[llvm] r301764 - InstructionSimplify: Simplify a shuffle with a undef mask to undef

[Zvi Rackover via llvm-commits]

Author: zvi
Date: Sun Apr 30 01:06:26 2017
New Revision: 301764

URL: http://llvm.org/viewvc/llvm-project?rev=301764&view=rev
Log:
InstructionSimplify: Simplify a shuffle with a undef mask to undef

Summary:
Following the discussion in pr32486, adding the simplification:
 shuffle %x, %y, undef -> undef

Reviewers: spatel, RKSimon, andreadb, davide

Reviewed By: spatel

Subscribers: jroelofs, davide, llvm-commits

Differential Revision: https://reviews.llvm.org/D32293

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/shufflevector.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=301764&r1=301763&r2=301764&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Sun Apr 30 01:06:26 2017
@@ -4049,6 +4049,9 @@ static Value *foldIdentityShuffles(int D
 static Value *SimplifyShuffleVectorInst(Value *Op0, Value *Op1, Constant *Mask,
                                         Type *RetTy, const SimplifyQuery &Q,
                                         unsigned MaxRecurse) {
+  if (isa<UndefValue>(Mask))
+    return UndefValue::get(RetTy);
+
   Type *InVecTy = Op0->getType();
   unsigned MaskNumElts = Mask->getType()->getVectorNumElements();
   unsigned InVecNumElts = InVecTy->getVectorNumElements();

Modified: llvm/trunk/test/Transforms/InstSimplify/shufflevector.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/shufflevector.ll?rev=301764&r1=301763&r2=301764&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/shufflevector.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/shufflevector.ll Sun Apr 30 01:06:26 2017
@@ -118,6 +118,14 @@ define <4 x i32> @undef_mask(<4 x i32> %
   ret <4 x i32> %shuf
 }
 
+define <4 x i32> @undef_mask_1(<4 x i32> %x, <4 x i32> %y) {
+; CHECK-LABEL: @undef_mask_1(
+; CHECK-NEXT:    ret <4 x i32> undef
+;
+  %shuf = shufflevector <4 x i32> %x, <4 x i32> %y, <4 x i32> undef
+  ret <4 x i32> %shuf
+}
+
 define <4 x i32> @identity_mask_0(<4 x i32> %x) {
 ; CHECK-LABEL: @identity_mask_0(
 ; CHECK-NEXT:    ret <4 x i32> [[X:%.*]]