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[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.

llvm-svn: 340926
This commit is contained in:
Sanjay Patel 2018-08-29 13:24:34 +00:00
parent f6db5bcd38
commit 7a05641fa8
2 changed files with 8 additions and 7 deletions
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7
llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
View File

@ -1379,13 +1379,6 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
// 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) {

8
llvm/test/Analysis/ConstantFolding/vector-undef-elts.ll
View File

@ -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
}