[llvm] [InstCombine] optimize unnecessary sext instruction with add + cmp (PR #152291)
Gaurav Dhingra via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 14 05:31:52 PDT 2025
https://github.com/gxyd updated https://github.com/llvm/llvm-project/pull/152291
>From 9248064baf7bb9bce0d214d7a6fe94bc207a15d2 Mon Sep 17 00:00:00 2001
From: Gaurav Dhingra <gauravdhingra.gxyd at gmail.com>
Date: Thu, 24 Jul 2025 10:28:48 +0530
Subject: [PATCH 1/5] [InstCombine][test] add test for sext+add+cmp instruction
---
.../Transforms/InstCombine/sext_for_add_cmp.ll | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
create mode 100644 llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll
diff --git a/llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll b/llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll
new file mode 100644
index 0000000000000..c89555422f65e
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll
@@ -0,0 +1,17 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+define i1 @sext_add_cmp_to_add_cmp(i16 noundef %x) {
+; CHECK-LABEL: define i1 @sext_add_cmp_to_add_cmp(
+; CHECK-SAME: i16 noundef [[X:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*:]]
+; CHECK-NEXT: [[CONV:%.*]] = sext i16 [[X]] to i128
+; CHECK-NEXT: [[ADD:%.*]] = add nsw i128 [[CONV]], 128
+; CHECK-NEXT: [[OR_COND_I:%.*]] = icmp ult i128 [[ADD]], 256
+; CHECK-NEXT: ret i1 [[OR_COND_I]]
+;
+entry:
+ %conv = sext i16 %x to i128
+ %add = add i128 %conv, 128
+ %or.cond.i = icmp ult i128 %add, 256
+ ret i1 %or.cond.i
+}
>From ddfe8f2fa903c6fe4d3fffa8d31c3fd6c0437a35 Mon Sep 17 00:00:00 2001
From: Gaurav Dhingra <gauravdhingra.gxyd at gmail.com>
Date: Wed, 6 Aug 2025 16:19:53 +0530
Subject: [PATCH 2/5] [InstCombine] remove unnecessary sext instruction for
add+cmp
---
.../InstCombine/InstCombineCompares.cpp | 34 +++++++++++++++++++
.../InstCombine/InstCombineInternal.h | 1 +
2 files changed, 35 insertions(+)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index cf94d28100488..ae329e9aaec4c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6381,6 +6381,36 @@ Instruction *InstCombinerImpl::foldICmpWithZextOrSext(ICmpInst &ICmp) {
return new ICmpInst(CmpInst::ICMP_SLT, X, Constant::getNullValue(SrcTy));
}
+Instruction *InstCombinerImpl::foldICmpWithSextAndAdd(ICmpInst &ICmp) {
+ Value *X;
+ ConstantInt *Y, *Z;
+ // Match the pattern: icmp ult (add (sext X), Y), Z
+ // where X is a value, Y and Z are integer constants
+ // icmp ult (add(sext(X), Y)), Z -> icmp ult (add(X, Y)), Z
+ if (match(&ICmp, m_SpecificICmp(CmpInst::ICMP_ULT,
+ m_Add(m_SExt(m_Value(X)), m_ConstantInt(Y)),
+ m_ConstantInt(Z)))) {
+ Type *XType = X->getType();
+ if (!XType->isIntegerTy())
+ return nullptr;
+
+ unsigned XBitWidth = XType->getIntegerBitWidth();
+ auto YValue = Y->getSExtValue();
+ auto ZValue = Z->getSExtValue();
+
+ auto MinValue = -(1LL << (XBitWidth - 1));
+ auto MaxValue = (1LL << (XBitWidth - 1)) - 1;
+
+ // // Check if Y and Z fit within X's type without wrapping
+ if (YValue < MinValue || YValue > MaxValue || ZValue < MinValue || ZValue > MaxValue)
+ return nullptr; // Cannot optimize if Y or Z would wrap in X's type
+
+ Value *NewAdd = Builder.CreateAdd(X, ConstantInt::get(XType, YValue));
+ return new ICmpInst(CmpInst::ICMP_ULT, NewAdd, ConstantInt::get(XType, ZValue));
+ }
+ return nullptr;
+}
+
/// Handle icmp (cast x), (cast or constant).
Instruction *InstCombinerImpl::foldICmpWithCastOp(ICmpInst &ICmp) {
// If any operand of ICmp is a inttoptr roundtrip cast then remove it as
@@ -7727,6 +7757,10 @@ Instruction *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
}
}
+ if (Instruction *Res = foldICmpWithSextAndAdd(I)) {
+ return Res;
+ }
+
// In case of a comparison with two select instructions having the same
// condition, check whether one of the resulting branches can be simplified.
