[llvm] [SCCP] Relax 2-insts range check to one-icmp check (PR #187997)
Kunqiu Chen via llvm-commits
llvm-commits at lists.llvm.org
Fri May 1 02:14:59 PDT 2026
https://github.com/Camsyn updated https://github.com/llvm/llvm-project/pull/187997
>From 4b2a73fd025d96914d9358b30e86688a023885b2 Mon Sep 17 00:00:00 2001
From: Camsyn <camsyn at foxmail.com>
Date: Mon, 23 Mar 2026 17:47:30 +0800
Subject: [PATCH 1/8] Pre-commit tests
---
.../Transforms/SCCP/relax-range-checks.ll | 123 ++++++++++++++++++
1 file changed, 123 insertions(+)
diff --git a/llvm/test/Transforms/SCCP/relax-range-checks.ll b/llvm/test/Transforms/SCCP/relax-range-checks.ll
index 34e48136df37a..f7c4f6f468929 100644
--- a/llvm/test/Transforms/SCCP/relax-range-checks.ll
+++ b/llvm/test/Transforms/SCCP/relax-range-checks.ll
@@ -113,4 +113,127 @@ define i1 @range_check_to_icmp_eq2(i32 range(i32 -1, 2) %x) {
ret i1 %cmp
}
+define i1 @range_check_to_icmp_ult(i8 range(i8 2, 10) %x) {
+; CHECK-LABEL: define i1 @range_check_to_icmp_ult(
+; CHECK-SAME: i8 range(i8 2, 10) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], -2
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 4
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add i8 %x, -2
+ %cmp = icmp ult i8 %off, 4
+ ret i1 %cmp
+}
+
+define i1 @range_check_to_icmp_uge(i8 range(i8 2, 6) %x) {
+; CHECK-LABEL: define i1 @range_check_to_icmp_uge(
+; CHECK-SAME: i8 range(i8 2, 6) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], -4
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 2
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add nsw i8 %x, -4
+ %cmp = icmp ult i8 %off, 2
+ ret i1 %cmp
+}
+
+define i1 @range_check_to_icmp_slt(i8 range(i8 -56, 20) %x) {
+; CHECK-LABEL: define i1 @range_check_to_icmp_slt(
+; CHECK-SAME: i8 range(i8 -56, 20) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], 56
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 50
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add nsw i8 %x, 56
+ %cmp = icmp ult i8 %off, 50
+ ret i1 %cmp
+}
+
+define i1 @range_check_to_icmp_sge(i8 range(i8 -56, 20) %x) {
+; CHECK-LABEL: define i1 @range_check_to_icmp_sge(
+; CHECK-SAME: i8 range(i8 -56, 20) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], 16
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 36
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add nsw i8 %x, 16
+ %cmp = icmp ult i8 %off, 36
+ ret i1 %cmp
+}
+
+; Cover the early exit when ActiveCmpCR is already a one-icmp check.
