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Revert "[InstCombine] sext(trunc(x)) --> sext(x) iff trunc is NSW (PR49543)"

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I forgot about the case where we sign-extend to width smaller than the original.

This reverts commit 1e6ca23ab8e350c7bab5d7f93e4d3dee18d180cc.
This commit is contained in:
Roman Lebedev 2021-04-21 01:10:10 +03:00
parent 3c5afdb7f4
commit 2608e4a8c5
2 changed files with 11 additions and 18 deletions
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18
lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -1493,22 +1493,12 @@ Instruction *InstCombinerImpl::visitSExt(SExtInst &CI) {
// If the input is a trunc from the destination type, then turn sext(trunc(x))
// into shifts.
Value *X;
if (match(Src, m_Trunc(m_Value(X)))) {
if (match(Src, m_OneUse(m_Trunc(m_Value(X)))) && X->getType() == DestTy) {
// sext(trunc(X)) --> ashr(shl(X, C), C)
unsigned SrcBitSize = SrcTy->getScalarSizeInBits();
unsigned DestBitSize = DestTy->getScalarSizeInBits();
unsigned XBitSize = X->getType()->getScalarSizeInBits();
// Iff X had more sign bits than the number of bits that were chopped off
// by the truncation, we can directly sign-extend the X.
unsigned XNumSignBits = ComputeNumSignBits(X, 0, &CI);
if (XNumSignBits > (XBitSize - SrcBitSize))
return CastInst::Create(Instruction::SExt, X, DestTy);
if (Src->hasOneUse() && X->getType() == DestTy) {
// sext(trunc(X)) --> ashr(shl(X, C), C)
Constant *ShAmt = ConstantInt::get(DestTy, DestBitSize - SrcBitSize);
return BinaryOperator::CreateAShr(Builder.CreateShl(X, ShAmt), ShAmt);
}
Constant *ShAmt = ConstantInt::get(DestTy, DestBitSize - SrcBitSize);
return BinaryOperator::CreateAShr(Builder.CreateShl(X, ShAmt), ShAmt);
}
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))

11
test/Transforms/InstCombine/sext-of-trunc-nsw.ll
View File

@ -13,7 +13,8 @@ define i16 @t0(i8 %x) {
; CHECK-LABEL: @t0(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 5
; CHECK-NEXT: call void @use8(i8 [[A]])
; CHECK-NEXT: [[C:%.*]] = sext i8 [[A]] to i16
; CHECK-NEXT: [[B:%.*]] = trunc i8 [[A]] to i4
; CHECK-NEXT: [[C:%.*]] = sext i4 [[B]] to i16
; CHECK-NEXT: ret i16 [[C]]
;
%a = ashr i8 %x, 5
@ -27,7 +28,8 @@ define i16 @t1(i8 %x) {
; CHECK-LABEL: @t1(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 4
; CHECK-NEXT: call void @use8(i8 [[A]])
; CHECK-NEXT: [[C:%.*]] = sext i8 [[A]] to i16
; CHECK-NEXT: [[B:%.*]] = trunc i8 [[A]] to i4
; CHECK-NEXT: [[C:%.*]] = sext i4 [[B]] to i16
; CHECK-NEXT: ret i16 [[C]]
;
%a = ashr i8 %x, 4
@ -57,7 +59,8 @@ define <2 x i16> @t3_vec(<2 x i8> %x) {
; CHECK-LABEL: @t3_vec(
; CHECK-NEXT: [[A:%.*]] = ashr <2 x i8> [[X:%.*]], <i8 4, i8 4>
; CHECK-NEXT: call void @usevec(<2 x i8> [[A]])
; CHECK-NEXT: [[C:%.*]] = sext <2 x i8> [[A]] to <2 x i16>
; CHECK-NEXT: [[B:%.*]] = trunc <2 x i8> [[A]] to <2 x i4>
; CHECK-NEXT: [[C:%.*]] = sext <2 x i4> [[B]] to <2 x i16>
; CHECK-NEXT: ret <2 x i16> [[C]]
;
%a = ashr <2 x i8> %x, <i8 4, i8 4>
@ -88,7 +91,7 @@ define i16 @t5_extrause(i8 %x) {
; CHECK-NEXT: call void @use8(i8 [[A]])
; CHECK-NEXT: [[B:%.*]] = trunc i8 [[A]] to i4
; CHECK-NEXT: call void @use4(i4 [[B]])
; CHECK-NEXT: [[C:%.*]] = sext i8 [[A]] to i16
; CHECK-NEXT: [[C:%.*]] = sext i4 [[B]] to i16
; CHECK-NEXT: ret i16 [[C]]
;
%a = ashr i8 %x, 5