[llvm] [DSE] Use CycleInfo instead of LoopInfo (PR #188253)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Wed Mar 25 07:26:21 PDT 2026
https://github.com/nikic updated https://github.com/llvm/llvm-project/pull/188253
>From 1f3816249af3473b5114d785da0d080b4d980026 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Mon, 16 Mar 2026 17:49:35 +0100
Subject: [PATCH 1/2] [DSE] Use CycleInfo instead of LoopInfo
DSE needs to reason about cycles in order to correctly handle
loop-carried dependencies. It currently does this by using LoopInfo
and performing a separate check for irreducible control flow.
Instead, we can use CycleInfo, which is like LoopInfo but also
handles irreducible cycles.
This requires computing CycleInfo (which, unlike LoopInfo won't
be reused by surrouding passes), but ends up being neutral in
terms of compile-time overall.
---
llvm/include/llvm/Analysis/AliasAnalysis.h | 7 ++-
llvm/lib/Analysis/BasicAliasAnalysis.cpp | 12 +++--
.../Scalar/DeadStoreElimination.cpp | 45 ++++++++-----------
llvm/test/Other/new-pm-defaults.ll | 1 +
llvm/test/Other/new-pm-lto-defaults.ll | 1 +
.../Other/new-pm-thinlto-postlink-defaults.ll | 1 +
.../new-pm-thinlto-postlink-pgo-defaults.ll | 1 +
...-pm-thinlto-postlink-samplepgo-defaults.ll | 1 +
.../Other/new-pm-thinlto-prelink-defaults.ll | 1 +
.../new-pm-thinlto-prelink-pgo-defaults.ll | 1 +
...w-pm-thinlto-prelink-samplepgo-defaults.ll | 1 +
11 files changed, 39 insertions(+), 33 deletions(-)
diff --git a/llvm/include/llvm/Analysis/AliasAnalysis.h b/llvm/include/llvm/Analysis/AliasAnalysis.h
index d9d8ac797688d..1bd6fc48da289 100644
--- a/llvm/include/llvm/Analysis/AliasAnalysis.h
+++ b/llvm/include/llvm/Analysis/AliasAnalysis.h
@@ -57,6 +57,7 @@ class AtomicCmpXchgInst;
class BasicBlock;
class CatchPadInst;
class CatchReturnInst;
+class CycleInfo;
class DominatorTree;
class FenceInst;
class LoopInfo;
@@ -175,6 +176,7 @@ class LLVM_ABI SimpleCaptureAnalysis final : public CaptureAnalysis {
class LLVM_ABI EarliestEscapeAnalysis final : public CaptureAnalysis {
DominatorTree &DT;
const LoopInfo *LI;
+ const CycleInfo *CI;
/// Map from identified local object to an instruction before which it does
/// not escape (or nullptr if it never escapes) and the possible components
@@ -189,8 +191,9 @@ class LLVM_ABI EarliestEscapeAnalysis final : public CaptureAnalysis {
DenseMap<Instruction *, TinyPtrVector<const Value *>> Inst2Obj;
public:
- EarliestEscapeAnalysis(DominatorTree &DT, const LoopInfo *LI = nullptr)
- : DT(DT), LI(LI) {}
+ EarliestEscapeAnalysis(DominatorTree &DT, const LoopInfo *LI = nullptr,
+ const CycleInfo *CI = nullptr)
+ : DT(DT), LI(LI), CI(CI) {}
CaptureComponents getCapturesBefore(const Value *Object, const Instruction *I,
bool OrAt) override;
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 80b14646c8889..dee305a6f40d2 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -31,6 +31,7 @@
#include "llvm/IR/Constant.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
+#include "llvm/IR/CycleInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
@@ -215,7 +216,10 @@ CaptureComponents SimpleCaptureAnalysis::getCapturesBefore(const Value *Object,
}
static bool isNotInCycle(const Instruction *I, const DominatorTree *DT,
- const LoopInfo *LI) {
+ const LoopInfo *LI, const CycleInfo *CI) {
+ if (CI)
+ return !CI->getCycle(I->getParent());
+
BasicBlock *BB = const_cast<BasicBlock *>(I->getParent());
SmallVector<BasicBlock *> Succs(successors(BB));
return Succs.empty() ||
@@ -252,10 +256,10 @@ EarliestEscapeAnalysis::getCapturesBefore(const Value *Object,
if (I == CaptureInst) {
if (OrAt)
return false;
- return isNotInCycle(I, &DT, LI);
+ return isNotInCycle(I, &DT, LI, CI);
}
- return !isPotentiallyReachable(CaptureInst, I, nullptr, &DT, LI);
+ return !isPotentiallyReachable(CaptureInst, I, nullptr, &DT, LI, CI);
};
if (IsNotCapturedBefore())
return CaptureComponents::None;
@@ -1910,7 +1914,7 @@ bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V,
if (!Inst || Inst->getParent()->isEntryBlock())
return true;
- return isNotInCycle(Inst, getDT(AAQI), /*LI*/ nullptr);
+ return isNotInCycle(Inst, getDT(AAQI), /*LI=*/nullptr, /*CI=*/nullptr);
}
/// Computes the symbolic difference between two de-composed GEPs.