+
+define i1 @range_check_intersection_to_icmp_eq(i32 range(i32 0, 4) %x) {
+; CHECK-LABEL: define i1 @range_check_intersection_to_icmp_eq(
+; CHECK-SAME: i32 range(i32 0, 4) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i32 [[X]], -3
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X]], 3
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add nsw i32 %x, -3
+ %cmp = icmp ult i32 %off, 2
+ ret i1 %cmp
+}
+
+define i1 @range_check_intersection_to_icmp_ult(i8 range(i8 0, 10) %x) {
+; CHECK-LABEL: define i1 @range_check_intersection_to_icmp_ult(
+; CHECK-SAME: i8 range(i8 0, 10) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nuw nsw i8 [[X]], 2
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[X]], 4
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add i8 %x, 2
+ %cmp = icmp ult i8 %off, 6
+ ret i1 %cmp
+}
+
+define i1 @range_check_intersection_to_icmp_slt(i8 range(i8 -128, -100) %x) {
+; CHECK-LABEL: define i1 @range_check_intersection_to_icmp_slt(
+; CHECK-SAME: i8 range(i8 -128, -100) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add i8 [[X]], -120
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X]], -118
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add i8 %x, -120
+ %cmp = icmp ult i8 %off, 18
+ ret i1 %cmp
+}
+
+define i1 @range_check_intersection_to_icmp_uge(i8 range(i8 -6, 0) %x) {
+; CHECK-LABEL: define i1 @range_check_intersection_to_icmp_uge(
+; CHECK-SAME: i8 range(i8 -6, 0) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], 2
+; CHECK-NEXT: [[CMP:%.*]] = icmp uge i8 [[X]], -2
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add i8 %x, 2
+ %cmp = icmp ult i8 %off, 6
+ ret i1 %cmp
+}
+
+define i1 @range_check_intersection_to_icmp_sge(i8 range(i8 120, -128) %x) {
+; CHECK-LABEL: define i1 @range_check_intersection_to_icmp_sge(
+; CHECK-SAME: i8 range(i8 120, -128) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], -122
+; CHECK-NEXT: [[CMP:%.*]] = icmp sge i8 [[X]], 122
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add i8 %x, -122
+ %cmp = icmp ult i8 %off, 14
+ ret i1 %cmp
+}
+
+; Negative test: CmpCR relaxation cannot perform when x's range is nuw and nsw.
+define i1 @range_check_nsw_nuw(i8 range(i8 -20, -56) %x) {
+; CHECK-LABEL: define i1 @range_check_nsw_nuw(
+; CHECK-SAME: i8 range(i8 -20, -56) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add i8 [[X]], 20
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 14
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add i8 %x, 20
+ %cmp = icmp ult i8 %off, 14
+ ret i1 %cmp
+}
+
declare void @use(i8)
>From 4be1c34e10a4c538047f7c64eff8a9e0e4f0fd1c Mon Sep 17 00:00:00 2001
From: Camsyn <camsyn at foxmail.com>
Date: Mon, 23 Mar 2026 18:06:10 +0800
Subject: [PATCH 2/8] Relax 2-insts range check to one-icmp check
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 130 +++++++++++++++---
.../Transforms/SCCP/relax-range-checks.ll | 8 +-
2 files changed, 112 insertions(+), 26 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index fd315c14df866..c3414d63ada57 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -13,6 +13,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/SCCPSolver.h"
+#include "llvm/ADT/APInt.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
@@ -105,6 +106,96 @@ static ConstantRange getRange(Value *Op, SCCPSolver &Solver,
/*UndefAllowed=*/false);
}
+/// SCCP already proves x \in KnownCR, so only ActiveCmpCR = CmpCR ∩ KnownCR
+/// matters. Try to replace CmpCR with a simpler equivalent range NewCmpCR
+/// such that NewCmpCR ∩ KnownCR == ActiveCmpCR.
+///
+/// Prefer ranges that lower to a single canonical compare without an add:
+/// - [L, L+1) --> X eq L
+/// - [R+1, R) --> X ne R
+/// - [0, R) --> X ult R
+/// - [L, 0) --> X uge L
+/// - [SignMin, R) --> X slt R
+/// - [L, SignMin) --> X sge L
+///
+/// If no such range preserves the active semantics under KnownCR, keep CmpCR.
+static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
+ const ConstantRange &KnownCR) {
+ assert(!KnownCR.inverse().contains(CmpCR) &&
+ "CmpCR ∩ KnowCR should not be ∅");
+ assert((!CmpCR.isFullSet() && !CmpCR.isEmptySet()) && "Unexpected CmpCR");
+ assert((!KnownCR.isFullSet() && !KnownCR.isEmptySet()) &&
+ "Unexpected KnownCR");
+
+ // If KnownCR is both nuw and nsw, we cannot relax CmpCR at all.
+ if (KnownCR.isWrappedSet() && KnownCR.isSignWrappedSet())
+ return CmpCR;
+
+ const unsigned BW = CmpCR.getBitWidth();
+ // All reachable value satisfy CmpCR --> always true.
