[llvm] LAA: drop unnecessary args, clarifying APIs (PR #127479)
Ramkumar Ramachandra via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 17 06:29:14 PST 2025
https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/127479
>From f59af3b674416764ebb2f00379954cd69a3c548d Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Mon, 17 Feb 2025 11:38:55 +0000
Subject: [PATCH 1/2] LAA: drop unnecessary args, clarifying APIs
Drop unnecessary arguments in the APIs of getStrideFromAddRec and
isNoWrapAddRec, to clarify their usage. Additionally, free
isNoWrapAddRec from the AddRec check, and rename it to isNoWrapGEP.
---
llvm/lib/Analysis/LoopAccessAnalysis.cpp | 41 ++++++++++++------------
1 file changed, 20 insertions(+), 21 deletions(-)
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 7d6dbd51a404d..1e7685a426d69 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -793,14 +793,15 @@ class AccessAnalysis {
} // end anonymous namespace
-/// Try to compute the stride for \p AR. Used by getPtrStride.
+/// Try to compute a constant stride for \p AR. Used by getPtrStride and
+/// isNoWrap.
static std::optional<int64_t>
getStrideFromAddRec(const SCEVAddRecExpr *AR, const Loop *Lp, Type *AccessTy,
- Value *Ptr, PredicatedScalarEvolution &PSE) {
+ PredicatedScalarEvolution &PSE) {
// The access function must stride over the innermost loop.
if (Lp != AR->getLoop()) {
LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop "
- << *Ptr << " SCEV: " << *AR << "\n");
+ << "SCEV: " << *AR << "\n");
return std::nullopt;
}
@@ -810,8 +811,8 @@ getStrideFromAddRec(const SCEVAddRecExpr *AR, const Loop *Lp, Type *AccessTy,
// Calculate the pointer stride and check if it is constant.
const SCEVConstant *C = dyn_cast<SCEVConstant>(Step);
if (!C) {
- LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptr
- << " SCEV: " << *AR << "\n");
+ LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided "
+ << "SCEV: " << *AR << "\n");
return std::nullopt;
}
@@ -835,16 +836,21 @@ getStrideFromAddRec(const SCEVAddRecExpr *AR, const Loop *Lp, Type *AccessTy,
return Stride;
}
-static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR,
- PredicatedScalarEvolution &PSE, const Loop *L);
+static bool isNoWrapGEP(Value *Ptr, PredicatedScalarEvolution &PSE,
+ const Loop *L);
-/// Check whether a pointer address cannot wrap.
+/// Check whether \p AR is a non-wrapping AddRec, or if \p Ptr is a non-wrapping
+/// GEP.
static bool isNoWrap(PredicatedScalarEvolution &PSE, const SCEVAddRecExpr *AR,
Value *Ptr, Type *AccessTy, const Loop *L, bool Assume,
std::optional<int64_t> Stride = std::nullopt) {
+ // FIXME: This should probably only return true for NUW.
+ if (AR->getNoWrapFlags(SCEV::NoWrapMask))
+ return true;
+
// The address calculation must not wrap. Otherwise, a dependence could be
// inverted.
- if (isNoWrapAddRec(Ptr, AR, PSE, L))
+ if (isNoWrapGEP(Ptr, PSE, L))
return true;
// An nusw getelementptr that is an AddRec cannot wrap. If it would wrap,
@@ -857,7 +863,7 @@ static bool isNoWrap(PredicatedScalarEvolution &PSE, const SCEVAddRecExpr *AR,
return true;
if (!Stride)
- Stride = getStrideFromAddRec(AR, L, AccessTy, Ptr, PSE);
+ Stride = getStrideFromAddRec(AR, L, AccessTy, PSE);
if (Stride) {
// If the null pointer is undefined, then a access sequence which would
// otherwise access it can be assumed not to unsigned wrap. Note that this
@@ -1445,15 +1451,9 @@ void AccessAnalysis::processMemAccesses() {
}
}
-/// Return true if an AddRec pointer \p Ptr is unsigned non-wrapping,
-/// i.e. monotonically increasing/decreasing.
