[llvm] [InstCombine] Simplify fractions when there is no overflow (PR #92949)
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Tue May 21 16:22:29 PDT 2024
https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/92949
>From 2f7dc2c6e0e766be23c7df4e641253cb04979b23 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Tue, 21 May 2024 14:09:05 -0400
Subject: [PATCH] [InstCombine] Simplify fractions when there is no overlap
https://alive2.llvm.org/ce/z/-36zkQ
---
.../InstCombine/InstCombineMulDivRem.cpp | 76 ++++++++++++++++---
llvm/test/Transforms/InstCombine/div.ll | 15 +++-
2 files changed, 80 insertions(+), 11 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index ca1b1921404d8..ec178204ff105 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1057,7 +1057,8 @@ static Value *foldIDivShl(BinaryOperator &I, InstCombiner::BuilderTy &Builder) {
// (X * Y) s/ (X << Z) --> Y s/ (1 << Z)
if (IsSigned && HasNSW && (Op0->hasOneUse() || Op1->hasOneUse())) {
- Value *Shl = Builder.CreateShl(ConstantInt::get(Ty, 1), Z);
+ Value *Shl = Builder.CreateShl(ConstantInt::get(Ty, 1), Z, "", true,
+ HasNUW && HasNSW);
return Builder.CreateSDiv(Y, Shl, "", I.isExact());
}
}
@@ -1169,13 +1170,53 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
// (X * C1) / C2 -> X * (C1 / C2) if C1 is a multiple of C2.
if (isMultiple(*C1, *C2, Quotient, IsSigned)) {
- auto *Mul = BinaryOperator::Create(Instruction::Mul, X,
- ConstantInt::get(Ty, Quotient));
+ assert(!C1->isOne() && !C2->isOne() && !C1->isZero() && !C2->isZero() &&
+ "InstSimplify should have removed constants of 1!");
+ auto *Mul =
+ BinaryOperator::CreateNSWMul(X, ConstantInt::get(Ty, Quotient));
auto *OBO = cast<OverflowingBinaryOperator>(Op0);
- Mul->setHasNoUnsignedWrap(!IsSigned && OBO->hasNoUnsignedWrap());
- Mul->setHasNoSignedWrap(OBO->hasNoSignedWrap());
+ Mul->setHasNoUnsignedWrap(OBO->hasNoUnsignedWrap());
return Mul;
}
+
+ // We can reduce expressions of things like * 150 / 100 to * 3 / 2
+ if (Op0->hasOneUse() && !C2->isZero() &&
+ !(IsSigned && C1->isMinSignedValue() && C2->isAllOnes())) {
+ assert(!C2->isMinSignedValue() &&
+ "This should have been folded away by InstSimplify");
+ APInt GCD = APIntOps::GreatestCommonDivisor(C1->abs(), C2->abs());
+ if (!GCD.isOne() && !GCD.isZero()) {
+ APInt NewC1;
+ APInt NewC2;
+ if (IsSigned && C1->isNegative() && C2->isNegative()) {
+ NewC1 = C1->abs().udiv(GCD);
+ NewC2 = C2->abs().udiv(GCD);
+ } else if (IsSigned) {
+ NewC1 = C1->sdiv(GCD);
+ NewC2 = C2->sdiv(GCD);
+ } else {
+ NewC1 = C1->udiv(GCD);
+ NewC2 = C2->udiv(GCD);
+ }
+
+ auto *NewMul = Builder.CreateMul(
+ X, ConstantInt::get(Ty, NewC1), "",
+ /*NUW*/ cast<OverflowingBinaryOperator>(Op0)->hasNoUnsignedWrap(),
+ /*NSW*/ true);
+
+ if (IsSigned) {
+ auto *NewDiv =
+ BinaryOperator::CreateSDiv(NewMul, ConstantInt::get(Ty, NewC2));
+ NewDiv->setIsExact(I.isExact());
+ return NewDiv;
+ }
+
+ auto *NewDiv =
+ BinaryOperator::CreateUDiv(NewMul, ConstantInt::get(Ty, NewC2));
+ NewDiv->setIsExact(I.isExact());
+ return NewDiv;
+ }
+ }
}
if ((IsSigned && match(Op0, m_NSWShl(m_Value(X), m_APInt(C1))) &&
@@ -1198,8 +1239,8 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
auto *Mul = BinaryOperator::Create(Instruction::Mul, X,
ConstantInt::get(Ty, Quotient));
auto *OBO = cast<OverflowingBinaryOperator>(Op0);
- Mul->setHasNoUnsignedWrap(!IsSigned && OBO->hasNoUnsignedWrap());
- Mul->setHasNoSignedWrap(OBO->hasNoSignedWrap());
+ Mul->setHasNoUnsignedWrap(OBO->hasNoUnsignedWrap());
+ Mul->setHasNoSignedWrap(!IsSigned || OBO->hasNoSignedWrap());
return Mul;
}
}
@@ -1273,13 +1314,30 @@ Instruction *InstCombinerImpl::commonIDivTransforms(BinaryOperator &I) {
}
// (X << Z) / (X * Y) -> (1 << Z) / Y
- // TODO: Handle sdiv.