+ if (CmpCR.contains(KnownCR))
+ return ConstantRange::getFull(BW);
+
+ std::optional<ConstantRange> ActCmpCR = CmpCR.exactIntersectWith(KnownCR);
+ if (!ActCmpCR)
+ return CmpCR;
+
+ const APInt &CmpLo = ActCmpCR->getLower(), &CmpHi = ActCmpCR->getUpper();
+
+ // If the intersection happens to be the ONE-icmp check, just return it.
+ if (/*eq*/ ActCmpCR->isSingleElement() ||
+ /*ne*/ ActCmpCR->inverse().isSingleElement() ||
+ /*ult*/ CmpLo.isZero() ||
+ /*slt*/ CmpLo.isMinSignedValue() ||
+ /*uge*/ CmpHi.isZero() ||
+ /*sge*/ CmpHi.isMinSignedValue())
+ return *ActCmpCR;
+
+ const APInt Zero = APInt::getZero(BW);
+ const APInt SignMin = APInt::getSignedMinValue(BW);
+
+ if (CmpLo == KnownCR.getLower()) {
+ // Tie to lower:
+
+ // Try ult
+ // 0
+ // | L------------R : KnownCR
+ // | L---R : ActiveCmpCR
+ // L------R : RelaxedCmpCR
+ if (!KnownCR.isWrappedSet())
+ return ConstantRange::getNonEmpty(Zero, CmpHi);
+
+ // Try slt
+ // smin smin
+ // -----R | L------- : KnownCR ----R | L------- : KnownCR
+ // | L--R : ActiveCmpCR --R | L------- : ActiveCmpCR
+ // L-----R : RelaxedCmpCR --R L---------- : RelaxedCmpCR
+ if (!KnownCR.isSignWrappedSet())
+ return ConstantRange::getNonEmpty(SignMin, CmpHi);
+
+ } else if (CmpHi == KnownCR.getUpper()) {
+ // Tie to upper:
+
+ // Try uge
+ // 0
+ // | L--------R : KnownCR
+ // | L---R : ActiveCmpCR
+ // R L---------- : RelaxedCmpCR
+ if (!KnownCR.isWrappedSet())
+ return ConstantRange::getNonEmpty(CmpLo, Zero);
+
+ // Try sge
+ // smin smin
+ // -----R | L------- : KnownCR -----R | L------- : KnownCR
+ // L--R | : ActiveCmpCR -----R | L--- : ActiveCmpCR
+ // L-----R : RelaxedCmpCR --------R L--- : RelaxedCmpCR
+ if (!KnownCR.isSignWrappedSet())
+ return ConstantRange::getNonEmpty(CmpLo, SignMin);
+ }
+
+ return CmpCR;
+}
+
/// Try to use \p Inst's value range from \p Solver to infer the NUW flag.
static bool refineInstruction(SCCPSolver &Solver,
const SmallPtrSetImpl<Value *> &InsertedValues,
@@ -318,29 +409,24 @@ static Value *simplifyInstruction(SCCPSolver &Solver,
// Early exit if we know nothing about X.
if (LRange.isFullSet())
return nullptr;
- 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;
- };
// 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 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.
- if (auto *V = ConvertCRToICmp(CR->exactUnionWith(LRange.inverse())))
- return V;
+ // of range inputs. Based on this, try to simplify CmpCR as a single
+ // ult/uge/slt/sge/eq/ne.
+ // E.g., CmpCR = [3, 10), LRange = [5, 0) --> NewCmpCR = [0, 10) -> ult
+ ConstantRange NewCmpCR = simplifyCmpRange(*CR, LRange);
+
+ ICmpInst::Predicate Pred;
+ APInt RHS;
+ // If NewCmpCR is just the same as CR, no simplification happens.