// If so, just compare the other branch and select the appropriate result.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index c67e27e5b3e7c..ed652720f0dac 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -744,6 +744,7 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
const APInt &C);
Instruction *foldICmpTruncWithTruncOrExt(ICmpInst &Cmp,
const SimplifyQuery &Q);
+ Instruction *foldICmpWithSextAndAdd(ICmpInst &ICmp);
Instruction *foldICmpAndConstant(ICmpInst &Cmp, BinaryOperator *And,
const APInt &C);
Instruction *foldICmpXorConstant(ICmpInst &Cmp, BinaryOperator *Xor,
>From 22d5e23984d5e2b894e4452049370a6dba265b9a Mon Sep 17 00:00:00 2001
From: Gaurav Dhingra <gauravdhingra.gxyd at gmail.com>
Date: Wed, 6 Aug 2025 16:21:30 +0530
Subject: [PATCH 3/5] [InstCombine][test] update tests for sext instruction
optimization
---
llvm/test/Transforms/InstCombine/icmp-add.ll | 5 ++---
llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll | 5 ++---
2 files changed, 4 insertions(+), 6 deletions(-)
diff --git a/llvm/test/Transforms/InstCombine/icmp-add.ll b/llvm/test/Transforms/InstCombine/icmp-add.ll
index 1a41c1f3e1045..df85f5a3caa65 100644
--- a/llvm/test/Transforms/InstCombine/icmp-add.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-add.ll
@@ -3259,9 +3259,8 @@ define i1 @zext_range_check_mergable(i8 %x) {
define i1 @sext_range_check_ult(i8 %x) {
; CHECK-LABEL: @sext_range_check_ult(
; CHECK-NEXT: entry:
-; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[X:%.*]] to i32
-; CHECK-NEXT: [[ADD:%.*]] = add nsw i32 [[CONV]], -4
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[ADD]], 3
+; CHECK-NEXT: [[TMP0:%.*]] = add i8 [[X:%.*]], -4
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[TMP0]], 3
; CHECK-NEXT: ret i1 [[CMP]]
;
entry:
diff --git a/llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll b/llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll
index c89555422f65e..b8617df750abb 100644
--- a/llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll
+++ b/llvm/test/Transforms/InstCombine/sext_for_add_cmp.ll
@@ -4,9 +4,8 @@ define i1 @sext_add_cmp_to_add_cmp(i16 noundef %x) {
; CHECK-LABEL: define i1 @sext_add_cmp_to_add_cmp(
; CHECK-SAME: i16 noundef [[X:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
-; CHECK-NEXT: [[CONV:%.*]] = sext i16 [[X]] to i128
-; CHECK-NEXT: [[ADD:%.*]] = add nsw i128 [[CONV]], 128
-; CHECK-NEXT: [[OR_COND_I:%.*]] = icmp ult i128 [[ADD]], 256
+; CHECK-NEXT: [[TMP0:%.*]] = add i16 [[X]], 128
+; CHECK-NEXT: [[OR_COND_I:%.*]] = icmp ult i16 [[TMP0]], 256
; CHECK-NEXT: ret i1 [[OR_COND_I]]
;
entry:
>From 7d93fd6f9b574ac18369d774eb129249d2e775e7 Mon Sep 17 00:00:00 2001
From: Gaurav Dhingra <gauravdhingra.gxyd at gmail.com>
Date: Wed, 13 Aug 2025 17:00:57 +0530
Subject: [PATCH 4/5] [InstCombine] use general condition for optimization
---
.../InstCombine/InstCombineCompares.cpp | 66 +++++++++++++++----
1 file changed, 54 insertions(+), 12 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index ae329e9aaec4c..3bfa1a22ccd62 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6383,30 +6383,72 @@ Instruction *InstCombinerImpl::foldICmpWithZextOrSext(ICmpInst &ICmp) {
Instruction *InstCombinerImpl::foldICmpWithSextAndAdd(ICmpInst &ICmp) {
Value *X;
- ConstantInt *Y, *Z;
+ Value *Y, *Z;
// Match the pattern: icmp ult (add (sext X), Y), Z
// where X is a value, Y and Z are integer constants
// icmp ult (add(sext(X), Y)), Z -> icmp ult (add(X, Y)), Z
if (match(&ICmp, m_SpecificICmp(CmpInst::ICMP_ULT,
- m_Add(m_SExt(m_Value(X)), m_ConstantInt(Y)),
- m_ConstantInt(Z)))) {
+ m_Add(m_SExt(m_Value(X)), m_Value(Y)),
+ m_Value(Z)))) {
Type *XType = X->getType();
if (!XType->isIntegerTy())
return nullptr;
unsigned XBitWidth = XType->getIntegerBitWidth();
- auto YValue = Y->getSExtValue();
- auto ZValue = Z->getSExtValue();
+ auto ExtractValue = [&](Value *V, Type *TargetType, int64_t &OutValue) -> Value* {
