Skip to content

[InstCombine] Fold umax(X, C) + -C into usub.sat(X, C) #118195

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

Merged
merged 2 commits into from
Dec 1, 2024
Merged

[InstCombine] Fold umax(X, C) + -C into usub.sat(X, C) #118195

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
6e8cebe
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Dec 1, 2024
60d830e
[InstCombine] Fold `umax(X, C) + -C` into `usub.sat(X, C)`
dtcxzyw Dec 1, 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
6 changes: 6 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -994,6 +994,12 @@ Instruction *InstCombinerImpl::foldAddWithConstant(BinaryOperator &Add) {
}
}

// umax(X, C) + -C --> usub.sat(X, C)
if (match(Op0, m_OneUse(m_UMax(m_Value(X), m_SpecificInt(-*C)))))
return replaceInstUsesWith(
Add, Builder.CreateBinaryIntrinsic(
Intrinsic::usub_sat, X, ConstantInt::get(Add.getType(), -*C)));

// Fold (add (zext (add X, -1)), 1) -> (zext X) if X is non-zero.
// TODO: There's a general form for any constant on the outer add.
if (C->isOne()) {
Expand Down
36 changes: 36 additions & 0 deletions llvm/test/Transforms/InstCombine/saturating-add-sub.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2316,3 +2316,39 @@ define i32 @uadd_sat_via_add_swapped_cmp_select_nonstrict(i32 %x, i32 %y) {
%r = select i1 %c, i32 %a, i32 -1
ret i32 %r
}

define i8 @fold_add_umax_to_usub(i8 %a) {
; CHECK-LABEL: @fold_add_umax_to_usub(
; CHECK-NEXT: [[SEL:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[A:%.*]], i8 10)
; CHECK-NEXT: ret i8 [[SEL]]
;
%umax = call i8 @llvm.umax.i8(i8 %a, i8 10)
%sel = add i8 %umax, -10
ret i8 %sel
}

define i8 @fold_add_umax_to_usub_incorrect_rhs(i8 %a) {
; CHECK-LABEL: @fold_add_umax_to_usub_incorrect_rhs(
; CHECK-NEXT: [[UMAX:%.*]] = call i8 @llvm.umax.i8(i8 [[A:%.*]], i8 10)
; CHECK-NEXT: [[SEL:%.*]] = add i8 [[UMAX]], -11
; CHECK-NEXT: ret i8 [[SEL]]
;
%umax = call i8 @llvm.umax.i8(i8 %a, i8 10)
%sel = add i8 %umax, -11
ret i8 %sel
}

define i8 @fold_add_umax_to_usub_multiuse(i8 %a) {
; CHECK-LABEL: @fold_add_umax_to_usub_multiuse(
; CHECK-NEXT: [[UMAX:%.*]] = call i8 @llvm.umax.i8(i8 [[A:%.*]], i8 10)
; CHECK-NEXT: call void @usei8(i8 [[UMAX]])
; CHECK-NEXT: [[SEL:%.*]] = add i8 [[UMAX]], -10
; CHECK-NEXT: ret i8 [[SEL]]
;
%umax = call i8 @llvm.umax.i8(i8 %a, i8 10)
call void @usei8(i8 %umax)
%sel = add i8 %umax, -10
ret i8 %sel
}

declare void @usei8(i8)