+ if (NewCmpCR != *CR) {
+ bool Match [[maybe_unused]] = NewCmpCR.getEquivalentICmp(Pred, RHS);
+ assert(Match && "Incorrect simplifyCmpRange");
+ IRBuilder<NoFolder> Builder(&Inst);
+ Value *NewICmp =
+ Builder.CreateICmp(Pred, X, ConstantInt::get(X->getType(), RHS));
+ InsertedValues.insert(NewICmp);
+ return NewICmp;
+ }
}
}
diff --git a/llvm/test/Transforms/SCCP/relax-range-checks.ll b/llvm/test/Transforms/SCCP/relax-range-checks.ll
index f7c4f6f468929..998271b3b24d9 100644
--- a/llvm/test/Transforms/SCCP/relax-range-checks.ll
+++ b/llvm/test/Transforms/SCCP/relax-range-checks.ll
@@ -117,7 +117,7 @@ define i1 @range_check_to_icmp_ult(i8 range(i8 2, 10) %x) {
; CHECK-LABEL: define i1 @range_check_to_icmp_ult(
; CHECK-SAME: i8 range(i8 2, 10) [[X:%.*]]) {
; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], -2
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 4
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[X]], 6
; CHECK-NEXT: ret i1 [[CMP]]
;
%off = add i8 %x, -2
@@ -129,7 +129,7 @@ define i1 @range_check_to_icmp_uge(i8 range(i8 2, 6) %x) {
; CHECK-LABEL: define i1 @range_check_to_icmp_uge(
; CHECK-SAME: i8 range(i8 2, 6) [[X:%.*]]) {
; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], -4
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 2
+; CHECK-NEXT: [[CMP:%.*]] = icmp uge i8 [[X]], 4
; CHECK-NEXT: ret i1 [[CMP]]
;
%off = add nsw i8 %x, -4
@@ -141,7 +141,7 @@ define i1 @range_check_to_icmp_slt(i8 range(i8 -56, 20) %x) {
; CHECK-LABEL: define i1 @range_check_to_icmp_slt(
; CHECK-SAME: i8 range(i8 -56, 20) [[X:%.*]]) {
; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], 56
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 50
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[X]], -6
; CHECK-NEXT: ret i1 [[CMP]]
;
%off = add nsw i8 %x, 56
@@ -153,7 +153,7 @@ define i1 @range_check_to_icmp_sge(i8 range(i8 -56, 20) %x) {
; CHECK-LABEL: define i1 @range_check_to_icmp_sge(
; CHECK-SAME: i8 range(i8 -56, 20) [[X:%.*]]) {
; CHECK-NEXT: [[OFF:%.*]] = add nsw i8 [[X]], 16
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[OFF]], 36
+; CHECK-NEXT: [[CMP:%.*]] = icmp sge i8 [[X]], -16
; CHECK-NEXT: ret i1 [[CMP]]
;
%off = add nsw i8 %x, 16
>From 2c5b36424159b3dbdfe0bf0baf68626f3da6088c Mon Sep 17 00:00:00 2001
From: Camsyn <camsyn at foxmail.com>
Date: Tue, 24 Mar 2026 21:14:03 +0800
Subject: [PATCH 3/8] fix: CmpCR could be simple enough
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index c3414d63ada57..206b4dc0a7691 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -13,7 +13,6 @@
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/SCCPSolver.h"
-#include "llvm/ADT/APInt.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
@@ -417,10 +416,8 @@ static Value *simplifyInstruction(SCCPSolver &Solver,
ICmpInst::Predicate Pred;
APInt RHS;
- // If NewCmpCR is just the same as CR, no simplification happens.
- if (NewCmpCR != *CR) {
- bool Match [[maybe_unused]] = NewCmpCR.getEquivalentICmp(Pred, RHS);
- assert(Match && "Incorrect simplifyCmpRange");
+ // NewCmpCR might be CmpCR, i.e., no simplification happens.
+ if (NewCmpCR.getEquivalentICmp(Pred, RHS)) {
IRBuilder<NoFolder> Builder(&Inst);
Value *NewICmp =
Builder.CreateICmp(Pred, X, ConstantInt::get(X->getType(), RHS));
>From 6554b14e65496cfbf4f416cfe3ab646dae958912 Mon Sep 17 00:00:00 2001
From: Camsyn <camsyn at foxmail.com>
Date: Tue, 24 Mar 2026 23:44:23 +0800
Subject: [PATCH 4/8] fix: move a guard to its proper location
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 206b4dc0a7691..44a11fb2d745f 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -126,10 +126,6 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
assert((!KnownCR.isFullSet() && !KnownCR.isEmptySet()) &&
"Unexpected KnownCR");
- // If KnownCR is both nuw and nsw, we cannot relax CmpCR at all.
