[llvm] [AA][JumpThreading] Don't use DomTree for AA in JumpThreading (PR #79294)
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Wed Jan 24 06:09:36 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Nikita Popov (nikic)
<details>
<summary>Changes</summary>
JumpThreading may perform AA queries while the dominator tree is not up to date, which may result in miscompilations.
Fix this by adding a new AAQI option to disable the use of the dominator tree in BasicAA.
Fixes https://github.com/llvm/llvm-project/issues/79175.
---
Full diff: https://github.com/llvm/llvm-project/pull/79294.diff
5 Files Affected:
- (modified) llvm/include/llvm/Analysis/AliasAnalysis.h (+9)
- (modified) llvm/include/llvm/Analysis/BasicAliasAnalysis.h (+9-4)
- (modified) llvm/lib/Analysis/BasicAliasAnalysis.cpp (+4-2)
- (modified) llvm/lib/Transforms/Scalar/JumpThreading.cpp (+2)
- (modified) llvm/test/Transforms/JumpThreading/pr79175.ll (+1-3)
``````````diff
diff --git a/llvm/include/llvm/Analysis/AliasAnalysis.h b/llvm/include/llvm/Analysis/AliasAnalysis.h
index d6f732d35fd4cd..fbf1f7a4a06203 100644
--- a/llvm/include/llvm/Analysis/AliasAnalysis.h
+++ b/llvm/include/llvm/Analysis/AliasAnalysis.h
@@ -287,6 +287,10 @@ class AAQueryInfo {
/// store %l, ...
bool MayBeCrossIteration = false;
+ /// Whether alias analysis is allowed to use the dominator tree, for use by
+ /// passes that lazily update the DT while performing AA queries.
+ bool UseDominatorTree = true;
+
AAQueryInfo(AAResults &AAR, CaptureInfo *CI) : AAR(AAR), CI(CI) {}
};
@@ -668,6 +672,11 @@ class BatchAAResults {
void enableCrossIterationMode() {
AAQI.MayBeCrossIteration = true;
}
+
+ /// Disable the use of the dominator tree during alias analysis queries.
+ void disableDominatorTree() {
+ AAQI.UseDominatorTree = false;
+ }
};
/// Temporary typedef for legacy code that uses a generic \c AliasAnalysis
diff --git a/llvm/include/llvm/Analysis/BasicAliasAnalysis.h b/llvm/include/llvm/Analysis/BasicAliasAnalysis.h
index afc1811239f283..4a1608e7be6522 100644
--- a/llvm/include/llvm/Analysis/BasicAliasAnalysis.h
+++ b/llvm/include/llvm/Analysis/BasicAliasAnalysis.h
@@ -43,20 +43,25 @@ class BasicAAResult : public AAResultBase {
const Function &F;
const TargetLibraryInfo &TLI;
AssumptionCache &AC;
- DominatorTree *DT;
+ // Don't access this directly, use getDT() instead.
+ DominatorTree *DT_;
+
+ DominatorTree *getDT(const AAQueryInfo &AAQI) const {
+ return AAQI.UseDominatorTree ? DT_ : nullptr;
+ }
public:
BasicAAResult(const DataLayout &DL, const Function &F,
const TargetLibraryInfo &TLI, AssumptionCache &AC,
DominatorTree *DT = nullptr)
- : DL(DL), F(F), TLI(TLI), AC(AC), DT(DT) {}
+ : DL(DL), F(F), TLI(TLI), AC(AC), DT_(DT) {}
BasicAAResult(const BasicAAResult &Arg)
: AAResultBase(Arg), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI), AC(Arg.AC),
- DT(Arg.DT) {}
+ DT_(Arg.DT_) {}
BasicAAResult(BasicAAResult &&Arg)
: AAResultBase(std::move(Arg)), DL(Arg.DL), F(Arg.F), TLI(Arg.TLI),
- AC(Arg.AC), DT(Arg.DT) {}
+ AC(Arg.AC), DT_(Arg.DT_) {}
/// Handle invalidation events in the new pass manager.
bool invalidate(Function &Fn, const PreservedAnalyses &PA,
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 3178e2d2781674..1028b52a79123f 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -89,7 +89,7 @@ bool BasicAAResult::invalidate(Function &Fn, const PreservedAnalyses &PA,
// may be created without handles to some analyses and in that case don't
// depend on them.
if (Inv.invalidate<AssumptionAnalysis>(Fn, PA) ||
- (DT && Inv.invalidate<DominatorTreeAnalysis>(Fn, PA)))
+ (DT_ && Inv.invalidate<DominatorTreeAnalysis>(Fn, PA)))
return true;
// Otherwise this analysis result remains valid.