+ if (auto *C = dyn_cast<ConstantInt>(V)) {
+ OutValue = C->getSExtValue();
+ return ConstantInt::get(TargetType, OutValue);
+ }
+ if (match(V, m_SExt(m_Value()))) {
+ Value *Src = cast<SExtInst>(V)->getOperand(0);
+ if (Src->getType() == TargetType)
+ return Src;
+ }
+ return nullptr;
+ };
- auto MinValue = -(1LL << (XBitWidth - 1));
- auto MaxValue = (1LL << (XBitWidth - 1)) - 1;
+ int64_t YValue, ZValue;
+ Value *NewY = ExtractValue(Y, XType, YValue);
+ Value *NewZ = ExtractValue(Z, XType, ZValue);
+ if (!NewY || !NewZ)
+ return nullptr;
- // // Check if Y and Z fit within X's type without wrapping
- if (YValue < MinValue || YValue > MaxValue || ZValue < MinValue || ZValue > MaxValue)
- return nullptr; // Cannot optimize if Y or Z would wrap in X's type
+ bool AreYZVariables = match(Y, m_SExt(m_Value())) && match(Z, m_SExt(m_Value()));
+ if (AreYZVariables) {
+ bool FoundCondition = false;
+ BasicBlock *BB = ICmp.getParent();
+ for (Instruction &I : *BB) {
+ if (auto *Assume = dyn_cast<IntrinsicInst>(&I)) {
+ if (Assume->getIntrinsicID() == Intrinsic::assume) {
+ Value *Cond = Assume->getOperand(0);
+ ConstantInt *C;
+ APInt MaxValue(Z->getType()->getIntegerBitWidth(), 1);
+ MaxValue <<= (XBitWidth - 1);
+ APInt Limit = MaxValue;
+ Limit += 1;
+ if (match(Cond, m_SpecificICmp(CmpInst::ICMP_ULT,
+ m_Sub(m_SExt(m_Value(Y)), m_SExt(m_Value(Z))), m_ConstantInt(C))) &&
+ C->getValue().ule(Limit)) {
+ FoundCondition = true;
+ if (Assume->use_empty()) {
+ eraseInstFromFunction(*Assume);
+ }
+ break;
+ }
+ }
+ }
+ }
+ if (!FoundCondition)
+ return nullptr;
+ } else {
+ auto MaxValue = (1LL << (XBitWidth - 1));
+ if (YValue - ZValue > MaxValue || YValue - ZValue < -MaxValue)
+ return nullptr;
+ }
- Value *NewAdd = Builder.CreateAdd(X, ConstantInt::get(XType, YValue));
- return new ICmpInst(CmpInst::ICMP_ULT, NewAdd, ConstantInt::get(XType, ZValue));
+ Value *NewAdd = Builder.CreateAdd(X, NewY);
+ return new ICmpInst(CmpInst::ICMP_ULT, NewAdd, NewZ);
}
return nullptr;
}
>From 7c6ec79fdc9a4025eba999ba0fe966062b3659de Mon Sep 17 00:00:00 2001
From: Gaurav Dhingra <gauravdhingra.gxyd at gmail.com>
Date: Thu, 14 Aug 2025 18:00:55 +0530
Subject: [PATCH 5/5] [formatting] use clang-format to fix formatting issue
---
.../Transforms/InstCombine/InstCombineCompares.cpp | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 3bfa1a22ccd62..55cea92ebd263 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6395,7 +6395,8 @@ Instruction *InstCombinerImpl::foldICmpWithSextAndAdd(ICmpInst &ICmp) {
return nullptr;
unsigned XBitWidth = XType->getIntegerBitWidth();
- auto ExtractValue = [&](Value *V, Type *TargetType, int64_t &OutValue) -> Value* {
+ auto ExtractValue = [&](Value *V, Type *TargetType,
+ int64_t &OutValue) -> Value * {
if (auto *C = dyn_cast<ConstantInt>(V)) {
OutValue = C->getSExtValue();
return ConstantInt::get(TargetType, OutValue);
@@ -6414,7 +6415,8 @@ Instruction *InstCombinerImpl::foldICmpWithSextAndAdd(ICmpInst &ICmp) {
if (!NewY || !NewZ)
return nullptr;
- bool AreYZVariables = match(Y, m_SExt(m_Value())) && match(Z, m_SExt(m_Value()));
+ bool AreYZVariables =
+ match(Y, m_SExt(m_Value())) && match(Z, m_SExt(m_Value()));
if (AreYZVariables) {
bool FoundCondition = false;
BasicBlock *BB = ICmp.getParent();
@@ -6427,9 +6429,11 @@ Instruction *InstCombinerImpl::foldICmpWithSextAndAdd(ICmpInst &ICmp) {
MaxValue <<= (XBitWidth - 1);
APInt Limit = MaxValue;
Limit += 1;
- if (match(Cond, m_SpecificICmp(CmpInst::ICMP_ULT,
- m_Sub(m_SExt(m_Value(Y)), m_SExt(m_Value(Z))), m_ConstantInt(C))) &&
- C->getValue().ule(Limit)) {
+ if (match(Cond, m_SpecificICmp(
+ CmpInst::ICMP_ULT,
+ m_Sub(m_SExt(m_Value(Y)), m_SExt(m_Value(Z))),
+ m_ConstantInt(C))) &&
+ C->getValue().ule(Limit)) {
FoundCondition = true;
if (Assume->use_empty()) {
eraseInstFromFunction(*Assume);
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