- if (KnownCR.isWrappedSet() && KnownCR.isSignWrappedSet())
- return CmpCR;
-
const unsigned BW = CmpCR.getBitWidth();
// All reachable value satisfy CmpCR --> always true.
if (CmpCR.contains(KnownCR))
@@ -150,6 +146,10 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
/*sge*/ CmpHi.isMinSignedValue())
return *ActCmpCR;
+ // If KnownCR is both nuw and nsw, we cannot relax CmpCR at all.
+ if (KnownCR.isWrappedSet() && KnownCR.isSignWrappedSet())
+ return CmpCR;
+
const APInt Zero = APInt::getZero(BW);
const APInt SignMin = APInt::getSignedMinValue(BW);
>From 42f845f62ff5ce8578613ddb64678fc740c03fe7 Mon Sep 17 00:00:00 2001
From: Camsyn <camsyn at foxmail.com>
Date: Wed, 25 Mar 2026 00:41:38 +0800
Subject: [PATCH 5/8] fix: suport ne relaxing
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 44a11fb2d745f..62f49dd7f6a2a 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -146,16 +146,19 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
/*sge*/ CmpHi.isMinSignedValue())
return *ActCmpCR;
- // If KnownCR is both nuw and nsw, we cannot relax CmpCR at all.
- if (KnownCR.isWrappedSet() && KnownCR.isSignWrappedSet())
- return CmpCR;
-
const APInt Zero = APInt::getZero(BW);
const APInt SignMin = APInt::getSignedMinValue(BW);
if (CmpLo == KnownCR.getLower()) {
// Tie to lower:
+ // Try ne
+ // L------------R : KnownCR
+ // L-----------R : ActiveCmpCR
+ // ---------------RL-- : RelaxedCmpCR
+ if (CmpHi + 1 == KnownCR.getUpper())
+ return ConstantRange::getNonEmpty(KnownCR.getUpper(), CmpHi);
+
// Try ult
// 0
// | L------------R : KnownCR
@@ -175,6 +178,14 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
} else if (CmpHi == KnownCR.getUpper()) {
// Tie to upper:
+ // Try ne
+ //
+ // L--------R : KnownCR
+ // L-------R : ActiveCmpCR
+ // ---RL-------------- : RelaxedCmpCR
+ if (KnownCR.getLower() + 1 == CmpLo)
+ return ConstantRange::getNonEmpty(CmpLo, KnownCR.getLower());
+
// Try uge
// 0
// | L--------R : KnownCR
>From 756d74fcf107c5df3f7d02885d3b6a62a32c7acc Mon Sep 17 00:00:00 2001
From: Camsyn <camsyn at foxmail.com>
Date: Wed, 25 Mar 2026 20:42:11 +0800
Subject: [PATCH 6/8] fix: prefer ne rather than ge/lt
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 45 ++++++++++++------------
1 file changed, 23 insertions(+), 22 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 62f49dd7f6a2a..cfbf733eb52c8 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -134,13 +134,29 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
std::optional<ConstantRange> ActCmpCR = CmpCR.exactIntersectWith(KnownCR);
if (!ActCmpCR)
return CmpCR;
+ // Proof of ActCmpCR cannot be ne:
+ // 1. ActCmpCR = ne ∧ ActCmpCR ⊆ KnownCR -> KnownCR = ActCmpCR/fullset
+ // 2. KnownCR = fullset contradicts KnownCR != fullset
+ // 3. KnownCR = ActCmpCR = KnownCR ∩ CmpCR -> KnownCR ⊆ CmpCR
+ // 4. KnownCR ⊆ CmpCR contradicts KnownCR ⊈ CmpCR
+ assert(/*ne*/ !ActCmpCR->inverse().isSingleElement() && "Unexpected ne");
+
+ // We prefer eq rather than ne.
