Skip to content

[InstCombine] Fold sext(trunc nsw) and zext(trunc nuw) #88609

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 5 commits into
base: main
Choose a base branch
from
Open

[InstCombine] Fold sext(trunc nsw) and zext(trunc nuw) #88609

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
17d3737
pre-commit: add tests
YanWQ-monad Apr 13, 2024
42a0818
InstCombine: fold `sext(trunc nsw)` and `zext(trunc nuw)`
YanWQ-monad Apr 13, 2024
7707f11
test: add more tests
YanWQ-monad Apr 13, 2024
b3ed492
revise code
YanWQ-monad Apr 13, 2024
e004c57
remove unused fold
YanWQ-monad Apr 13, 2024
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
26 changes: 20 additions & 6 deletions llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1188,9 +1188,19 @@ Instruction *InstCombinerImpl::visitZExt(ZExtInst &Zext) {
if (auto *CSrc = dyn_cast<TruncInst>(Src)) { // A->B->C cast
// TODO: Subsume this into EvaluateInDifferentType.

Value *A = CSrc->getOperand(0);
// If trunc has nuw flag, then convert directly to final type.
if (CSrc->hasNoUnsignedWrap()) {
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

You can also handle nsw if the zext has nneg.

CastInst *I = CastInst::CreateIntegerCast(A, DestTy, /*isSigned=*/false);
if (auto *ZExt = dyn_cast<ZExtInst>(I))
ZExt->setNonNeg();
if (auto *Trunc = dyn_cast<TruncInst>(I))
Trunc->setHasNoUnsignedWrap(true);
return I;
}

// Get the sizes of the types involved. We know that the intermediate type
// will be smaller than A or C, but don't know the relation between A and C.
Value *A = CSrc->getOperand(0);
unsigned SrcSize = A->getType()->getScalarSizeInBits();
unsigned MidSize = CSrc->getType()->getScalarSizeInBits();
unsigned DstSize = DestTy->getScalarSizeInBits();
Expand Down Expand Up @@ -1461,11 +1471,14 @@ Instruction *InstCombinerImpl::visitSExt(SExtInst &Sext) {

Value *X;
if (match(Src, m_Trunc(m_Value(X)))) {
// If the input has more sign bits than bits truncated, then convert
// directly to final type.
unsigned XBitSize = X->getType()->getScalarSizeInBits();
if (ComputeNumSignBits(X, 0, &Sext) > XBitSize - SrcBitSize)
return CastInst::CreateIntegerCast(X, DestTy, /* isSigned */ true);
// If trunc has nsw flag, then convert directly to final type.
auto *CSrc = cast<TruncInst>(Src);
if (CSrc->hasNoSignedWrap()) {
CastInst *I = CastInst::CreateIntegerCast(X, DestTy, /*isSigned=*/true);
if (auto *Trunc = dyn_cast<TruncInst>(I))
Trunc->setHasNoSignedWrap(true);
return I;
}

// If input is a trunc from the destination type, then convert into shifts.
if (Src->hasOneUse() && X->getType() == DestTy) {
Expand All @@ -1478,6 +1491,7 @@ Instruction *InstCombinerImpl::visitSExt(SExtInst &Sext) {
// the logic shift to arithmetic shift and eliminate the cast to
// intermediate type:
// sext (trunc (lshr Y, C)) --> sext/trunc (ashr Y, C)
unsigned XBitSize = X->getType()->getScalarSizeInBits();
Value *Y;
if (Src->hasOneUse() &&
match(X, m_LShr(m_Value(Y),
Expand Down
50 changes: 50 additions & 0 deletions llvm/test/Transforms/InstCombine/sext.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -423,3 +423,53 @@ define i64 @smear_set_bit_different_dest_type_wider_dst(i32 %x) {
%s = sext i8 %a to i64
ret i64 %s
}

define i32 @sext_trunc_nsw(i16 %x) {
; CHECK-LABEL: @sext_trunc_nsw(
; CHECK-NEXT: [[E:%.*]] = sext i16 [[X:%.*]] to i32
; CHECK-NEXT: ret i32 [[E]]
;
%c = trunc nsw i16 %x to i8
%e = sext i8 %c to i32
ret i32 %e
}

