[llvm] [CVP] Keep `ReachableCaseCount` in sync with range of condition (PR #142302)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Sat May 31 23:15:27 PDT 2025
https://github.com/dtcxzyw updated https://github.com/llvm/llvm-project/pull/142302
>From 50c01fd2a32cd16216208c7d5f441f716aede22d Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sun, 1 Jun 2025 12:35:14 +0800
Subject: [PATCH 1/3] [CVP] Add pre-commit tests. NFC.
---
.../CorrelatedValuePropagation/switch.ll | 38 +++++++++++++++++++
1 file changed, 38 insertions(+)
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/switch.ll b/llvm/test/Transforms/CorrelatedValuePropagation/switch.ll
index a0794d5efe932..456807bc499f8 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/switch.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/switch.ll
@@ -294,6 +294,44 @@ cleanup:
ret i32 %retval.0
}
+; Make sure that we don't branch into unreachable.
+
+define void @pr142286() {
+; CHECK-LABEL: define void @pr142286() {
+; CHECK-NEXT: start:
+; CHECK-NEXT: br label [[LOOP:%.*]]
+; CHECK: loop:
+; CHECK-NEXT: br label [[LOOP2:%.*]]
+; CHECK: loop2:
+; CHECK-NEXT: br label [[LOOP3:%.*]]
+; CHECK: loop3:
+; CHECK-NEXT: br label [[DEFAULT_UNREACHABLE:%.*]]
+; CHECK: default.unreachable:
+; CHECK-NEXT: unreachable
+; CHECK: exit:
+; CHECK-NEXT: ret void
+;
+start:
+ br label %loop
+
+loop:
+ %phi = phi i8 [ -1, %start ], [ 0, %loop3 ]
+ br label %loop2
+
+loop2:
+ br label %loop3
+
+loop3:
+ switch i8 %phi, label %exit [
+ i8 0, label %loop3
+ i8 1, label %loop2
+ i8 2, label %loop
+ ]
+
+exit:
+ ret void
+}
+
declare i32 @call0()
declare i32 @call1()
declare i32 @call2()
>From 4686664f341d5f5ea13b4bd625b69e612d6db1f9 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sun, 1 Jun 2025 12:39:11 +0800
Subject: [PATCH 2/3] [CVP] Keep ReachableCaseCount in sync with range of
condition
---
llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp | 8 +++++---
llvm/test/Transforms/CorrelatedValuePropagation/switch.ll | 4 +---
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 5226aeb66f65a..4228d0529dc13 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -370,7 +370,7 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
{ // Scope for SwitchInstProfUpdateWrapper. It must not live during
// ConstantFoldTerminator() as the underlying SwitchInst can be changed.
SwitchInstProfUpdateWrapper SI(*I);
- unsigned ReachableCaseCount = 0;
+ SmallVector<APInt, 4> ReachableCaseValues;
for (auto CI = SI->case_begin(), CE = SI->case_end(); CI != CE;) {
ConstantInt *Case = CI->getCaseValue();
@@ -407,13 +407,15 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
// Increment the case iterator since we didn't delete it.
++CI;
- ++ReachableCaseCount;
+ ReachableCaseValues.push_back(Case->getValue());
}
- if (ReachableCaseCount > 1 && !SI->defaultDestUnreachable()) {
+ if (ReachableCaseValues.size() > 1 && !SI->defaultDestUnreachable()) {
BasicBlock *DefaultDest = SI->getDefaultDest();
ConstantRange CR = LVI->getConstantRangeAtUse(I->getOperandUse(0),
/*UndefAllowed*/ false);
+ unsigned ReachableCaseCount = count_if(
+ ReachableCaseValues, [&](const APInt &V) { return CR.contains(V); });
// The default dest is unreachable if all cases are covered.
if (!CR.isSizeLargerThan(ReachableCaseCount)) {
BasicBlock *NewUnreachableBB =
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/switch.ll b/llvm/test/Transforms/CorrelatedValuePropagation/switch.ll
index 456807bc499f8..7e6aa3eeebe20 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/switch.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/switch.ll
@@ -305,9 +305,7 @@ define void @pr142286() {
; CHECK: loop2:
; CHECK-NEXT: br label [[LOOP3:%.*]]
; CHECK: loop3:
-; CHECK-NEXT: br label [[DEFAULT_UNREACHABLE:%.*]]
-; CHECK: default.unreachable:
-; CHECK-NEXT: unreachable
+; CHECK-NEXT: br label [[EXIT:%.*]]
; CHECK: exit:
; CHECK-NEXT: ret void
;
>From e2f18f46e9a1f4b63d488c60350216e88fc3439b Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sun, 1 Jun 2025 14:15:00 +0800
Subject: [PATCH 3/3] [CVP] Always compute CR
---
.../Scalar/CorrelatedValuePropagation.cpp | 66 +++++++++++--------
1 file changed, 38 insertions(+), 28 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 4228d0529dc13..b95a851c99b49 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -370,15 +370,30 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
{ // Scope for SwitchInstProfUpdateWrapper. It must not live during
// ConstantFoldTerminator() as the underlying SwitchInst can be changed.
