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[InstCombine] foldSelectFunnelShift - block poison in funnel shift value 

As raised by @nlopes on D90382 - if this is not a rotate then the select was blocking poison from the 'shift-by-zero' non-TVal, but a funnel shift won't - so freeze it.
This commit is contained in:
Simon Pilgrim 2020-11-08 12:58:14 +00:00
parent 9fd7710497
commit 0fe91ad463
2 changed files with 15 additions and 3 deletions
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9
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -2374,6 +2374,15 @@ static Instruction *foldSelectFunnelShift(SelectInst &Sel,
Pred != ICmpInst::ICMP_EQ)
return nullptr;
// If this is not a rotate then the select was blocking poison from the
// 'shift-by-zero' non-TVal, but a funnel shift won't - so freeze it.
if (SV0 != SV1) {
if (IsFshl && !llvm::isGuaranteedNotToBePoison(SV1))
SV1 = Builder.CreateFreeze(SV1);
else if (!IsFshl && !llvm::isGuaranteedNotToBePoison(SV0))
SV0 = Builder.CreateFreeze(SV0);
}
// This is a funnel/rotate that avoids shift-by-bitwidth UB in a suboptimal way.
// Convert to funnel shift intrinsic.
Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;

9
llvm/test/Transforms/InstCombine/funnel.ll
View File

@ -285,7 +285,8 @@ define i8 @fshr_commute_8bit(i32 %x, i32 %y, i32 %shift) {
define i8 @fshr_select(i8 %x, i8 %y, i8 %shamt) {
; CHECK-LABEL: @fshr_select(
; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.fshr.i8(i8 [[X:%.*]], i8 [[Y:%.*]], i8 [[SHAMT:%.*]])
; CHECK-NEXT: [[TMP1:%.*]] = freeze i8 [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = call i8 @llvm.fshr.i8(i8 [[TMP1]], i8 [[Y:%.*]], i8 [[SHAMT:%.*]])
; CHECK-NEXT: ret i8 [[R]]
;
%cmp = icmp eq i8 %shamt, 0
@ -301,7 +302,8 @@ define i8 @fshr_select(i8 %x, i8 %y, i8 %shamt) {
define i16 @fshl_select(i16 %x, i16 %y, i16 %shamt) {
; CHECK-LABEL: @fshl_select(
; CHECK-NEXT: [[R:%.*]] = call i16 @llvm.fshl.i16(i16 [[X:%.*]], i16 [[Y:%.*]], i16 [[SHAMT:%.*]])
; CHECK-NEXT: [[TMP1:%.*]] = freeze i16 [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = call i16 @llvm.fshl.i16(i16 [[X:%.*]], i16 [[TMP1]], i16 [[SHAMT:%.*]])
; CHECK-NEXT: ret i16 [[R]]
;
%cmp = icmp eq i16 %shamt, 0
@ -317,7 +319,8 @@ define i16 @fshl_select(i16 %x, i16 %y, i16 %shamt) {
define <2 x i64> @fshl_select_vector(<2 x i64> %x, <2 x i64> %y, <2 x i64> %shamt) {
; CHECK-LABEL: @fshl_select_vector(
; CHECK-NEXT: [[R:%.*]] = call <2 x i64> @llvm.fshl.v2i64(<2 x i64> [[Y:%.*]], <2 x i64> [[X:%.*]], <2 x i64> [[SHAMT:%.*]])
; CHECK-NEXT: [[TMP1:%.*]] = freeze <2 x i64> [[X:%.*]]
; CHECK-NEXT: [[R:%.*]] = call <2 x i64> @llvm.fshl.v2i64(<2 x i64> [[Y:%.*]], <2 x i64> [[TMP1]], <2 x i64> [[SHAMT:%.*]])
; CHECK-NEXT: ret <2 x i64> [[R]]
;
%cmp = icmp eq <2 x i64> %shamt, zeroinitializer