define i16 @sext_trunc_nsw_2(i32 %x) {
; CHECK-LABEL: @sext_trunc_nsw_2(
; CHECK-NEXT: [[E:%.*]] = trunc nsw i32 [[X:%.*]] to i16
; CHECK-NEXT: ret i16 [[E]]
;
%c = trunc nsw i32 %x to i8
%e = sext i8 %c to i16
ret i16 %e
}

define i16 @sext_trunc_nsw_3(i16 %x) {
; CHECK-LABEL: @sext_trunc_nsw_3(
; CHECK-NEXT: ret i16 [[E:%.*]]
;
%c = trunc nsw i16 %x to i8
%e = sext i8 %c to i16
ret i16 %e
}

define <2 x i32> @sext_trunc_nsw_vec(<2 x i16> %x) {
; CHECK-LABEL: @sext_trunc_nsw_vec(
; CHECK-NEXT: [[E:%.*]] = sext <2 x i16> [[X:%.*]] to <2 x i32>
; CHECK-NEXT: ret <2 x i32> [[E]]
;
%c = trunc nsw <2 x i16> %x to <2 x i8>
%e = sext <2 x i8> %c to <2 x i32>
ret <2 x i32> %e
}

define i32 @sext_trunc(i16 %x) {
; CHECK-LABEL: @sext_trunc(
; CHECK-NEXT: [[C:%.*]] = trunc i16 [[X:%.*]] to i8
; CHECK-NEXT: [[E:%.*]] = sext i8 [[C]] to i32
; CHECK-NEXT: ret i32 [[E]]
;
%c = trunc i16 %x to i8
%e = sext i8 %c to i32
ret i32 %e
}
50 changes: 50 additions & 0 deletions llvm/test/Transforms/InstCombine/zext.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -867,3 +867,53 @@ entry:
%res = zext nneg i2 %x to i32
ret i32 %res
}

define i32 @zext_trunc_nuw(i16 %x) {
; CHECK-LABEL: @zext_trunc_nuw(
; CHECK-NEXT: [[E1:%.*]] = zext nneg i16 [[X:%.*]] to i32
; CHECK-NEXT: ret i32 [[E1]]
;
%c = trunc nuw i16 %x to i8
%e = zext i8 %c to i32
ret i32 %e
}

define i16 @zext_trunc_nuw_2(i32 %x) {
; CHECK-LABEL: @zext_trunc_nuw_2(
; CHECK-NEXT: [[E:%.*]] = trunc nuw i32 [[X:%.*]] to i16
; CHECK-NEXT: ret i16 [[E]]
;
%c = trunc nuw i32 %x to i8
%e = zext i8 %c to i16
ret i16 %e
}

define i16 @zext_trunc_nuw_3(i16 %x) {
; CHECK-LABEL: @zext_trunc_nuw_3(
; CHECK-NEXT: ret i16 [[E:%.*]]
;
%c = trunc nuw i16 %x to i8
%e = zext i8 %c to i16
ret i16 %e
}

define <2 x i32> @zext_trunc_nuw_vec(<2 x i16> %x) {
; CHECK-LABEL: @zext_trunc_nuw_vec(
; CHECK-NEXT: [[E1:%.*]] = zext nneg <2 x i16> [[X:%.*]] to <2 x i32>
; CHECK-NEXT: ret <2 x i32> [[E1]]
;
%c = trunc nuw <2 x i16> %x to <2 x i8>
%e = zext <2 x i8> %c to <2 x i32>
ret <2 x i32> %e
}

define i32 @zext_trunc(i16 %x) {
; CHECK-LABEL: @zext_trunc(
; CHECK-NEXT: [[E:%.*]] = and i16 [[X:%.*]], 255
; CHECK-NEXT: [[E1:%.*]] = zext nneg i16 [[E]] to i32
; CHECK-NEXT: ret i32 [[E1]]
;
%c = trunc i16 %x to i8
%e = zext i8 %c to i32
ret i32 %e
}