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[InstCombine] Simplifiy sdiv -X, X into X == INT_MIN ? 1 : -1 #71768

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Merged
merged 4 commits into from
Nov 15, 2023
Merged

[InstCombine] Simplifiy sdiv -X, X into X == INT_MIN ? 1 : -1 #71768

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203b618
[InstCombine] Simplifiy sdiv -X, X into X == INT_MIN ? 1 : -1
Z572 Nov 8, 2023
71b8239
fixup! [InstCombine] Simplifiy sdiv -X, X into X == INT_MIN ? 1 : -1
Z572 Nov 15, 2023
62855d1
fixup! fixup! [InstCombine] Simplifiy sdiv -X, X into X == INT_MIN ? …
Z572 Nov 15, 2023
03c0c9c
fixup! fixup! fixup! [InstCombine] Simplifiy sdiv -X, X into X == INT…
Z572 Nov 15, 2023
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7 changes: 7 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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Expand Up @@ -1544,6 +1544,13 @@ Instruction *InstCombinerImpl::visitSDiv(BinaryOperator &I) {
}
}

// -X / X --> X == INT_MIN ? 1 : -1
if (isKnownNegation(Op0, Op1)) {
APInt MinVal = APInt::getSignedMinValue(Ty->getScalarSizeInBits());
Value *Cond = Builder.CreateICmpEQ(Op0, ConstantInt::get(Ty, MinVal));
return SelectInst::Create(Cond, ConstantInt::get(Ty, 1),
ConstantInt::getAllOnesValue(Ty));
}
return nullptr;
}

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82 changes: 82 additions & 0 deletions llvm/test/Transforms/InstCombine/div.ll
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Expand Up @@ -1432,6 +1432,88 @@ define <2 x i8> @sdiv_sdiv_mul_nsw(<2 x i8> %x, <2 x i8> %y, <2 x i8> %z) {
ret <2 x i8> %r
}

define i32 @sdiv_sub1(i32 %arg) {
; CHECK-LABEL: @sdiv_sub1(
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[ARG:%.*]], -2147483648
; CHECK-NEXT: [[DIV:%.*]] = select i1 [[TMP1]], i32 1, i32 -1
; CHECK-NEXT: ret i32 [[DIV]]
;
%neg = sub i32 0, %arg
%div = sdiv i32 %neg, %arg
ret i32 %div
}

define i32 @sdiv_sub2(i32 %arg) {
; CHECK-LABEL: @sdiv_sub2(
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[ARG:%.*]], -2147483648
; CHECK-NEXT: [[DIV:%.*]] = select i1 [[TMP1]], i32 1, i32 -1
; CHECK-NEXT: ret i32 [[DIV]]
;
%neg = sub i32 0, %arg
%div = sdiv i32 %arg, %neg
ret i32 %div
}
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Please also add a multi-use test (extra use of %neg). As a div is removed, we want to allow the transform with multi-use.

Please also test the case (x - y) / (y - x), which is one of the special cases isKnownNegation() handles.


define i32 @sub_sdiv_multiuse(i32 %arg) {
; CHECK-LABEL: @sub_sdiv_multiuse(
; CHECK-NEXT: [[NEG:%.*]] = sub i32 0, [[ARG:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[ARG]], -2147483648
; CHECK-NEXT: [[DIV:%.*]] = select i1 [[TMP1]], i32 1, i32 -1
; CHECK-NEXT: call void @use(i32 [[NEG]])
; CHECK-NEXT: ret i32 [[DIV]]
;
%neg = sub i32 0, %arg
%div = sdiv i32 %arg, %neg
call void @use(i32 %neg)
ret i32 %div
}

define i32 @sdiv_sub_sub(i32 %x ,i32 %y) {
; CHECK-LABEL: @sdiv_sub_sub(
; CHECK-NEXT: [[S:%.*]] = sub i32 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[S]], -2147483648
; CHECK-NEXT: [[D:%.*]] = select i1 [[TMP1]], i32 1, i32 -1
; CHECK-NEXT: ret i32 [[D]]
;
%s = sub i32 %x, %y
%u = sub i32 %y, %x
%d = sdiv i32 %s, %u
ret i32 %d
}

define i32 @sdiv_mul_sub(i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_mul_sub(
; CHECK-NEXT: [[M:%.*]] = mul i32 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[M]], -2147483648
; CHECK-NEXT: [[R:%.*]] = select i1 [[TMP1]], i32 1, i32 -1
; CHECK-NEXT: ret i32 [[R]]
;
%m = mul i32 %y, %x
%d = sub i32 0, %m
%r = sdiv i32 %d, %m
ret i32 %r
}

define i32 @sdiv_mul_sub_nsw(i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_mul_sub_nsw(
; CHECK-NEXT: ret i32 -1
;
%m = mul i32 %y, %x
%n = sub nsw i32 0, %m
%d = sdiv i32 %m, %n
ret i32 %d
}

define i32 @sdiv_mul_nsw_sub_nsw(i32 %x, i32 %y) {
; CHECK-LABEL: @sdiv_mul_nsw_sub_nsw(
; CHECK-NEXT: ret i32 -1
;
%m = mul nsw i32 %y, %x
%n = sub nsw i32 0, %m
%d = sdiv i32 %m, %n
ret i32 %d
}

; exact propagates

define i8 @sdiv_sdiv_mul_nsw_exact_exact(i8 %x, i8 %y, i8 %z) {
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