if (!IsSigned && Op1->hasOneUse() &&
match(Op0, m_NUWShl(m_Value(X), m_Value(Z))) &&
match(Op1, m_c_Mul(m_Specific(X), m_Value(Y))))
if (cast<OverflowingBinaryOperator>(Op1)->hasNoUnsignedWrap()) {
Instruction *NewDiv = BinaryOperator::CreateUDiv(
- Builder.CreateShl(ConstantInt::get(Ty, 1), Z, "", /*NUW*/ true), Y);
+ Builder.CreateShl(
+ ConstantInt::get(Ty, 1), Z, "", /*NUW*/ true,
+ cast<OverflowingBinaryOperator>(Op1)->hasNoSignedWrap()),
+ Y);
+ NewDiv->setIsExact(I.isExact());
+ return NewDiv;
+ }
+
+ // (X << Z) / (X * Y) -> (1 << Z) / Y
+ if (IsSigned && Op1->hasOneUse() &&
+ match(Op0, m_NSWShl(m_Value(X), m_Value(Z))) &&
+ match(Op1, m_c_Mul(m_Specific(X), m_Value(Y))))
+ if (cast<OverflowingBinaryOperator>(Op1)->hasNoSignedWrap()) {
+ Instruction *NewDiv = BinaryOperator::CreateSDiv(
+ Builder.CreateShl(
+ ConstantInt::get(Ty, 1), Z, "",
+ /*NUW*/ cast<OverflowingBinaryOperator>(Op1)->hasNoUnsignedWrap(),
+ /*NSW*/ true),
+ Y);
NewDiv->setIsExact(I.isExact());
return NewDiv;
}
diff --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index e8a25ff44d029..6f7e10aef515a 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -380,7 +380,7 @@ define i32 @test26(i32 %a) {
define i32 @test27(i32 %a) {
; CHECK-LABEL: @test27(
-; CHECK-NEXT: [[DIV:%.*]] = shl nuw i32 [[A:%.*]], 1
+; CHECK-NEXT: [[DIV:%.*]] = shl nuw nsw i32 [[A:%.*]], 1
; CHECK-NEXT: ret i32 [[DIV]]
;
%shl = shl nuw i32 %a, 2
@@ -390,7 +390,7 @@ define i32 @test27(i32 %a) {
define i32 @test28(i32 %a) {
; CHECK-LABEL: @test28(
-; CHECK-NEXT: [[DIV:%.*]] = mul nuw i32 [[A:%.*]], 12
+; CHECK-NEXT: [[DIV:%.*]] = mul nuw nsw i32 [[A:%.*]], 12
; CHECK-NEXT: ret i32 [[DIV]]
;
%mul = mul nuw i32 %a, 36
@@ -1678,6 +1678,17 @@ define i32 @sdiv_sdiv_mul_nsw_exact_use(i32 %x, i32 %y, i32 %z) {
ret i32 %r
}
+define i32 @x_times_150_over_100(i32 %x) {
+; CHECK-LABEL: @x_times_150_over_100(
+; CHECK-NEXT: [[TMP1:%.*]] = mul nuw nsw i32 [[X:%.*]], 3
+; CHECK-NEXT: [[D1:%.*]] = lshr i32 [[TMP1]], 1
+; CHECK-NEXT: ret i32 [[D1]]
+;
+ %m = mul nuw nsw i32 %x, 150
+ %d = udiv i32 %m, 100
+ ret i32 %d
+}
+
; negative test - must have nsw
define i8 @sdiv_sdiv_mul_nuw(i8 %x, i8 %y, i8 %z) {
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