+ if (/*eq*/ ActCmpCR->isSingleElement())
+ return *ActCmpCR;
+
+ // We prefer ne rather than lt/ge.
+ // L--------R : KnownCR or L------------R : KnownCR
+ // L-------R : ActiveCmpCR L-----------R : ActiveCmpCR
+ // ---RL-------------- : RelaxedCmpCR ---------------RL-- : RelaxedCmpCR
+ if (const ConstantRange FalseCR = KnownCR.intersectWith(ActCmpCR->inverse());
+ FalseCR.isSingleElement())
+ return FalseCR.inverse();
const APInt &CmpLo = ActCmpCR->getLower(), &CmpHi = ActCmpCR->getUpper();
// If the intersection happens to be the ONE-icmp check, just return it.
- if (/*eq*/ ActCmpCR->isSingleElement() ||
- /*ne*/ ActCmpCR->inverse().isSingleElement() ||
- /*ult*/ CmpLo.isZero() ||
+ if (/*ult*/ CmpLo.isZero() ||
/*slt*/ CmpLo.isMinSignedValue() ||
/*uge*/ CmpHi.isZero() ||
/*sge*/ CmpHi.isMinSignedValue())
@@ -152,14 +168,7 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
if (CmpLo == KnownCR.getLower()) {
// Tie to lower:
- // Try ne
- // L------------R : KnownCR
- // L-----------R : ActiveCmpCR
- // ---------------RL-- : RelaxedCmpCR
- if (CmpHi + 1 == KnownCR.getUpper())
- return ConstantRange::getNonEmpty(KnownCR.getUpper(), CmpHi);
-
- // Try ult
+ // Try ult.
// 0
// | L------------R : KnownCR
// | L---R : ActiveCmpCR
@@ -167,7 +176,7 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
if (!KnownCR.isWrappedSet())
return ConstantRange::getNonEmpty(Zero, CmpHi);
- // Try slt
+ // Try slt.
// smin smin
// -----R | L------- : KnownCR ----R | L------- : KnownCR
// | L--R : ActiveCmpCR --R | L------- : ActiveCmpCR
@@ -178,15 +187,7 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
} else if (CmpHi == KnownCR.getUpper()) {
// Tie to upper:
- // Try ne
- //
- // L--------R : KnownCR
- // L-------R : ActiveCmpCR
- // ---RL-------------- : RelaxedCmpCR
- if (KnownCR.getLower() + 1 == CmpLo)
- return ConstantRange::getNonEmpty(CmpLo, KnownCR.getLower());
-
- // Try uge
+ // Try uge.
// 0
// | L--------R : KnownCR
// | L---R : ActiveCmpCR
@@ -194,7 +195,7 @@ static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
if (!KnownCR.isWrappedSet())
return ConstantRange::getNonEmpty(CmpLo, Zero);
- // Try sge
+ // Try sge.
// smin smin
// -----R | L------- : KnownCR -----R | L------- : KnownCR
// L--R | : ActiveCmpCR -----R | L--- : ActiveCmpCR
>From a918eb2758a81a7c9fb0c565edc7bf57d8113622 Mon Sep 17 00:00:00 2001
From: Camsyn <camsyn at foxmail.com>
Date: Tue, 31 Mar 2026 19:30:34 +0800
Subject: [PATCH 7/8] Fix: correct assertion
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index cfbf733eb52c8..d19135537ad85 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -120,16 +120,20 @@ static ConstantRange getRange(Value *Op, SCCPSolver &Solver,
/// If no such range preserves the active semantics under KnownCR, keep CmpCR.
static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
const ConstantRange &KnownCR) {
- assert(!KnownCR.inverse().contains(CmpCR) &&
- "CmpCR ∩ KnowCR should not be ∅");
assert((!CmpCR.isFullSet() && !CmpCR.isEmptySet()) && "Unexpected CmpCR");
- assert((!KnownCR.isFullSet() && !KnownCR.isEmptySet()) &&
- "Unexpected KnownCR");
+ assert(!KnownCR.isEmptySet() && "Unexpected KnownCR");
+
+ // If KnownCR is full, bail out early.
