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[InstSimplify] fold rotate of zero to zero 

This is part of solving more general rotate patterns seen in
bugs related to:
https://llvm.org/PR51575

https://alive2.llvm.org/ce/z/fjKwqv
This commit is contained in:
Sanjay Patel 2021-08-22 09:10:52 -04:00
parent a0ebac4466
commit d41e308f10
2 changed files with 7 additions and 4 deletions
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5
llvm/lib/Analysis/InstructionSimplify.cpp
View File

@ -5855,6 +5855,11 @@ static Value *simplifyIntrinsic(CallBase *Call, const SimplifyQuery &Q) {
if (ShAmtC->urem(BitWidth).isNullValue())
return Call->getArgOperand(IID == Intrinsic::fshl ? 0 : 1);
}
// Rotating zero by anything is zero.
if (match(Op0, m_Zero()) && match(Op1, m_Zero()))
return ConstantInt::getNullValue(F->getReturnType());
return nullptr;
}
case Intrinsic::experimental_constrained_fma: {

6
llvm/test/Transforms/InstSimplify/call.ll
View File

@ -960,8 +960,7 @@ define i9 @fshr_ops_poison6() {
define i8 @fshl_zero(i8 %shamt) {
; CHECK-LABEL: @fshl_zero(
; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.fshl.i8(i8 0, i8 0, i8 [[SHAMT:%.*]])
; CHECK-NEXT: ret i8 [[R]]
; CHECK-NEXT: ret i8 0
;
%r = call i8 @llvm.fshl.i8(i8 0, i8 0, i8 %shamt)
ret i8 %r
@ -969,8 +968,7 @@ define i8 @fshl_zero(i8 %shamt) {
define <2 x i8> @fshr_zero_vec(<2 x i8> %shamt) {
; CHECK-LABEL: @fshr_zero_vec(
; CHECK-NEXT: [[R:%.*]] = call <2 x i8> @llvm.fshr.v2i8(<2 x i8> zeroinitializer, <2 x i8> <i8 0, i8 undef>, <2 x i8> [[SHAMT:%.*]])
; CHECK-NEXT: ret <2 x i8> [[R]]
; CHECK-NEXT: ret <2 x i8> zeroinitializer
;
%r = call <2 x i8> @llvm.fshr.v2i8(<2 x i8> zeroinitializer, <2 x i8> <i8 0, i8 undef>, <2 x i8> %shamt)
ret <2 x i8> %r