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 2714074dddafc..28ecd3d33a384 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -40,9 +40,9 @@
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/CycleAnalysis.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/Loads.h"
-#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/MemorySSA.h"
@@ -951,11 +951,7 @@ struct DSEState {
PostDominatorTree &PDT;
const TargetLibraryInfo &TLI;
const DataLayout &DL;
- const LoopInfo &LI;
-
- // Whether the function contains any irreducible control flow, useful for
- // being accurately able to detect loops.
- bool ContainsIrreducibleLoops;
+ const CycleInfo &CI;
// All MemoryDefs that potentially could kill other MemDefs.
SmallVector<MemoryDef *, 64> MemDefs;
@@ -992,7 +988,7 @@ struct DSEState {
// Class contains self-reference, make sure it's not copied/moved.
DSEState(Function &F, AliasAnalysis &AA, MemorySSA &MSSA, DominatorTree &DT,
PostDominatorTree &PDT, const TargetLibraryInfo &TLI,
- const LoopInfo &LI);
+ const CycleInfo &CI);
DSEState(const DSEState &) = delete;
DSEState &operator=(const DSEState &) = delete;
@@ -1168,9 +1164,9 @@ static bool isFuncLocalAndNotCaptured(Value *Arg, const CallBase *CB,
DSEState::DSEState(Function &F, AliasAnalysis &AA, MemorySSA &MSSA,
DominatorTree &DT, PostDominatorTree &PDT,
- const TargetLibraryInfo &TLI, const LoopInfo &LI)
- : F(F), AA(AA), EA(DT, &LI), BatchAA(AA, &EA), MSSA(MSSA), DT(DT), PDT(PDT),
- TLI(TLI), DL(F.getDataLayout()), LI(LI) {
+ const TargetLibraryInfo &TLI, const CycleInfo &CI)
+ : F(F), AA(AA), EA(DT, nullptr, &CI), BatchAA(AA, &EA), MSSA(MSSA), DT(DT),
+ PDT(PDT), TLI(TLI), DL(F.getDataLayout()), CI(CI) {
// Collect blocks with throwing instructions not modeled in MemorySSA and
// alloc-like objects.
unsigned PO = 0;
@@ -1207,9 +1203,6 @@ DSEState::DSEState(Function &F, AliasAnalysis &AA, MemorySSA &MSSA,
InvisibleToCallerAfterRetBounded.insert({&AI, DeadBytes});
}
- // Collect whether there is any irreducible control flow in the function.
- ContainsIrreducibleLoops = mayContainIrreducibleControl(F, &LI);
-
AnyUnreachableExit = any_of(PDT.roots(), [](const BasicBlock *E) {
return isa<UnreachableInst>(E->getTerminator());
});
@@ -1605,9 +1598,8 @@ bool DSEState::isGuaranteedLoopIndependent(const Instruction *Current,
// would also be valid but we currently disable that to limit compile time).
