Skip to content

[InstCombine] Propagate flags when folding consecutative shifts #94872

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

Closed
wants to merge 2 commits into from
Closed

[InstCombine] Propagate flags when folding consecutative shifts #94872

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
2ba7b74
[InstCombine] Add tests for propagating flags when folding consecutat…
goldsteinn Jun 8, 2024
ca70abe
[InstCombine] Propagate flags when folding consecutative shifts
goldsteinn Jun 8, 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
15 changes: 12 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -767,11 +767,20 @@ Instruction *InstCombinerImpl::FoldShiftByConstant(Value *Op0, Constant *C1,
// (C2 >> X) >> C1 --> (C2 >> C1) >> X
Constant *C2;
Value *X;
if (match(Op0, m_BinOp(I.getOpcode(), m_ImmConstant(C2), m_Value(X))))
return BinaryOperator::Create(
bool IsLeftShift = I.getOpcode() == Instruction::Shl;
if (match(Op0, m_BinOp(I.getOpcode(), m_ImmConstant(C2), m_Value(X)))) {
Instruction *R = BinaryOperator::Create(
I.getOpcode(), Builder.CreateBinOp(I.getOpcode(), C2, C1), X);
BinaryOperator *BO0 = cast<BinaryOperator>(Op0);
if (IsLeftShift) {
R->setHasNoUnsignedWrap(I.hasNoUnsignedWrap() &&
BO0->hasNoUnsignedWrap());
R->setHasNoSignedWrap(I.hasNoSignedWrap() && BO0->hasNoSignedWrap());
} else
R->setIsExact(I.isExact() && BO0->isExact());
return R;
}

bool IsLeftShift = I.getOpcode() == Instruction::Shl;
Type *Ty = I.getType();
unsigned TypeBits = Ty->getScalarSizeInBits();

Expand Down
80 changes: 80 additions & 0 deletions llvm/test/Transforms/InstCombine/shift.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2240,4 +2240,84 @@ define i129 @shift_zext_not_nneg(i8 %arg) {
ret i129 %shl
}

define i8 @src_shl_nsw(i8 %x) {
; CHECK-LABEL: @src_shl_nsw(
; CHECK-NEXT: [[R:%.*]] = shl nsw i8 32, [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%sh = shl nsw i8 1, %x
%r = shl nsw i8 %sh, 5
ret i8 %r
}

define i8 @src_shl_nsw_fail(i8 %x) {
; CHECK-LABEL: @src_shl_nsw_fail(
; CHECK-NEXT: [[R:%.*]] = shl i8 32, [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%sh = shl nsw i8 1, %x
%r = shl i8 %sh, 5
ret i8 %r
}

define i8 @src_shl_nuw(i8 %x) {
; CHECK-LABEL: @src_shl_nuw(
; CHECK-NEXT: [[R:%.*]] = shl nuw i8 12, [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%sh = shl nuw i8 3, %x
%r = shl nuw i8 %sh, 2
ret i8 %r
}

define i8 @src_shl_nuw_fail(i8 %x) {
; CHECK-LABEL: @src_shl_nuw_fail(
; CHECK-NEXT: [[R:%.*]] = shl i8 12, [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%sh = shl i8 3, %x
%r = shl nuw i8 %sh, 2
ret i8 %r
}

define i8 @src_lshr_exact(i8 %x) {
; CHECK-LABEL: @src_lshr_exact(
; CHECK-NEXT: [[R:%.*]] = lshr exact i8 48, [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%sh = lshr exact i8 96, %x
%r = lshr exact i8 %sh, 1
ret i8 %r
}

define i8 @src_lshr_exact_fail(i8 %x) {
; CHECK-LABEL: @src_lshr_exact_fail(
; CHECK-NEXT: [[R:%.*]] = lshr i8 48, [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%sh = lshr exact i8 96, %x
%r = lshr i8 %sh, 1
ret i8 %r
}

define i8 @src_ashr_exact(i8 %x) {
; CHECK-LABEL: @src_ashr_exact(
; CHECK-NEXT: [[R:%.*]] = lshr exact i8 8, [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%sh = ashr exact i8 32, %x
Copy link
Member

Choose a reason for hiding this comment

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

Can you replace LHS with a negative number?

%r = ashr exact i8 %sh, 2
ret i8 %r
}

define i8 @src_ashr_exact_fail(i8 %x) {
; CHECK-LABEL: @src_ashr_exact_fail(
; CHECK-NEXT: [[R:%.*]] = lshr i8 8, [[X:%.*]]
; CHECK-NEXT: ret i8 [[R]]
;
%sh = ashr i8 32, %x
%r = ashr exact i8 %sh, 2
ret i8 %r
}

declare i16 @llvm.umax.i16(i16, i16)
Loading