4 x i1> %a, <vscale x 4 x float> %b, <vscale x 4 x float> %c) {
 ; CHECK-LABEL: @reverse_select_reverse(
-; CHECK-NEXT:    [[A_REV:%.*]] = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> [[A:%.*]])
-; CHECK-NEXT:    [[B_REV:%.*]] = tail call <vscale x 4 x float> @llvm.experimental.vector.reverse.nxv4f32(<vscale x 4 x float> [[B:%.*]])
-; CHECK-NEXT:    [[C_REV:%.*]] = tail call <vscale x 4 x float> @llvm.experimental.vector.reverse.nxv4f32(<vscale x 4 x float> [[C:%.*]])
-; CHECK-NEXT:    [[SELECT:%.*]] = select <vscale x 4 x i1> [[A_REV]], <vscale x 4 x float> [[B_REV]], <vscale x 4 x float> [[C_REV]]
-; CHECK-NEXT:    [[SELECT_REV:%.*]] = tail call <vscale x 4 x float> @llvm.experimental.vector.reverse.nxv4f32(<vscale x 4 x float> [[SELECT]])
-; CHECK-NEXT:    ret <vscale x 4 x float> [[SELECT_REV]]
+; CHECK-NEXT:    [[SELECT1:%.*]] = select fast <vscale x 4 x i1> [[A:%.*]], <vscale x 4 x float> [[B:%.*]], <vscale x 4 x float> [[C:%.*]]
+; CHECK-NEXT:    ret <vscale x 4 x float> [[SELECT1]]
 ;
   %a.rev = tail call <vscale x 4 x i1> @llvm.experimental.vector.reverse.nxv4i1(<vscale x 4 x i1> %a)
   %b.rev = tail call <vscale x 4 x float> @llvm.experimental.vector.reverse.nxv4f32(<vscale x 4 x float> %b)
   %c.rev = tail call <vscale x 4 x float> @llvm.experimental.vector.reverse.nxv4f32(<vscale x 4 x float> %c)
-  %select = select <vscale x 4 x i1> %a.rev, <vscale x 4 x float> %b.rev, <vscale x 4 x float> %c.rev
+  %select = select fast <vscale x 4 x i1> %a.rev, <vscale x 4 x float> %b.rev, <vscale x 4 x float> %c.rev
   %select.rev = tail call <vscale x 4 x float> @llvm.experimental.vector.reverse.nxv4f32(<vscale x 4 x float> %select)
   ret <vscale x 4 x float> %select.rev
 }
 
 define <vscale x 4 x float> @reverse_unop_reverse(<vscale x 4 x float> %a) {
 ; CHECK-LABEL: @reverse_unop_reverse(
 ; CHECK-NEXT:    [[NEG1:%.*]] = fneg <vscale x 4 x float> [[A:%.*]]
 ; CHECK-NEXT:    ret <vscale x 4 x float> [[NEG1]]