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[AggressiveInstCombine] Fix unsigned overflow 

Fix issue reported here: https://reviews.llvm.org/D108091#2950930
This commit is contained in:
Anton Afanasyev 2021-08-18 08:11:54 +03:00
parent 6724d82ee2
commit 803270c0c6
2 changed files with 22 additions and 3 deletions
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6
llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp
View File

@ -282,9 +282,9 @@ Type *TruncInstCombine::getBestTruncatedType() {
if (I->getOpcode() == Instruction::Shl) {
KnownBits KnownRHS = computeKnownBits(I->getOperand(1), DL);
const unsigned SrcBitWidth = KnownRHS.getBitWidth();
unsigned MinBitWidth =
KnownRHS.getMaxValue().uadd_sat(APInt(SrcBitWidth, 1)).getZExtValue();
MinBitWidth = std::min(MinBitWidth, SrcBitWidth);
unsigned MinBitWidth = KnownRHS.getMaxValue()
.uadd_sat(APInt(SrcBitWidth, 1))
.getLimitedValue(SrcBitWidth);
if (MinBitWidth >= OrigBitWidth)
return nullptr;
Itr.second.MinBitWidth = MinBitWidth;

19
llvm/test/Transforms/AggressiveInstCombine/trunc_shifts.ll
View File

@ -73,6 +73,25 @@ define i16 @shl_var_bounded_shift_amount(i8 %x, i8 %y) {
ret i16 %trunc
}
; Negative test (https://reviews.llvm.org/D108091#2950930)
define i32 @shl_check_no_overflow(i32 %call62, i16 %call63) {
; CHECK-LABEL: @shl_check_no_overflow(
; CHECK-NEXT: [[CONV64142:%.*]] = zext i32 [[CALL62:%.*]] to i64
; CHECK-NEXT: [[CONV65:%.*]] = sext i16 [[CALL63:%.*]] to i64
; CHECK-NEXT: [[SH_PROM66:%.*]] = and i64 [[CONV65]], 4294967295
; CHECK-NEXT: [[SHL67:%.*]] = shl i64 [[CONV64142]], [[SH_PROM66]]
; CHECK-NEXT: [[CONV68:%.*]] = trunc i64 [[SHL67]] to i32
; CHECK-NEXT: ret i32 [[CONV68]]
;
%conv64142 = zext i32 %call62 to i64
%conv65 = sext i16 %call63 to i64
%sh_prom66 = and i64 %conv65, 4294967295
%shl67 = shl i64 %conv64142, %sh_prom66
%conv68 = trunc i64 %shl67 to i32
ret i32 %conv68
}
define <2 x i16> @shl_vector(<2 x i8> %x) {
; CHECK-LABEL: @shl_vector(
; CHECK-NEXT: [[Z:%.*]] = zext <2 x i8> [[X:%.*]] to <2 x i16>