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[SCCP] Simplify [us]cmp(X, Y) into X - Y (#144717)

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If the difference between [us]cmp's operands is not greater than 1, we
can simplify it into `X - Y`.
Alive2: https://alive2.llvm.org/ce/z/JS55so
llvm-opt-benchmark diff:
https://github.com/dtcxzyw/llvm-opt-benchmark/pull/2464/files
This commit is contained in:
Yingwei Zheng
2025-07-20 15:01:44 +08:00
committed by GitHub
parent 51af47e53c
commit 9e587ce6f0
2 changed files with 220 additions and 1 deletions
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36
llvm/lib/Transforms/Utils/SCCPSolver.cpp
View File

@@ -19,7 +19,9 @@
#include "llvm/Analysis/ValueLattice.h"
#include "llvm/Analysis/ValueLatticeUtils.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/NoFolder.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
@@ -245,11 +247,43 @@ static Value *simplifyInstruction(SCCPSolver &Solver,
const APInt *RHSC;
// Remove masking operations.
if (match(&Inst, m_And(m_Value(X), m_LowBitMask(RHSC)))) {
ConstantRange LRange = GetRange(Inst.getOperand(0));
ConstantRange LRange = GetRange(X);
if (LRange.getUnsignedMax().ule(*RHSC))
return X;
}
// Check if we can simplify [us]cmp(X, Y) to X - Y.
if (auto *Cmp = dyn_cast<CmpIntrinsic>(&Inst)) {
Value *LHS = Cmp->getOperand(0);
Value *RHS = Cmp->getOperand(1);
unsigned BitWidth = LHS->getType()->getScalarSizeInBits();
// Bail out on 1-bit comparisons.
if (BitWidth == 1)
return nullptr;
ConstantRange LRange = GetRange(LHS);
if (LRange.isSizeLargerThan(3))
return nullptr;
ConstantRange RRange = GetRange(RHS);
if (RRange.isSizeLargerThan(3))
return nullptr;
ConstantRange RHSLower = RRange.sub(APInt(BitWidth, 1));
ConstantRange RHSUpper = RRange.add(APInt(BitWidth, 1));
ICmpInst::Predicate Pred =
Cmp->isSigned() ? CmpInst::ICMP_SLE : CmpInst::ICMP_ULE;
if (!RHSLower.icmp(Pred, LRange) || !LRange.icmp(Pred, RHSUpper))
return nullptr;
IRBuilder<NoFolder> Builder(&Inst);
Value *Sub = Builder.CreateSub(LHS, RHS, Inst.getName(), /*HasNUW=*/false,
/*HasNSW=*/Cmp->isSigned());
InsertedValues.insert(Sub);
if (Sub->getType() != Inst.getType()) {
Sub = Builder.CreateSExtOrTrunc(Sub, Inst.getType());
InsertedValues.insert(Sub);
}
return Sub;
}
return nullptr;
}

185
llvm/test/Transforms/SCCP/uscmp.ll Normal file
View File

@@ -0,0 +1,185 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -passes=sccp -S < %s | FileCheck %s
define i32 @scmp_to_sub(i32 range(i32 -1, 2) %a) {
; CHECK-LABEL: define i32 @scmp_to_sub(
; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = sub nsw i32 [[A]], 0
