[llvm] r357272 - [InstCombine] move shuffle canonicalizations before other transforms

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Fri Mar 29 09:49:38 2019
New Revision: 357272

URL: http://llvm.org/viewvc/llvm-project?rev=357272&view=rev
Log:
[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().

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp?rev=357272&r1=357271&r2=357272&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp Fri Mar 29 09:49:38 2019
@@ -1599,36 +1599,12 @@ Instruction *InstCombiner::visitShuffleV
           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::visitShuffleV
     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::visitShuffleV
   //                +-----------+-----------+-----------+-----------+
   // 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();