[InstCombine] move shuffle canonicalizations before other transforms

This may not be NFC, but I'm not sure how to expose any diffs in
tests. In theory, it should be slightly more efficient and possibly
more profitable to do the canonicalizations (which can increase the
undef elements in the mask) ahead of SimplifyDemandedVectorElts().

llvm-svn: 357272

1 files changed, 27 insertions, 30 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 6889cd9189c..cb5c22c69be 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -1599,36 +1599,12 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
           LHS, RHS, SVI.getMask(), SVI.getType(), SQ.getWithInstruction(&SVI)))
     return replaceInstUsesWith(SVI, V);
 
-  if (Instruction *I = foldSelectShuffle(SVI, Builder, DL))
-    return I;
-
-  if (Instruction *I = narrowVectorSelect(SVI, Builder))
-    return I;
-
+  // Canonicalize shuffle(x    ,x,mask) -> shuffle(x, undef,mask')
+  // Canonicalize shuffle(undef,x,mask) -> shuffle(x, undef,mask').
   unsigned VWidth = SVI.getType()->getVectorNumElements();
-  APInt UndefElts(VWidth, 0);
-  APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
-  if (Value *V = SimplifyDemandedVectorElts(&SVI, AllOnesEltMask, UndefElts)) {
-    if (V != &SVI)
-      return replaceInstUsesWith(SVI, V);
-    return &SVI;
-  }
-
-  if (Instruction *I = foldIdentityExtractShuffle(SVI))
-    return I;
-
-  // This transform has the potential to lose undef knowledge, so it is
-  // intentionally placed after SimplifyDemandedVectorElts().
-  if (Instruction *I = foldShuffleWithInsert(SVI))
-    return I;
-
+  unsigned LHSWidth = LHS->getType()->getVectorNumElements();
   SmallVector<int, 16> Mask = SVI.getShuffleMask();
   Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
-  unsigned LHSWidth = LHS->getType()->getVectorNumElements();
-  bool MadeChange = false;
-
-  // Canonicalize shuffle(x    ,x,mask) -> shuffle(x, undef,mask')
-  // Canonicalize shuffle(undef,x,mask) -> shuffle(x, undef,mask').
   if (LHS == RHS || isa<UndefValue>(LHS)) {
     // Remap any references to RHS to use LHS.
     SmallVector<Constant*, 16> Elts;
@@ -1650,11 +1626,31 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
     SVI.setOperand(0, SVI.getOperand(1));
     SVI.setOperand(1, UndefValue::get(RHS->getType()));
     SVI.setOperand(2, ConstantVector::get(Elts));
-    LHS = SVI.getOperand(0);
-    RHS = SVI.getOperand(1);
-    MadeChange = true;
+    return &SVI;
   }
 
+  if (Instruction *I = foldSelectShuffle(SVI, Builder, DL))
+    return I;
+
+  if (Instruction *I = narrowVectorSelect(SVI, Builder))
+    return I;
+
+  APInt UndefElts(VWidth, 0);
+  APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
+  if (Value *V = SimplifyDemandedVectorElts(&SVI, AllOnesEltMask, UndefElts)) {
+    if (V != &SVI)
+      return replaceInstUsesWith(SVI, V);
+    return &SVI;
+  }
+
+  if (Instruction *I = foldIdentityExtractShuffle(SVI))
+    return I;
+
+  // This transform has the potential to lose undef knowledge, so it is
+  // intentionally placed after SimplifyDemandedVectorElts().
+  if (Instruction *I = foldShuffleWithInsert(SVI))
+    return I;
+
   if (VWidth == LHSWidth) {
     // Analyze the shuffle, are the LHS or RHS and identity shuffles?
     bool isLHSID, isRHSID;
@@ -1699,6 +1695,7 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
   //                +-----------+-----------+-----------+-----------+
   // Index range [6,10):              ^-----------^ Needs an extra shuffle.
   // Target type i40:           ^--------------^ Won't work, bail.
+  bool MadeChange = false;
   if (isShuffleExtractingFromLHS(SVI, Mask)) {
     Value *V = LHS;
     unsigned MaskElems = Mask.size();