[llvm] [SCCP] Strengthen two-instruction range checks (PR #162008)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Sun Oct 5 23:42:20 PDT 2025
https://github.com/dtcxzyw updated https://github.com/llvm/llvm-project/pull/162008
>From 6ef74bba5c5f79ddfdb770b90c5fa00f35443cfe Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sun, 5 Oct 2025 19:10:45 +0800
Subject: [PATCH 1/3] [SCCP] Add pre-commit tests. NFC.
---
.../Transforms/SCCP/relax-range-checks.ll | 24 +++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/llvm/test/Transforms/SCCP/relax-range-checks.ll b/llvm/test/Transforms/SCCP/relax-range-checks.ll
index 90722f350aa9e..420b11e00ba79 100644
--- a/llvm/test/Transforms/SCCP/relax-range-checks.ll
+++ b/llvm/test/Transforms/SCCP/relax-range-checks.ll
@@ -89,4 +89,28 @@ define i1 @relax_range_check_multiuse(i8 range(i8 0, 5) %x) {
ret i1 %ret
}
+define i1 @range_check_to_icmp_eq1(i32 range(i32 0, 4) %x) {
+; CHECK-LABEL: define i1 @range_check_to_icmp_eq1(
+; CHECK-SAME: i32 range(i32 0, 4) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i32 [[X]], -3
+; CHECK-NEXT: [[TMP1:%.*]] = icmp uge i32 [[X]], 3
+; CHECK-NEXT: ret i1 [[TMP1]]
+;
+ %off = add nsw i32 %x, -3
+ %cmp = icmp ult i32 %off, 2
+ ret i1 %cmp
+}
+
+define i1 @range_check_to_icmp_eq2(i32 range(i32 -1, 2) %x) {
+; CHECK-LABEL: define i1 @range_check_to_icmp_eq2(
+; CHECK-SAME: i32 range(i32 -1, 2) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i32 [[X]], -1
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[OFF]], -2
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add nsw i32 %x, -1
+ %cmp = icmp ult i32 %off, -2
+ ret i1 %cmp
+}
+
declare void @use(i8)
>From 75dcb6acf9acec248fb1b4c814aa8d9745edde22 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sun, 5 Oct 2025 19:24:38 +0800
Subject: [PATCH 2/3] [SCCP] Strengthen two-instruction range checks
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 39 +++++++++++--------
.../Transforms/SCCP/relax-range-checks.ll | 4 +-
2 files changed, 24 insertions(+), 19 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index af216cd9214bf..2e8e5ba18d933 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -317,24 +317,29 @@ static Value *simplifyInstruction(SCCPSolver &Solver,
// Early exit if we know nothing about X.
if (LRange.isFullSet())
return nullptr;
- // We are allowed to refine the comparison to either true or false for out
- // of range inputs. Here we refine the comparison to true, i.e. we relax
- // the range check.
- auto NewCR = CR->exactUnionWith(LRange.inverse());
- // TODO: Check if we can narrow the range check to an equality test.
- // E.g, for X in [0, 4), X - 3 u< 2 -> X == 3
- if (!NewCR)
+ auto ConvertCRToICmp =
+ [&](const std::optional<ConstantRange> &NewCR) -> Value * {
+ ICmpInst::Predicate Pred;
+ APInt RHS;
+ // Check if we can represent NewCR as an icmp predicate.
+ if (NewCR && NewCR->getEquivalentICmp(Pred, RHS)) {
+ IRBuilder<NoFolder> Builder(&Inst);
+ Value *NewICmp =
+ Builder.CreateICmp(Pred, X, ConstantInt::get(X->getType(), RHS));
+ InsertedValues.insert(NewICmp);
+ return NewICmp;
+ }
return nullptr;
- ICmpInst::Predicate Pred;
- APInt RHS;
- // Check if we can represent NewCR as an icmp predicate.
- if (NewCR->getEquivalentICmp(Pred, RHS)) {
- IRBuilder<NoFolder> Builder(&Inst);
- Value *NewICmp =
- Builder.CreateICmp(Pred, X, ConstantInt::get(X->getType(), RHS));
- InsertedValues.insert(NewICmp);
- return NewICmp;
- }
+ };
+ // We are allowed to refine the comparison to either true or false for out
+ // of range inputs.
+ // Here we refine the comparison to false, and check if we can narrow the
+ // range check to an equality test.
+ if (auto *V = ConvertCRToICmp(CR->exactIntersectWith(LRange)))
+ return V;
+ // Here we refine the comparison to true, i.e. we relax the range check.
+ if (auto *V = ConvertCRToICmp(CR->exactUnionWith(LRange.inverse())))
+ return V;
}
}
diff --git a/llvm/test/Transforms/SCCP/relax-range-checks.ll b/llvm/test/Transforms/SCCP/relax-range-checks.ll
index 420b11e00ba79..34e48136df37a 100644
--- a/llvm/test/Transforms/SCCP/relax-range-checks.ll
+++ b/llvm/test/Transforms/SCCP/relax-range-checks.ll
@@ -93,7 +93,7 @@ define i1 @range_check_to_icmp_eq1(i32 range(i32 0, 4) %x) {
; CHECK-LABEL: define i1 @range_check_to_icmp_eq1(
; CHECK-SAME: i32 range(i32 0, 4) [[X:%.*]]) {
; CHECK-NEXT: [[OFF:%.*]] = add nsw i32 [[X]], -3
-; CHECK-NEXT: [[TMP1:%.*]] = icmp uge i32 [[X]], 3
+; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[X]], 3
; CHECK-NEXT: ret i1 [[TMP1]]
;
%off = add nsw i32 %x, -3
@@ -105,7 +105,7 @@ define i1 @range_check_to_icmp_eq2(i32 range(i32 -1, 2) %x) {
; CHECK-LABEL: define i1 @range_check_to_icmp_eq2(
; CHECK-SAME: i32 range(i32 -1, 2) [[X:%.*]]) {
; CHECK-NEXT: [[OFF:%.*]] = add nsw i32 [[X]], -1
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[OFF]], -2
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%off = add nsw i32 %x, -1
>From 4b3b116cabe9f608524fd072209ff49828b29b24 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 6 Oct 2025 14:41:50 +0800
Subject: [PATCH 3/3] [SCCP] Adjust comments. NFC.
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 2e8e5ba18d933..9693ae6b8ceb5 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -334,7 +334,7 @@ static Value *simplifyInstruction(SCCPSolver &Solver,
// We are allowed to refine the comparison to either true or false for out
// of range inputs.
// Here we refine the comparison to false, and check if we can narrow the
- // range check to an equality test.
+ // range check to a simpler test.
if (auto *V = ConvertCRToICmp(CR->exactIntersectWith(LRange)))
return V;
// Here we refine the comparison to true, i.e. we relax the range check.
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