[llvm] r340926 - [InstCombine] remove unnecessary shuffle undef folding

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Wed Aug 29 06:24:34 2018
New Revision: 340926

URL: http://llvm.org/viewvc/llvm-project?rev=340926&view=rev
Log:
[InstCombine] remove unnecessary shuffle undef folding

Add a test for constant folding to show that 
(shuffle undef, undef, mask)
should already be handled via instsimplify.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
    llvm/trunk/test/Analysis/ConstantFolding/vector-undef-elts.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp?rev=340926&r1=340925&r2=340926&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp Wed Aug 29 06:24:34 2018
@@ -1379,13 +1379,6 @@ Instruction *InstCombiner::visitShuffleV
   // Canonicalize shuffle(x    ,x,mask) -> shuffle(x, undef,mask')
   // Canonicalize shuffle(undef,x,mask) -> shuffle(x, undef,mask').
   if (LHS == RHS || isa<UndefValue>(LHS)) {
-    if (isa<UndefValue>(LHS) && LHS == RHS) {
-      // shuffle(undef,undef,mask) -> undef.
-      Value *Result = (VWidth == LHSWidth)
-                      ? LHS : UndefValue::get(SVI.getType());
-      return replaceInstUsesWith(SVI, Result);
-    }
-
     // Remap any references to RHS to use LHS.
     SmallVector<Constant*, 16> Elts;
     for (unsigned i = 0, e = LHSWidth; i != VWidth; ++i) {

Modified: llvm/trunk/test/Analysis/ConstantFolding/vector-undef-elts.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ConstantFolding/vector-undef-elts.ll?rev=340926&r1=340925&r2=340926&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ConstantFolding/vector-undef-elts.ll (original)
+++ llvm/trunk/test/Analysis/ConstantFolding/vector-undef-elts.ll Wed Aug 29 06:24:34 2018
@@ -59,3 +59,11 @@ define <3 x float> @fadd_commute() {
   ret <3 x float> %c
 }
 
+define <4 x i32> @shuffle_of_undefs(<4 x i32> %v1, <4 x i32> %v2) {
+; CHECK-LABEL: @shuffle_of_undefs(
+; CHECK-NEXT:    ret <4 x i32> undef
+;
+  %r = shufflevector <4 x i32> undef, <4 x i32> undef, <4 x i32> <i32 5, i32 1, i32 2, i32 3>
+  ret <4 x i32> %r
+}
+