[llvm] [LAA] Strip findForkedPointer (NFC) (PR #140298)
Ramkumar Ramachandra via llvm-commits
llvm-commits at lists.llvm.org
Tue Sep 9 06:43:54 PDT 2025
https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/140298
>From d50151b89cbc9fc11ac4b3b2c84e8301129a09d4 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Thu, 4 Sep 2025 17:20:42 +0100
Subject: [PATCH 1/3] [LAA] Strip findForkedPointer (NFC)
Remove a level of indirection due to findForkedPointer, in an effort to
improve code.
---
llvm/lib/Analysis/LoopAccessAnalysis.cpp | 71 +++++++++++-------------
1 file changed, 32 insertions(+), 39 deletions(-)
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index cfddd9980c86b..30e96d83a107d 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1231,48 +1231,44 @@ static void findForkedSCEVs(
}
}
-static SmallVector<PointerIntPair<const SCEV *, 1, bool>>
-findForkedPointer(PredicatedScalarEvolution &PSE,
- const DenseMap<Value *, const SCEV *> &StridesMap, Value *Ptr,
- const Loop *L) {
- ScalarEvolution *SE = PSE.getSE();
- assert(SE->isSCEVable(Ptr->getType()) && "Value is not SCEVable!");
- SmallVector<PointerIntPair<const SCEV *, 1, bool>> Scevs;
- findForkedSCEVs(SE, L, Ptr, Scevs, MaxForkedSCEVDepth);
-
- // For now, we will only accept a forked pointer with two possible SCEVs
- // that are either SCEVAddRecExprs or loop invariant.
- if (Scevs.size() == 2 &&
- (isa<SCEVAddRecExpr>(get<0>(Scevs[0])) ||
- SE->isLoopInvariant(get<0>(Scevs[0]), L)) &&
- (isa<SCEVAddRecExpr>(get<0>(Scevs[1])) ||
- SE->isLoopInvariant(get<0>(Scevs[1]), L))) {
- LLVM_DEBUG(dbgs() << "LAA: Found forked pointer: " << *Ptr << "\n");
- LLVM_DEBUG(dbgs() << "\t(1) " << *get<0>(Scevs[0]) << "\n");
- LLVM_DEBUG(dbgs() << "\t(2) " << *get<0>(Scevs[1]) << "\n");
- return Scevs;
- }
-
- return {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}};
-}
-
bool AccessAnalysis::createCheckForAccess(
RuntimePointerChecking &RtCheck, MemAccessInfo Access, Type *AccessTy,
const DenseMap<Value *, const SCEV *> &StridesMap,
DenseMap<Value *, unsigned> &DepSetId, Loop *TheLoop,
unsigned &RunningDepId, unsigned ASId, bool Assume) {
Value *Ptr = Access.getPointer();
+ ScalarEvolution *SE = PSE.getSE();
+ assert(SE->isSCEVable(Ptr->getType()) && "Value is not SCEVable!");
+
+ SmallVector<PointerIntPair<const SCEV *, 1, bool>> RTCheckPtrs;
+ findForkedSCEVs(SE, TheLoop, Ptr, RTCheckPtrs, MaxForkedSCEVDepth);
+ assert(!RTCheckPtrs.empty() &&
+ "Must have some runtime-check pointer candidates");
- SmallVector<PointerIntPair<const SCEV *, 1, bool>> TranslatedPtrs =
- findForkedPointer(PSE, StridesMap, Ptr, TheLoop);
- assert(!TranslatedPtrs.empty() && "must have some translated pointers");
+ auto IsLoopInvariantOrAR =
+ [&SE, &TheLoop](const PointerIntPair<const SCEV *, 1, bool> &P) {
+ return SE->isLoopInvariant(get<0>(P), TheLoop) ||
+ isa<SCEVAddRecExpr>(get<0>(P));
+ };
+
+ // RTCheckPtrs must have size 2 if there are forked pointers. Otherwise, there
+ // are no forked pointers; replaceSymbolicStridesSCEV in this case.
+ if (RTCheckPtrs.size() == 2 && all_of(RTCheckPtrs, IsLoopInvariantOrAR)) {
+ LLVM_DEBUG(dbgs() << "LAA: Found forked pointer: " << *Ptr << "\n");
+ for (auto [Idx, Q] : enumerate(RTCheckPtrs))
+ LLVM_DEBUG(dbgs() << "\t(" << Idx << ") " << *Q.getPointer() << "\n");
+ } else {
+ RTCheckPtrs.truncate(1);
+ RTCheckPtrs.front().setPointer(
+ replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr));
+ RTCheckPtrs.front().setInt(false);
+ }
/// Check whether all pointers can participate in a runtime bounds check. They
- /// must either be invariant or AddRecs. If ShouldCheckWrap is true, they also
- /// must not wrap.
- for (auto &P : TranslatedPtrs) {
+ /// must either be invariant or non-wrapping affine AddRecs.
