[llvm-branch-commits] [llvm] [LAA] Support monotonic pointers in LoopAccessAnalysis (PR #140721)
Sergey Kachkov via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Fri Nov 7 03:58:30 PST 2025
https://github.com/skachkov-sc updated https://github.com/llvm/llvm-project/pull/140721
>From 64a329ce099a2db1e5404a461069a7ce6827f57b Mon Sep 17 00:00:00 2001
From: Sergey Kachkov <sergey.kachkov at syntacore.com>
Date: Thu, 23 Jan 2025 16:16:40 +0300
Subject: [PATCH 1/2] [LAA] Add pre-commit test
---
.../LoopAccessAnalysis/monotonic-pointers.ll | 86 +++++++++++++++++++
1 file changed, 86 insertions(+)
create mode 100644 llvm/test/Analysis/LoopAccessAnalysis/monotonic-pointers.ll
diff --git a/llvm/test/Analysis/LoopAccessAnalysis/monotonic-pointers.ll b/llvm/test/Analysis/LoopAccessAnalysis/monotonic-pointers.ll
new file mode 100644
index 0000000000000..b13d79acc5ee4
--- /dev/null
+++ b/llvm/test/Analysis/LoopAccessAnalysis/monotonic-pointers.ll
@@ -0,0 +1,86 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -disable-output -passes='print<access-info>' %s 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+
+define void @monotonic_ptr_simple(ptr writeonly %dst, ptr readonly %src, i32 %c, i32 %n) {
+; CHECK-LABEL: 'monotonic_ptr_simple'
+; CHECK-NEXT: for.body:
+; CHECK-NEXT: Report: cannot identify array bounds
+; CHECK-NEXT: Dependences:
+; CHECK-NEXT: Run-time memory checks:
+; CHECK-NEXT: Grouped accesses:
+; CHECK-EMPTY:
+; CHECK-NEXT: Non vectorizable stores to invariant address were not found in loop.
+; CHECK-NEXT: SCEV assumptions:
+; CHECK-EMPTY:
+; CHECK-NEXT: Expressions re-written:
+;
+entry:
+ %wide.trip.count = zext nneg i32 %n to i64
+ br label %for.body
+
+for.body:
+ %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.inc ]
+ %dst.addr.09 = phi ptr [ %dst, %entry ], [ %dst.addr.1, %for.inc ]
+ %arrayidx = getelementptr inbounds i32, ptr %src, i64 %indvars.iv
+ %0 = load i32, ptr %arrayidx, align 4
+ %cmp1 = icmp slt i32 %0, %c
+ br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:
+ %incdec.ptr = getelementptr inbounds i8, ptr %dst.addr.09, i64 4
+ store i32 %0, ptr %dst.addr.09, align 4
+ br label %for.inc
+
+for.inc:
+ %dst.addr.1 = phi ptr [ %incdec.ptr, %if.then ], [ %dst.addr.09, %for.body ]
+ %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+ %exitcond.not = icmp eq i64 %indvars.iv.next, %wide.trip.count
+ br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+ ret void
+}
+
+define void @monotonic_ptr_indexed(ptr writeonly %dst, ptr readonly %src, i32 %c, i32 %n) {
+; CHECK-LABEL: 'monotonic_ptr_indexed'
+; CHECK-NEXT: for.body:
+; CHECK-NEXT: Report: cannot identify array bounds
+; CHECK-NEXT: Dependences:
+; CHECK-NEXT: Run-time memory checks:
+; CHECK-NEXT: Grouped accesses:
+; CHECK-EMPTY:
+; CHECK-NEXT: Non vectorizable stores to invariant address were not found in loop.
