Skip to content

[InstCombine] Fold X - Y + Y * C -> X + Y * (C - 1) #117722

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
AZero13 wants to merge 2 commits into from
Closed

[InstCombine] Fold X - Y + Y * C -> X + Y * (C - 1) #117722

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
e7bc7db
[InstCombine] Pre-commit tests (NFC)
AZero13 Nov 26, 2024
05e8ccc
[InstCombine] Fold X - Y + Y * C -> X + Y * (C - 1)
AZero13 Nov 26, 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
14 changes: 14 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 @@ -1614,6 +1614,20 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
}
}

{
// A - B + B * C -> A + B * (C - 1)
const APInt *C;
if (((match(LHS, m_Sub(m_Value(A), m_Value(B))) &&
match(RHS, m_Mul(m_Specific(B), m_APInt(C)))) ||
(match(RHS, m_Sub(m_Value(A), m_Value(B))) &&
match(LHS, m_Mul(m_Specific(B), m_APInt(C))))) &&
LHS->hasOneUse() && RHS->hasOneUse()) {
Value *Mul =
Builder.CreateMul(B, ConstantInt::get(RHS->getType(), *C - 1));
return BinaryOperator::CreateAdd(A, Mul);
}
}

// X % C0 + (( X / C0 ) % C1) * C0 => X % (C0 * C1)
if (Value *V = SimplifyAddWithRemainder(I)) return replaceInstUsesWith(I, V);

Expand Down
104 changes: 104 additions & 0 deletions llvm/test/Transforms/InstCombine/addsub-constant-folding.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -750,3 +750,107 @@ define i8 @sub_from_constant_extra_use(i8 %x, i8 %y) {
%r = add i8 %sub, %y
ret i8 %r
}

define i32 @sub_plus_mul(i32 %x, i32 %y) {
; CHECK-LABEL: @sub_plus_mul(
; CHECK-NEXT: [[B:%.*]] = mul i32 [[Y:%.*]], 9
; CHECK-NEXT: [[C:%.*]] = add i32 [[A:%.*]], [[B]]
; CHECK-NEXT: ret i32 [[C]]
;
%a = sub i32 %x, %y
%b = mul i32 %y, 10
%c = add i32 %a, %b
ret i32 %c
}

define i32 @sub_plus_mul_2(i32 %x, i32 %y) {
; CHECK-LABEL: @sub_plus_mul_2(
; CHECK-NEXT: [[B:%.*]] = mul i32 [[Y:%.*]], -11
; CHECK-NEXT: [[C:%.*]] = add i32 [[A:%.*]], [[B]]
; CHECK-NEXT: ret i32 [[C]]
;
%a = sub i32 %x, %y
%b = mul i32 %y, -10
%c = add i32 %a, %b
ret i32 %c
}

define i32 @sub_plus_mul3(i32 %x, i32 %y) {
; CHECK-LABEL: @sub_plus_mul3(
; CHECK-NEXT: [[A:%.*]] = mul i32 [[Y:%.*]], 9
; CHECK-NEXT: [[C:%.*]] = add i32 [[B:%.*]], [[A]]
; CHECK-NEXT: ret i32 [[C]]
;
%a = mul i32 %y, 10
%b = sub i32 %x, %y
%c = add i32 %b, %a
ret i32 %c
}

define i32 @sub_plus_mul4(i32 %x, i32 %y) {
; CHECK-LABEL: @sub_plus_mul4(
; CHECK-NEXT: [[A:%.*]] = mul i32 [[Y:%.*]], -11
; CHECK-NEXT: [[C:%.*]] = add i32 [[B:%.*]], [[A]]
; CHECK-NEXT: ret i32 [[C]]
;
%a = mul i32 %y, -10
%b = sub i32 %x, %y
%c = add i32 %b, %a
ret i32 %c
}

define <2 x i8> @sub_plus_mul_splat(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @sub_plus_mul_splat(
; CHECK-NEXT: [[B:%.*]] = mul <2 x i8> [[Y:%.*]], splat (i8 6)
; CHECK-NEXT: [[C:%.*]] = add <2 x i8> [[A:%.*]], [[B]]
; CHECK-NEXT: ret <2 x i8> [[C]]
;
%a = sub <2 x i8> %x, %y
%b = mul <2 x i8> %y, splat(i8 7)
%c = add <2 x i8> %a, %b
ret <2 x i8> %c
}

;; <- Negative Tests ->

;; mul does not work if it is a power of 2, because it results in worse codegen
define i32 @neg_sub_plus_mul_pow2(i32 %x, i32 %y) {
; CHECK-LABEL: @neg_sub_plus_mul_pow2(
; CHECK-NEXT: [[A:%.*]] = sub i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[B:%.*]] = shl i32 [[Y]], 3
; CHECK-NEXT: [[C:%.*]] = add i32 [[A]], [[B]]
; CHECK-NEXT: ret i32 [[C]]
;
%a = sub i32 %x, %y
%b = mul i32 %y, 8
%c = add i32 %a, %b
ret i32 %c
}

define <2 x i8> @neg_sub_plus_mul_splat_shl(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @neg_sub_plus_mul_splat_shl(
; CHECK-NEXT: [[A:%.*]] = sub <2 x i8> [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[B:%.*]] = shl <2 x i8> [[Y]], splat (i8 3)
; CHECK-NEXT: [[C:%.*]] = add <2 x i8> [[A]], [[B]]
; CHECK-NEXT: ret <2 x i8> [[C]]
;
%a = sub <2 x i8> %x, %y
%b = mul <2 x i8> %y, splat(i8 8)
%c = add <2 x i8> %a, %b
ret <2 x i8> %c
}

define i32 @neg_sub_plus_mul_multiuse(i32 %x, i32 %y) {
; CHECK-LABEL: @neg_sub_plus_mul_multiuse(
; CHECK-NEXT: [[A:%.*]] = sub i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[B:%.*]] = mul i32 [[Y]], 7
; CHECK-NEXT: call void @use(i32 [[B]])
; CHECK-NEXT: [[C:%.*]] = add i32 [[A]], [[B]]
; CHECK-NEXT: ret i32 [[C]]
;
%a = sub i32 %x, %y
%b = mul i32 %y, 7
call void @use(i32 %b)
%c = add i32 %a, %b
ret i32 %c
}