; CHECK-NEXT: ret i32 [[SCMP]]
;
%scmp = call i32 @llvm.scmp(i32 %a, i32 0)
ret i32 %scmp
}
define i32 @scmp_zext_to_sub(i1 %a, i1 %b) {
; CHECK-LABEL: define i32 @scmp_zext_to_sub(
; CHECK-SAME: i1 [[A:%.*]], i1 [[B:%.*]]) {
; CHECK-NEXT: [[ZEXT_A:%.*]] = zext i1 [[A]] to i32
; CHECK-NEXT: [[ZEXT_B:%.*]] = zext i1 [[B]] to i32
; CHECK-NEXT: [[SCMP:%.*]] = sub nsw i32 [[ZEXT_A]], [[ZEXT_B]]
; CHECK-NEXT: ret i32 [[SCMP]]
;
%zext_a = zext i1 %a to i32
%zext_b = zext i1 %b to i32
%scmp = call i32 @llvm.scmp(i32 %zext_a, i32 %zext_b)
ret i32 %scmp
}
define i8 @scmp_to_sub_trunc(i32 range(i32 -1, 2) %a) {
; CHECK-LABEL: define i8 @scmp_to_sub_trunc(
; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
; CHECK-NEXT: [[SCMP1:%.*]] = sub nsw i32 [[A]], 0
; CHECK-NEXT: [[SCMP:%.*]] = trunc i32 [[SCMP1]] to i8
; CHECK-NEXT: ret i8 [[SCMP]]
;
%scmp = call i8 @llvm.scmp(i32 %a, i32 0)
ret i8 %scmp
}
define i64 @scmp_to_sub_sext(i32 range(i32 -1, 2) %a) {
; CHECK-LABEL: define i64 @scmp_to_sub_sext(
; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
; CHECK-NEXT: [[SCMP1:%.*]] = sub nsw i32 [[A]], 0
; CHECK-NEXT: [[SCMP:%.*]] = sext i32 [[SCMP1]] to i64
; CHECK-NEXT: ret i64 [[SCMP]]
;
%scmp = call i64 @llvm.scmp(i32 %a, i32 0)
ret i64 %scmp
}
define i32 @scmp_to_sub_small_range(i32 range(i32 -1, 1) %a) {
; CHECK-LABEL: define i32 @scmp_to_sub_small_range(
; CHECK-SAME: i32 range(i32 -1, 1) [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = sub nsw i32 [[A]], 0
; CHECK-NEXT: ret i32 [[SCMP]]
;
%scmp = call i32 @llvm.scmp(i32 %a, i32 0)
ret i32 %scmp
}
define i32 @ucmp_to_sub(i32 range(i32 0, 3) %a) {
; CHECK-LABEL: define i32 @ucmp_to_sub(
; CHECK-SAME: i32 range(i32 0, 3) [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = sub i32 [[A]], 1
; CHECK-NEXT: ret i32 [[SCMP]]
;
%ucmp = call i32 @llvm.ucmp(i32 %a, i32 1)
ret i32 %ucmp
}
define i8 @ucmp_to_sub_trunc(i32 range(i32 0, 3) %a) {
; CHECK-LABEL: define i8 @ucmp_to_sub_trunc(
; CHECK-SAME: i32 range(i32 0, 3) [[A:%.*]]) {
; CHECK-NEXT: [[UCMP1:%.*]] = sub i32 [[A]], 1
; CHECK-NEXT: [[UCMP:%.*]] = trunc i32 [[UCMP1]] to i8
; CHECK-NEXT: ret i8 [[UCMP]]
;
%ucmp = call i8 @llvm.ucmp(i32 %a, i32 1)
ret i8 %ucmp
}
define i64 @ucmp_to_sub_sext(i32 range(i32 0, 3) %a) {
; CHECK-LABEL: define i64 @ucmp_to_sub_sext(
; CHECK-SAME: i32 range(i32 0, 3) [[A:%.*]]) {
; CHECK-NEXT: [[UCMP1:%.*]] = sub i32 [[A]], 1
; CHECK-NEXT: [[UCMP:%.*]] = sext i32 [[UCMP1]] to i64
; CHECK-NEXT: ret i64 [[UCMP]]
;
%ucmp = call i64 @llvm.ucmp(i32 %a, i32 1)
ret i64 %ucmp
}
; TODO: we can fold this into %a.