-static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR,
- PredicatedScalarEvolution &PSE, const Loop *L) {
-
- // FIXME: This should probably only return true for NUW.
- if (AR->getNoWrapFlags(SCEV::NoWrapMask))
- return true;
-
+/// Check whether \p Ptr is non-wrapping GEP.
+static bool isNoWrapGEP(Value *Ptr, PredicatedScalarEvolution &PSE,
+ const Loop *L) {
if (PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW))
return true;
@@ -1524,8 +1524,7 @@ llvm::getPtrStride(PredicatedScalarEvolution &PSE, Type *AccessTy, Value *Ptr,
return std::nullopt;
}
- std::optional<int64_t> Stride =
- getStrideFromAddRec(AR, Lp, AccessTy, Ptr, PSE);
+ std::optional<int64_t> Stride = getStrideFromAddRec(AR, Lp, AccessTy, PSE);
if (!ShouldCheckWrap || !Stride)
return Stride;
>From a579cedd7a716d2c7e2a5bee358606c94cc6e056 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Mon, 17 Feb 2025 14:25:00 +0000
Subject: [PATCH 2/2] LAA: address review
---
llvm/lib/Analysis/LoopAccessAnalysis.cpp | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 1e7685a426d69..23bfd9989469a 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -797,11 +797,11 @@ class AccessAnalysis {
/// isNoWrap.
static std::optional<int64_t>
getStrideFromAddRec(const SCEVAddRecExpr *AR, const Loop *Lp, Type *AccessTy,
- PredicatedScalarEvolution &PSE) {
+ Value *Ptr, PredicatedScalarEvolution &PSE) {
// The access function must stride over the innermost loop.
if (Lp != AR->getLoop()) {
LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop "
- << "SCEV: " << *AR << "\n");
+ << *Ptr << " SCEV: " << *AR << "\n");
return std::nullopt;
}
@@ -811,8 +811,8 @@ getStrideFromAddRec(const SCEVAddRecExpr *AR, const Loop *Lp, Type *AccessTy,
// Calculate the pointer stride and check if it is constant.
const SCEVConstant *C = dyn_cast<SCEVConstant>(Step);
if (!C) {
- LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided "
- << "SCEV: " << *AR << "\n");
+ LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptr
+ << " SCEV: " << *AR << "\n");
return std::nullopt;
}
@@ -848,6 +848,9 @@ static bool isNoWrap(PredicatedScalarEvolution &PSE, const SCEVAddRecExpr *AR,
if (AR->getNoWrapFlags(SCEV::NoWrapMask))
return true;
+ if (PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW))
+ return true;
+
// The address calculation must not wrap. Otherwise, a dependence could be
// inverted.
if (isNoWrapGEP(Ptr, PSE, L))
@@ -863,7 +866,7 @@ static bool isNoWrap(PredicatedScalarEvolution &PSE, const SCEVAddRecExpr *AR,
return true;
if (!Stride)
- Stride = getStrideFromAddRec(AR, L, AccessTy, PSE);
+ Stride = getStrideFromAddRec(AR, L, AccessTy, Ptr, PSE);
if (Stride) {
// If the null pointer is undefined, then a access sequence which would
// otherwise access it can be assumed not to unsigned wrap. Note that this
@@ -1454,9 +1457,6 @@ void AccessAnalysis::processMemAccesses() {
/// Check whether \p Ptr is non-wrapping GEP.
static bool isNoWrapGEP(Value *Ptr, PredicatedScalarEvolution &PSE,
const Loop *L) {
- if (PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW))
- return true;
-
// Scalar evolution does not propagate the non-wrapping flags to values that
// are derived from a non-wrapping induction variable because non-wrapping
// could be flow-sensitive.
@@ -1524,7 +1524,8 @@ llvm::getPtrStride(PredicatedScalarEvolution &PSE, Type *AccessTy, Value *Ptr,
return std::nullopt;
}
- std::optional<int64_t> Stride = getStrideFromAddRec(AR, Lp, AccessTy, PSE);
+ std::optional<int64_t> Stride =
+ getStrideFromAddRec(AR, Lp, AccessTy, Ptr, PSE);
if (!ShouldCheckWrap || !Stride)
return Stride;
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