+; CHECK-NEXT: SCEV assumptions:
+; CHECK-EMPTY:
+; CHECK-NEXT: Expressions re-written:
+;
+entry:
+ %wide.trip.count = zext nneg i32 %n to i64
+ br label %for.body
+
+for.body:
+ %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.inc ]
+ %idx.012 = phi i32 [ 0, %entry ], [ %idx.1, %for.inc ]
+ %arrayidx = getelementptr inbounds i32, ptr %src, i64 %indvars.iv
+ %0 = load i32, ptr %arrayidx, align 4
+ %cmp1 = icmp slt i32 %0, %c
+ br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:
+ %inc = add nsw i32 %idx.012, 1
+ %idxprom4 = sext i32 %idx.012 to i64
+ %arrayidx5 = getelementptr inbounds i32, ptr %dst, i64 %idxprom4
+ store i32 %0, ptr %arrayidx5, align 4
+ br label %for.inc
+
+for.inc:
+ %idx.1 = phi i32 [ %inc, %if.then ], [ %idx.012, %for.body ]
+ %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+ %exitcond.not = icmp eq i64 %indvars.iv.next, %wide.trip.count
+ br i1 %exitcond.not, label %exit, label %for.body
+
+exit:
+ ret void
+}
>From 18aa00f7770f0ad79faa649232af57a5c06e407d Mon Sep 17 00:00:00 2001
From: Sergey Kachkov <sergey.kachkov at syntacore.com>
Date: Wed, 29 Jan 2025 15:28:42 +0300
Subject: [PATCH 2/2] [LAA] Support monotonic pointers in LoopAccessAnalysis
---
llvm/lib/Analysis/LoopAccessAnalysis.cpp | 23 +++++++++++++---
.../LoopAccessAnalysis/monotonic-pointers.ll | 26 +++++++++++++++++--
2 files changed, 43 insertions(+), 6 deletions(-)
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 5d88e5f54e3d6..4484c03f3b7c7 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -25,6 +25,7 @@
#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/AssumeBundleQueries.h"
#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/IVDescriptors.h"
#include "llvm/Analysis/LoopAnalysisManager.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopIterator.h"
@@ -1024,7 +1025,8 @@ static bool isNoWrap(PredicatedScalarEvolution &PSE, const SCEVAddRecExpr *AR,
if (AR->getNoWrapFlags(SCEV::NoWrapMask))
return true;
- if (Ptr && PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW))
+ if (Ptr && isa<SCEVAddRecExpr>(PSE.getSCEV(Ptr)) &&
+ PSE.hasNoOverflow(Ptr, SCEVWrapPredicate::IncrementNUSW))
return true;
// An nusw getelementptr that is an AddRec cannot wrap. If it would wrap,
@@ -1256,6 +1258,20 @@ static void findForkedSCEVs(
}
}
+// Conservatively replace SCEV of Ptr value if it can't be computed directly,
+// e.g. for monotonic values (they can be treated as affine AddRecs that are
+// updated under some predicate).
+static const SCEV *
+replacePtrSCEV(PredicatedScalarEvolution &PSE, Value *Ptr,
+ const DenseMap<Value *, const SCEV *> &StridesMap,
+ const Loop *L) {
+ ScalarEvolution *SE = PSE.getSE();
+ if (MonotonicDescriptor MD;
+ MonotonicDescriptor::isMonotonicVal(Ptr, L, MD, *SE))
+ return MD.getExpr();
+ return replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr);
+}
+
bool AccessAnalysis::createCheckForAccess(
RuntimePointerChecking &RtCheck, MemAccessInfo Access, Type *AccessTy,
const DenseMap<Value *, const SCEV *> &StridesMap,
@@ -1282,7 +1298,7 @@ bool AccessAnalysis::createCheckForAccess(
for (const auto &[Idx, Q] : enumerate(RTCheckPtrs)) dbgs()