+ if (KnownCR.isFullSet())
+ return CmpCR;
const unsigned BW = CmpCR.getBitWidth();
- // All reachable value satisfy CmpCR --> always true.
+ // All reachable values satisfy CmpCR --> always true.
if (CmpCR.contains(KnownCR))
return ConstantRange::getFull(BW);
+ // All values in CmpCR are unreachable --> always false.
+ if (KnownCR.inverse().contains(CmpCR))
+ return ConstantRange::getEmpty(BW);
std::optional<ConstantRange> ActCmpCR = CmpCR.exactIntersectWith(KnownCR);
if (!ActCmpCR)
>From a58bcf12007c4da94e9e66644816563ecb56602f Mon Sep 17 00:00:00 2001
From: Camsyn <camsyn at foxmail.com>
Date: Fri, 1 May 2026 17:14:39 +0800
Subject: [PATCH 8/8] Handle empty/full SCCP relaxed comparison ranges
---
llvm/lib/Transforms/Utils/SCCPSolver.cpp | 5 +++-
.../Transforms/SCCP/relax-range-checks.ll | 24 +++++++++++++++++++
2 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index d19135537ad85..5b9cf1e97fcd1 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -120,9 +120,12 @@ static ConstantRange getRange(Value *Op, SCCPSolver &Solver,
/// If no such range preserves the active semantics under KnownCR, keep CmpCR.
static ConstantRange simplifyCmpRange(const ConstantRange &CmpCR,
const ConstantRange &KnownCR) {
- assert((!CmpCR.isFullSet() && !CmpCR.isEmptySet()) && "Unexpected CmpCR");
assert(!KnownCR.isEmptySet() && "Unexpected KnownCR");
+ // Empty and full ranges already lower to a single icmp.
+ if (CmpCR.isEmptySet() || CmpCR.isFullSet())
+ return CmpCR;
+
// If KnownCR is full, bail out early.
if (KnownCR.isFullSet())
return CmpCR;
diff --git a/llvm/test/Transforms/SCCP/relax-range-checks.ll b/llvm/test/Transforms/SCCP/relax-range-checks.ll
index 998271b3b24d9..189cde8fb6061 100644
--- a/llvm/test/Transforms/SCCP/relax-range-checks.ll
+++ b/llvm/test/Transforms/SCCP/relax-range-checks.ll
@@ -161,6 +161,30 @@ define i1 @range_check_to_icmp_sge(i8 range(i8 -56, 20) %x) {
ret i1 %cmp
}
+define i1 @range_check_to_icmp_empty(i8 range(i8 2, 10) %x) {
+; CHECK-LABEL: define i1 @range_check_to_icmp_empty(
+; CHECK-SAME: i8 range(i8 2, 10) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nuw nsw i8 [[X]], -2
+; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[X]], 0
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add nuw i8 %x, -2
+ %cmp = icmp ult i8 %off, 0
+ ret i1 %cmp
+}
+
+define i1 @range_check_to_icmp_full(i8 range(i8 2, 10) %x) {
+; CHECK-LABEL: define i1 @range_check_to_icmp_full(
+; CHECK-SAME: i8 range(i8 2, 10) [[X:%.*]]) {
+; CHECK-NEXT: [[OFF:%.*]] = add nuw nsw i8 [[X]], -2
+; CHECK-NEXT: [[CMP:%.*]] = icmp uge i8 [[X]], 0
+; CHECK-NEXT: ret i1 [[CMP]]
+;
+ %off = add nuw i8 %x, -2
+ %cmp = icmp uge i8 %off, 0
+ ret i1 %cmp
+}
+
; Cover the early exit when ActiveCmpCR is already a one-icmp check.
define i1 @range_check_intersection_to_icmp_eq(i32 range(i32 0, 4) %x) {
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