if (Current->getParent() == KillingDef->getParent())
return true;
- const Loop *CurrentLI = LI.getLoopFor(Current->getParent());
- if (!ContainsIrreducibleLoops && CurrentLI &&
- CurrentLI == LI.getLoopFor(KillingDef->getParent()))
+ const Cycle *CurrentC = CI.getCycle(Current->getParent());
+ if (CurrentC && CurrentC == CI.getCycle(KillingDef->getParent()))
return true;
// Otherwise check the memory location is invariant to any loops.
return isGuaranteedLoopInvariant(CurrentLoc.Ptr);
@@ -1620,8 +1612,7 @@ bool DSEState::isGuaranteedLoopInvariant(const Value *Ptr) {
Ptr = GEP->getPointerOperand()->stripPointerCasts();
if (auto *I = dyn_cast<Instruction>(Ptr)) {
- return I->getParent()->isEntryBlock() ||
- (!ContainsIrreducibleLoops && !LI.getLoopFor(I->getParent()));
+ return I->getParent()->isEntryBlock() || !CI.getCycle(I->getParent());
}
return true;
}
@@ -2717,9 +2708,9 @@ bool DSEState::eliminateDeadDefs(const MemoryDefWrapper &KillingDefWrapper) {
static bool eliminateDeadStores(Function &F, AliasAnalysis &AA, MemorySSA &MSSA,
DominatorTree &DT, PostDominatorTree &PDT,
const TargetLibraryInfo &TLI,
- const LoopInfo &LI) {
+ const CycleInfo &CI) {
bool MadeChange = false;
- DSEState State(F, AA, MSSA, DT, PDT, TLI, LI);
+ DSEState State(F, AA, MSSA, DT, PDT, TLI, CI);
// For each store:
for (unsigned I = 0; I < State.MemDefs.size(); I++) {
MemoryDef *KillingDef = State.MemDefs[I];
@@ -2756,9 +2747,9 @@ PreservedAnalyses DSEPass::run(Function &F, FunctionAnalysisManager &AM) {
DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F);
MemorySSA &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
PostDominatorTree &PDT = AM.getResult<PostDominatorTreeAnalysis>(F);
- LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
+ CycleInfo &CI = AM.getResult<CycleAnalysis>(F);
- bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, LI);
+ bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, CI);
#ifdef LLVM_ENABLE_STATS
if (AreStatisticsEnabled())
@@ -2772,7 +2763,7 @@ PreservedAnalyses DSEPass::run(Function &F, FunctionAnalysisManager &AM) {
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
PA.preserve<MemorySSAAnalysis>();
- PA.preserve<LoopAnalysis>();
+ PA.preserve<CycleAnalysis>();
return PA;
}
@@ -2798,9 +2789,9 @@ class DSELegacyPass : public FunctionPass {
MemorySSA &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA();
PostDominatorTree &PDT =
getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
- LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ CycleInfo &CI = getAnalysis<CycleInfoWrapperPass>().getResult();
- bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, LI);
+ bool Changed = eliminateDeadStores(F, AA, MSSA, DT, PDT, TLI, CI);
#ifdef LLVM_ENABLE_STATS
if (AreStatisticsEnabled())
@@ -2822,8 +2813,8 @@ class DSELegacyPass : public FunctionPass {
AU.addRequired<MemorySSAWrapperPass>();
AU.addPreserved<PostDominatorTreeWrapperPass>();
AU.addPreserved<MemorySSAWrapperPass>();
- AU.addRequired<LoopInfoWrapperPass>();
- AU.addPreserved<LoopInfoWrapperPass>();
+ AU.addRequired<CycleInfoWrapperPass>();
+ AU.addPreserved<CycleInfoWrapperPass>();
AU.addRequired<AssumptionCacheTracker>();
}
};
diff --git a/llvm/test/Other/new-pm-defaults.ll b/llvm/test/Other/new-pm-defaults.ll
index f074b2fdd3ab8..240a3ef3ee539 100644
--- a/llvm/test/Other/new-pm-defaults.ll
+++ b/llvm/test/Other/new-pm-defaults.ll
@@ -217,6 +217,7 @@
; CHECK-O23SZ-NEXT: Running analysis: PostDominatorTreeAnalysis
; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
; CHECK-O23SZ-NEXT: Running pass: DSEPass
+; CHECK-O23SZ-NEXT: Running analysis: CycleAnalysis
; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
diff --git a/llvm/test/Other/new-pm-lto-defaults.ll b/llvm/test/Other/new-pm-lto-defaults.ll
index de0feca55e5b2..4eb4e4b4791c0 100644
--- a/llvm/test/Other/new-pm-lto-defaults.ll
+++ b/llvm/test/Other/new-pm-lto-defaults.ll
@@ -117,6 +117,7 @@
; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass on foo
; CHECK-O23SZ-NEXT: Running analysis: PostDominatorTreeAnalysis on foo
; CHECK-O23SZ-NEXT: Running pass: DSEPass on foo
+; CHECK-O23SZ-NEXT: Running analysis: CycleAnalysis
; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
; CHECK-O23SZ-NEXT: Running pass: MergedLoadStoreMotionPass on foo
; CHECK-EP-VECTORIZER-START-NEXT: Running pass: NoOpFunctionPass on foo
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
index b0d08316de4f0..0d9a96a304432 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-defaults.ll
@@ -142,6 +142,7 @@
; CHECK-O23SZ-NEXT: Running analysis: PostDominatorTreeAnalysis
; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
; CHECK-O23SZ-NEXT: Running pass: DSEPass
+; CHECK-O23SZ-NEXT: Running analysis: CycleAnalysis
; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
index 6b3e82a752899..703696b57135b 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-pgo-defaults.ll
@@ -126,6 +126,7 @@
; CHECK-O-NEXT: Running pass: ADCEPass
; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
; CHECK-O23SZ-NEXT: Running pass: DSEPass
+; CHECK-O23SZ-NEXT: Running analysis: CycleAnalysis
; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
diff --git a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
index 88dc18f605ce2..569ba647f16f2 100644
--- a/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-postlink-samplepgo-defaults.ll
@@ -135,6 +135,7 @@
; CHECK-O-NEXT: Running pass: ADCEPass
; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
; CHECK-O23SZ-NEXT: Running pass: DSEPass
+; CHECK-O23SZ-NEXT: Running analysis: CycleAnalysis
; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass
; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
index dd6acd2c51ee7..b146ae15eca58 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-defaults.ll
@@ -174,6 +174,7 @@
; CHECK-O23SZ-NEXT: Running analysis: PostDominatorTreeAnalysis
; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
; CHECK-O23SZ-NEXT: Running pass: DSEPass
+; CHECK-O23SZ-NEXT: Running analysis: CycleAnalysis
; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass
; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
index ee054527e20bd..b4a210ad9ab03 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-pgo-defaults.ll
@@ -175,6 +175,7 @@
; CHECK-O-NEXT: Running pass: ADCEPass
; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
; CHECK-O23SZ-NEXT: Running pass: DSEPass
+; CHECK-O23SZ-NEXT: Running analysis: CycleAnalysis
; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
diff --git a/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll b/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
index fd95e94f3c8b9..1efcb51fa61a6 100644
--- a/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
+++ b/llvm/test/Other/new-pm-thinlto-prelink-samplepgo-defaults.ll
@@ -139,6 +139,7 @@
; CHECK-O-NEXT: Running pass: ADCEPass
; CHECK-O23SZ-NEXT: Running pass: MemCpyOptPass
; CHECK-O23SZ-NEXT: Running pass: DSEPass
+; CHECK-O23SZ-NEXT: Running analysis: CycleAnalysis
; CHECK-O23SZ-NEXT: Running pass: MoveAutoInitPass on foo
; CHECK-O23SZ-NEXT: Running pass: LoopSimplifyPass
; CHECK-O23SZ-NEXT: Running pass: LCSSAPass
>From 33cb44669ce4b263595195cfd490e0a50caaf8f3 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Wed, 25 Mar 2026 15:22:44 +0100
Subject: [PATCH 2/2] Don't explicitly preserve CycleAnalysis
---
llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp | 1 -
1 file changed, 1 deletion(-)
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 28ecd3d33a384..75552f7af4bbf 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -2763,7 +2763,6 @@ PreservedAnalyses DSEPass::run(Function &F, FunctionAnalysisManager &AM) {
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
PA.preserve<MemorySSAAnalysis>();
- PA.preserve<CycleAnalysis>();
return PA;
}
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