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[DAGCombiner] Don't fold zext_vector_inreg/sext_vector_inreg(undef) to undef. Fold to 0.

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zext_vector_inreg needs to produces 0s in the extended bits and
sext_vector_inreg needs to produce upper bits that are all the
same. So we should fold them to a 0 vector instead of undef.

Fixes PR46585.
This commit is contained in:
Craig Topper
2020-07-04 11:42:00 -07:00
parent 21d8f66d20
commit 120c5f1057
2 changed files with 5 additions and 3 deletions
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6
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@@ -11086,8 +11086,9 @@ SDValue DAGCombiner::visitSIGN_EXTEND_VECTOR_INREG(SDNode *N) {
SDValue N0 = N->getOperand(0);
EVT VT = N->getValueType(0);
// sext_vector_inreg(undef) = 0 because the top bit will all be the same.
if (N0.isUndef())
return DAG.getUNDEF(VT);
return DAG.getConstant(0, SDLoc(N), VT);
if (SDValue Res = tryToFoldExtendOfConstant(N, TLI, DAG, LegalTypes))
return Res;
@@ -11102,8 +11103,9 @@ SDValue DAGCombiner::visitZERO_EXTEND_VECTOR_INREG(SDNode *N) {
SDValue N0 = N->getOperand(0);
EVT VT = N->getValueType(0);
// zext_vector_inreg(undef) = 0 because the top bits will be zero.
if (N0.isUndef())
return DAG.getUNDEF(VT);
return DAG.getConstant(0, SDLoc(N), VT);
if (SDValue Res = tryToFoldExtendOfConstant(N, TLI, DAG, LegalTypes))
return Res;

2
llvm/test/CodeGen/X86/pr46585.ll
View File

@@ -7,7 +7,7 @@
define void @spam() local_unnamed_addr {
; CHECK-LABEL: spam:
; CHECK: ## %bb.0: ## %bb
; CHECK-NEXT: pmovmskb %xmm0, %eax
; CHECK-NEXT: xorl %eax, %eax
; CHECK-NEXT: testb %al, %al
; CHECK-NEXT: je LBB0_2
; CHECK-NEXT: ## %bb.1: ## %bb9