define i32 @ucmp_to_sub_small_range(i32 range(i32 0, 2) %a) {
; CHECK-LABEL: define i32 @ucmp_to_sub_small_range(
; CHECK-SAME: i32 range(i32 0, 2) [[A:%.*]]) {
; CHECK-NEXT: [[UCMP:%.*]] = call i32 @llvm.ucmp.i32.i32(i32 [[A]], i32 0)
; CHECK-NEXT: ret i32 [[UCMP]]
;
%ucmp = call i32 @llvm.ucmp(i32 %a, i32 0)
ret i32 %ucmp
}
define i32 @scmp_to_sub_large_range(i32 range(i32 -1, 3) %a) {
; CHECK-LABEL: define i32 @scmp_to_sub_large_range(
; CHECK-SAME: i32 range(i32 -1, 3) [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 0)
; CHECK-NEXT: ret i32 [[SCMP]]
;
%scmp = call i32 @llvm.scmp(i32 %a, i32 0)
ret i32 %scmp
}
define i32 @ucmp_to_sub_large_range(i32 range(i32 -1, 3) %a) {
; CHECK-LABEL: define i32 @ucmp_to_sub_large_range(
; CHECK-SAME: i32 range(i32 -1, 3) [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.ucmp.i32.i32(i32 [[A]], i32 0)
; CHECK-NEXT: ret i32 [[SCMP]]
;
%ucmp = call i32 @llvm.ucmp(i32 %a, i32 0)
ret i32 %ucmp
}
define i32 @scmp_to_sub_wrap(i8 range(i8 127, -126) %a) {
; CHECK-LABEL: define i32 @scmp_to_sub_wrap(
; CHECK-SAME: i8 range(i8 127, -126) [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i8(i8 [[A]], i8 -128)
; CHECK-NEXT: ret i32 [[SCMP]]
;
%scmp = call i32 @llvm.scmp(i8 %a, i8 -128)
ret i32 %scmp
}
define i32 @ucmp_to_sub_wrap(i8 range(i8 -1, 2) %a) {
; CHECK-LABEL: define i32 @ucmp_to_sub_wrap(
; CHECK-SAME: i8 range(i8 -1, 2) [[A:%.*]]) {
; CHECK-NEXT: [[UCMP:%.*]] = call i32 @llvm.ucmp.i32.i8(i8 [[A]], i8 0)
; CHECK-NEXT: ret i32 [[UCMP]]
;
%ucmp = call i32 @llvm.ucmp(i8 %a, i8 0)
ret i32 %ucmp
}
; It is incorrect to convert a ucmp into sub when the input type is i1.
define i32 @ucmp_to_sub_i1_rhs_const(i1 %a) {
; CHECK-LABEL: define i32 @ucmp_to_sub_i1_rhs_const(
; CHECK-SAME: i1 [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.ucmp.i32.i1(i1 [[A]], i1 false)
; CHECK-NEXT: ret i32 [[SCMP]]
;
%ucmp = call i32 @llvm.ucmp(i1 %a, i1 false)
ret i32 %ucmp
}
; It is incorrect to convert a ucmp into sub when the input type is i1.
define i32 @ucmp_to_sub_i1_lhs_const(i1 %a) {
; CHECK-LABEL: define i32 @ucmp_to_sub_i1_lhs_const(
; CHECK-SAME: i1 [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.ucmp.i32.i1(i1 false, i1 [[A]])
; CHECK-NEXT: ret i32 [[SCMP]]
;
%ucmp = call i32 @llvm.ucmp(i1 false, i1 %a)
ret i32 %ucmp
}
; It is incorrect to convert a ucmp into sub when the input type is i1.
define i32 @ucmp_to_sub_i1(i1 %a, i1 %b) {
; CHECK-LABEL: define i32 @ucmp_to_sub_i1(
; CHECK-SAME: i1 [[A:%.*]], i1 [[B:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.ucmp.i32.i1(i1 [[A]], i1 [[B]])
; CHECK-NEXT: ret i32 [[SCMP]]
;
%ucmp = call i32 @llvm.ucmp(i1 %a, i1 %b)
ret i32 %ucmp
}
; It is incorrect to convert a scmp into sub when the input type is i1.
define i32 @scmp_to_sub_i1_rhs_const(i1 %a) {
; CHECK-LABEL: define i32 @scmp_to_sub_i1_rhs_const(
; CHECK-SAME: i1 [[A:%.*]]) {
; CHECK-NEXT: [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i1(i1 [[A]], i1 false)
; CHECK-NEXT: ret i32 [[SCMP]]
;
%scmp = call i32 @llvm.scmp(i1 %a, i1 false)
ret i32 %scmp
}