+ for (auto &P : RTCheckPtrs) {
// The bounds for loop-invariant pointer is trivial.
- if (PSE.getSE()->isLoopInvariant(P.getPointer(), TheLoop))
+ if (SE->isLoopInvariant(P.getPointer(), TheLoop))
continue;
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(P.getPointer());
@@ -1283,21 +1279,18 @@ bool AccessAnalysis::createCheckForAccess(
// If there's only one option for Ptr, look it up after bounds and wrap
// checking, because assumptions might have been added to PSE.
- if (TranslatedPtrs.size() == 1) {
+ if (RTCheckPtrs.size() == 1) {
AR =
cast<SCEVAddRecExpr>(replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr));
P.setPointer(AR);
}
- // When we run after a failing dependency check we have to make sure
- // we don't have wrapping pointers.
- if (!isNoWrap(PSE, AR, TranslatedPtrs.size() == 1 ? Ptr : nullptr, AccessTy,
- TheLoop, Assume)) {
+ if (!isNoWrap(PSE, AR, RTCheckPtrs.size() == 1 ? Ptr : nullptr, AccessTy,
+ TheLoop, Assume))
return false;
- }
}
- for (auto [PtrExpr, NeedsFreeze] : TranslatedPtrs) {
+ for (const auto &[PtrExpr, NeedsFreeze] : RTCheckPtrs) {
// The id of the dependence set.
unsigned DepId;
>From bc4fc4ef6c678e62964f8faba45a4e0b6f9585da Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Fri, 5 Sep 2025 10:13:58 +0100
Subject: [PATCH 2/3] [LAA] Address review
---
llvm/lib/Analysis/LoopAccessAnalysis.cpp | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 30e96d83a107d..da8a15e839a53 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1245,23 +1245,19 @@ bool AccessAnalysis::createCheckForAccess(
assert(!RTCheckPtrs.empty() &&
"Must have some runtime-check pointer candidates");
+ // RTCheckPtrs must have size 2 if there are forked pointers. Otherwise, there
+ // are no forked pointers; replaceSymbolicStridesSCEV in this case.
auto IsLoopInvariantOrAR =
[&SE, &TheLoop](const PointerIntPair<const SCEV *, 1, bool> &P) {
return SE->isLoopInvariant(get<0>(P), TheLoop) ||
isa<SCEVAddRecExpr>(get<0>(P));
};
-
- // RTCheckPtrs must have size 2 if there are forked pointers. Otherwise, there
- // are no forked pointers; replaceSymbolicStridesSCEV in this case.
if (RTCheckPtrs.size() == 2 && all_of(RTCheckPtrs, IsLoopInvariantOrAR)) {
LLVM_DEBUG(dbgs() << "LAA: Found forked pointer: " << *Ptr << "\n");
for (auto [Idx, Q] : enumerate(RTCheckPtrs))
LLVM_DEBUG(dbgs() << "\t(" << Idx << ") " << *Q.getPointer() << "\n");
} else {
- RTCheckPtrs.truncate(1);
- RTCheckPtrs.front().setPointer(
- replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr));
- RTCheckPtrs.front().setInt(false);
+ RTCheckPtrs = {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}};
}
/// Check whether all pointers can participate in a runtime bounds check. They
>From dc1e6dffde265b877d59e40158756c40eb711ae9 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Tue, 9 Sep 2025 14:31:58 +0100
Subject: [PATCH 3/3] [LAA] Fix some nits
---
llvm/lib/Analysis/LoopAccessAnalysis.cpp | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index da8a15e839a53..87fae92977cd2 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1249,13 +1249,13 @@ bool AccessAnalysis::createCheckForAccess(
// are no forked pointers; replaceSymbolicStridesSCEV in this case.
auto IsLoopInvariantOrAR =
[&SE, &TheLoop](const PointerIntPair<const SCEV *, 1, bool> &P) {
- return SE->isLoopInvariant(get<0>(P), TheLoop) ||
- isa<SCEVAddRecExpr>(get<0>(P));
+ return SE->isLoopInvariant(P.getPointer(), TheLoop) ||
+ isa<SCEVAddRecExpr>(P.getPointer());
};
if (RTCheckPtrs.size() == 2 && all_of(RTCheckPtrs, IsLoopInvariantOrAR)) {
- LLVM_DEBUG(dbgs() << "LAA: Found forked pointer: " << *Ptr << "\n");
- for (auto [Idx, Q] : enumerate(RTCheckPtrs))
- LLVM_DEBUG(dbgs() << "\t(" << Idx << ") " << *Q.getPointer() << "\n");
+ LLVM_DEBUG(dbgs() << "LAA: Found forked pointer: " << *Ptr << "\n";
+ for (const auto &[Idx, Q] : enumerate(RTCheckPtrs)) dbgs()
+ << "\t(" << Idx << ") " << *Q.getPointer() << "\n");
} else {
RTCheckPtrs = {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}};
}
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