<< "\t(" << Idx << ") " << *Q.getPointer() << "\n");
} else {
- RTCheckPtrs = {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}};
+ RTCheckPtrs = {{replacePtrSCEV(PSE, Ptr, StridesMap, TheLoop), false}};
}
/// Check whether all pointers can participate in a runtime bounds check. They
@@ -1301,8 +1317,7 @@ 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 (RTCheckPtrs.size() == 1) {
- AR =
- cast<SCEVAddRecExpr>(replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr));
+ AR = cast<SCEVAddRecExpr>(replacePtrSCEV(PSE, Ptr, StridesMap, TheLoop));
P.setPointer(AR);
}
diff --git a/llvm/test/Analysis/LoopAccessAnalysis/monotonic-pointers.ll b/llvm/test/Analysis/LoopAccessAnalysis/monotonic-pointers.ll
index b13d79acc5ee4..6c91a4e332573 100644
--- a/llvm/test/Analysis/LoopAccessAnalysis/monotonic-pointers.ll
+++ b/llvm/test/Analysis/LoopAccessAnalysis/monotonic-pointers.ll
@@ -6,10 +6,21 @@ target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
define void @monotonic_ptr_simple(ptr writeonly %dst, ptr readonly %src, i32 %c, i32 %n) {
; CHECK-LABEL: 'monotonic_ptr_simple'
; CHECK-NEXT: for.body:
-; CHECK-NEXT: Report: cannot identify array bounds
+; CHECK-NEXT: Memory dependences are safe with run-time checks
; CHECK-NEXT: Dependences:
; CHECK-NEXT: Run-time memory checks:
+; CHECK-NEXT: Check 0:
+; CHECK-NEXT: Comparing group GRP0:
+; CHECK-NEXT: %dst.addr.09 = phi ptr [ %dst, %entry ], [ %dst.addr.1, %for.inc ]
+; CHECK-NEXT: Against group GRP1:
+; CHECK-NEXT: %arrayidx = getelementptr inbounds i32, ptr %src, i64 %indvars.iv
; CHECK-NEXT: Grouped accesses:
+; CHECK-NEXT: Group GRP0:
+; CHECK-NEXT: (Low: %dst High: ((4 * (zext i32 %n to i64))<nuw><nsw> + %dst))
+; CHECK-NEXT: Member: {%dst,+,4}<nsw><%for.body>
+; CHECK-NEXT: Group GRP1:
+; CHECK-NEXT: (Low: %src High: ((4 * (zext i32 %n to i64))<nuw><nsw> + %src))
+; CHECK-NEXT: Member: {%src,+,4}<nuw><%for.body>
; CHECK-EMPTY:
; CHECK-NEXT: Non vectorizable stores to invariant address were not found in loop.
; CHECK-NEXT: SCEV assumptions:
@@ -46,10 +57,21 @@ exit:
define void @monotonic_ptr_indexed(ptr writeonly %dst, ptr readonly %src, i32 %c, i32 %n) {
; CHECK-LABEL: 'monotonic_ptr_indexed'
; CHECK-NEXT: for.body:
-; CHECK-NEXT: Report: cannot identify array bounds
+; CHECK-NEXT: Memory dependences are safe with run-time checks
; CHECK-NEXT: Dependences:
; CHECK-NEXT: Run-time memory checks:
+; CHECK-NEXT: Check 0:
+; CHECK-NEXT: Comparing group GRP0:
+; CHECK-NEXT: %arrayidx5 = getelementptr inbounds i32, ptr %dst, i64 %idxprom4
+; CHECK-NEXT: Against group GRP1:
+; CHECK-NEXT: %arrayidx = getelementptr inbounds i32, ptr %src, i64 %indvars.iv
; CHECK-NEXT: Grouped accesses:
+; CHECK-NEXT: Group GRP0:
+; CHECK-NEXT: (Low: %dst High: ((4 * (zext i32 %n to i64))<nuw><nsw> + %dst))
+; CHECK-NEXT: Member: {%dst,+,4}<%for.body>
+; CHECK-NEXT: Group GRP1:
+; CHECK-NEXT: (Low: %src High: ((4 * (zext i32 %n to i64))<nuw><nsw> + %src))
+; CHECK-NEXT: Member: {%src,+,4}<nuw><%for.body>
; CHECK-EMPTY:
; CHECK-NEXT: Non vectorizable stores to invariant address were not found in loop.
; CHECK-NEXT: SCEV assumptions:
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