SwitchInstProfUpdateWrapper SI(*I);
- SmallVector<APInt, 4> ReachableCaseValues;
+ ConstantRange CR =
+ LVI->getConstantRangeAtUse(I->getOperandUse(0), /*UndefAllowed=*/false);
+ unsigned ReachableCaseCount = 0;
for (auto CI = SI->case_begin(), CE = SI->case_end(); CI != CE;) {
ConstantInt *Case = CI->getCaseValue();
- auto *Res = dyn_cast_or_null<ConstantInt>(
- LVI->getPredicateAt(CmpInst::ICMP_EQ, Cond, Case, I,
- /* UseBlockValue */ true));
+ std::optional<bool> Predicate = std::nullopt;
+ if (!CR.contains(Case->getValue()))
+ Predicate = false;
+ else if (CR.isSingleElement() &&
+ *CR.getSingleElement() == Case->getValue())
+ Predicate = true;
+ if (!Predicate) {
+ // Handle missing cases, e.g., the range has a hole.
+ auto *Res = dyn_cast_or_null<ConstantInt>(
+ LVI->getPredicateAt(CmpInst::ICMP_EQ, Cond, Case, I,
+ /* UseBlockValue=*/true));
+ if (Res && Res->isZero())
+ Predicate = false;
+ else if (Res && Res->isOne())
+ Predicate = true;
+ }
- if (Res && Res->isZero()) {
+ if (Predicate && !*Predicate) {
// This case never fires - remove it.
BasicBlock *Succ = CI->getCaseSuccessor();
Succ->removePredecessor(BB);
@@ -395,7 +410,7 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
DTU.applyUpdatesPermissive({{DominatorTree::Delete, BB, Succ}});
continue;
}
- if (Res && Res->isOne()) {
+ if (Predicate && *Predicate) {
// This case always fires. Arrange for the switch to be turned into an
// unconditional branch by replacing the switch condition with the case
// value.
@@ -407,32 +422,27 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
// Increment the case iterator since we didn't delete it.
++CI;
- ReachableCaseValues.push_back(Case->getValue());
+ ++ReachableCaseCount;
}
- if (ReachableCaseValues.size() > 1 && !SI->defaultDestUnreachable()) {
+ // The default dest is unreachable if all cases are covered.
+ if (!SI->defaultDestUnreachable() &&
+ !CR.isSizeLargerThan(ReachableCaseCount)) {
BasicBlock *DefaultDest = SI->getDefaultDest();
- ConstantRange CR = LVI->getConstantRangeAtUse(I->getOperandUse(0),
- /*UndefAllowed*/ false);
- unsigned ReachableCaseCount = count_if(
- ReachableCaseValues, [&](const APInt &V) { return CR.contains(V); });
- // The default dest is unreachable if all cases are covered.
- if (!CR.isSizeLargerThan(ReachableCaseCount)) {
- BasicBlock *NewUnreachableBB =
- BasicBlock::Create(BB->getContext(), "default.unreachable",
- BB->getParent(), DefaultDest);
- new UnreachableInst(BB->getContext(), NewUnreachableBB);
-
- DefaultDest->removePredecessor(BB);
- SI->setDefaultDest(NewUnreachableBB);
-
- if (SuccessorsCount[DefaultDest] == 1)
- DTU.applyUpdates({{DominatorTree::Delete, BB, DefaultDest}});
- DTU.applyUpdates({{DominatorTree::Insert, BB, NewUnreachableBB}});
+ BasicBlock *NewUnreachableBB =
+ BasicBlock::Create(BB->getContext(), "default.unreachable",
+ BB->getParent(), DefaultDest);
+ new UnreachableInst(BB->getContext(), NewUnreachableBB);
- ++NumDeadCases;
- Changed = true;
- }
+ DefaultDest->removePredecessor(BB);
+ SI->setDefaultDest(NewUnreachableBB);
+
+ if (SuccessorsCount[DefaultDest] == 1)
+ DTU.applyUpdates({{DominatorTree::Delete, BB, DefaultDest}});
+ DTU.applyUpdates({{DominatorTree::Insert, BB, NewUnreachableBB}});
+
+ ++NumDeadCases;
+ Changed = true;
}
}
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