@@ -1063,6 +1063,7 @@ AliasResult BasicAAResult::aliasGEP(
: AliasResult::MayAlias;
}
+ DominatorTree *DT = getDT(AAQI);
DecomposedGEP DecompGEP1 = DecomposeGEPExpression(GEP1, DL, &AC, DT);
DecomposedGEP DecompGEP2 = DecomposeGEPExpression(V2, DL, &AC, DT);
@@ -1556,6 +1557,7 @@ AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
const Value *HintO1 = getUnderlyingObject(Hint1);
const Value *HintO2 = getUnderlyingObject(Hint2);
+ DominatorTree *DT = getDT(AAQI);
auto ValidAssumeForPtrContext = [&](const Value *Ptr) {
if (const Instruction *PtrI = dyn_cast<Instruction>(Ptr)) {
return isValidAssumeForContext(Assume, PtrI, DT,
@@ -1735,7 +1737,7 @@ bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V,
if (!Inst || Inst->getParent()->isEntryBlock())
return true;
- return isNotInCycle(Inst, DT, /*LI*/ nullptr);
+ return isNotInCycle(Inst, getDT(AAQI), /*LI*/ nullptr);
}
/// Computes the symbolic difference between two de-composed GEPs.
diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index b7cf0248963156..bb33a5da288ce9 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1261,6 +1261,8 @@ bool JumpThreadingPass::simplifyPartiallyRedundantLoad(LoadInst *LoadI) {
BasicBlock::iterator BBIt(LoadI);
bool IsLoadCSE;
BatchAAResults BatchAA(*AA);
+ // The dominator tree is updated lazily and may not be valid at this point.
+ BatchAA.disableDominatorTree();
if (Value *AvailableVal = FindAvailableLoadedValue(
LoadI, LoadBB, BBIt, DefMaxInstsToScan, &BatchAA, &IsLoadCSE)) {
// If the value of the load is locally available within the block, just use
diff --git a/llvm/test/Transforms/JumpThreading/pr79175.ll b/llvm/test/Transforms/JumpThreading/pr79175.ll
index 6815aabb26dfc6..2c7ee0770cdc73 100644
--- a/llvm/test/Transforms/JumpThreading/pr79175.ll
+++ b/llvm/test/Transforms/JumpThreading/pr79175.ll
@@ -4,7 +4,6 @@
@f = external global i32
; Make sure the value of @f is reloaded prior to the final comparison.
-; FIXME: This is a miscompile.
define i32 @test(i64 %idx, i32 %val) {
; CHECK-LABEL: define i32 @test(
; CHECK-SAME: i64 [[IDX:%.*]], i32 [[VAL:%.*]]) {
@@ -20,13 +19,12 @@ define i32 @test(i64 %idx, i32 %val) {
; CHECK-NEXT: [[COND_FR:%.*]] = freeze i1 [[CMP_I]]
; CHECK-NEXT: br i1 [[COND_FR]], label [[COND_END_THREAD]], label [[TMP0:%.*]]
; CHECK: cond.end.thread:
-; CHECK-NEXT: [[F_RELOAD_PR:%.*]] = load i32, ptr @f, align 4
; CHECK-NEXT: br label [[TMP0]]
; CHECK: 0:
-; CHECK-NEXT: [[F_RELOAD:%.*]] = phi i32 [ [[F]], [[COND_END]] ], [ [[F_RELOAD_PR]], [[COND_END_THREAD]] ]
; CHECK-NEXT: [[TMP1:%.*]] = phi i32 [ 0, [[COND_END_THREAD]] ], [ [[VAL]], [[COND_END]] ]
; CHECK-NEXT: [[F_IDX:%.*]] = getelementptr inbounds i32, ptr @f, i64 [[IDX]]
; CHECK-NEXT: store i32 [[TMP1]], ptr [[F_IDX]], align 4
+; CHECK-NEXT: [[F_RELOAD:%.*]] = load i32, ptr @f, align 4
; CHECK-NEXT: [[CMP3:%.*]] = icmp slt i32 [[F_RELOAD]], 1
; CHECK-NEXT: br i1 [[CMP3]], label [[RETURN2:%.*]], label [[RETURN]]
; CHECK: return:
``````````
</details>
https://github.com/llvm/llvm-project/pull/79294
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