[llvm] dec4cfd - [LAA] Use loop guards when checking invariant accesses.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2024-10-04T12:23:13+01:00
New Revision: dec4cfdb09596f34f17a653ad405ab2551b09039

URL: https://github.com/llvm/llvm-project/commit/dec4cfdb09596f34f17a653ad405ab2551b09039
DIFF: https://github.com/llvm/llvm-project/commit/dec4cfdb09596f34f17a653ad405ab2551b09039.diff

LOG: [LAA] Use loop guards when checking invariant accesses.

Apply loop guards to start and end pointers like done in other places to
improve results.

Added: 
    

Modified: 
    llvm/lib/Analysis/LoopAccessAnalysis.cpp
    llvm/test/Analysis/LoopAccessAnalysis/no-dep-via-loop-guards.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 3f189724763d47..fe00ea0097a43a 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1943,16 +1943,24 @@ MemoryDepChecker::getDependenceDistanceStrideAndSize(
   // required for correctness.
   if (SE.isLoopInvariant(Src, InnermostLoop) ||
       SE.isLoopInvariant(Sink, InnermostLoop)) {
-    const auto &[SrcStart, SrcEnd] =
+    const auto &[SrcStart_, SrcEnd_] =
         getStartAndEndForAccess(InnermostLoop, Src, ATy, PSE, PointerBounds);
-    const auto &[SinkStart, SinkEnd] =
+    const auto &[SinkStart_, SinkEnd_] =
         getStartAndEndForAccess(InnermostLoop, Sink, BTy, PSE, PointerBounds);
-    if (!isa<SCEVCouldNotCompute>(SrcStart) &&
-        !isa<SCEVCouldNotCompute>(SrcEnd) &&
-        !isa<SCEVCouldNotCompute>(SinkStart) &&
-        !isa<SCEVCouldNotCompute>(SinkEnd)) {
+    if (!isa<SCEVCouldNotCompute>(SrcStart_) &&
+        !isa<SCEVCouldNotCompute>(SrcEnd_) &&
+        !isa<SCEVCouldNotCompute>(SinkStart_) &&
+        !isa<SCEVCouldNotCompute>(SinkEnd_)) {
+      if (!LoopGuards)
+        LoopGuards.emplace(
+            ScalarEvolution::LoopGuards::collect(InnermostLoop, SE));
+      auto SrcEnd = SE.applyLoopGuards(SrcEnd_, *LoopGuards);
+      auto SinkStart = SE.applyLoopGuards(SinkStart_, *LoopGuards);
       if (SE.isKnownPredicate(CmpInst::ICMP_ULE, SrcEnd, SinkStart))
         return MemoryDepChecker::Dependence::NoDep;
+
+      auto SinkEnd = SE.applyLoopGuards(SinkEnd_, *LoopGuards);
+      auto SrcStart = SE.applyLoopGuards(SrcStart_, *LoopGuards);
       if (SE.isKnownPredicate(CmpInst::ICMP_ULE, SinkEnd, SrcStart))
         return MemoryDepChecker::Dependence::NoDep;
     }

diff  --git a/llvm/test/Analysis/LoopAccessAnalysis/no-dep-via-loop-guards.ll b/llvm/test/Analysis/LoopAccessAnalysis/no-dep-via-loop-guards.ll
index 5ff8eb59cfbf19..2cb98b1a81993b 100644
--- a/llvm/test/Analysis/LoopAccessAnalysis/no-dep-via-loop-guards.ll
+++ b/llvm/test/Analysis/LoopAccessAnalysis/no-dep-via-loop-guards.ll
@@ -2,17 +2,11 @@
 ; RUN: opt -passes='print<access-info>' -disable-output < %s  2>&1 | FileCheck %s
 
 ; Loop guard for %off guarantees the accesses in the loop do not overlap.
-; TODO: currently missed by LAA
 define void @access_after_via_loop_guard(ptr %a, i64 %off) {
 ; CHECK-LABEL: 'access_after_via_loop_guard'
 ; CHECK-NEXT:    loop:
-; CHECK-NEXT:      Report: unsafe dependent memory operations in loop. Use #pragma clang loop distribute(enable) to allow loop distribution to attempt to isolate the offending operations into a separate loop
-; CHECK-NEXT:  Unknown data dependence.
+; CHECK-NEXT:      Memory dependences are safe
 ; CHECK-NEXT:      Dependences:
-; CHECK-NEXT:        Unknown:
-; CHECK-NEXT:            %l = load i32, ptr %gep.after, align 4 ->
-; CHECK-NEXT:            store i32 %add, ptr %gep, align 4
-; CHECK-EMPTY:
 ; CHECK-NEXT:      Run-time memory checks:
 ; CHECK-NEXT:      Grouped accesses:
 ; CHECK-EMPTY:
@@ -203,17 +197,11 @@ exit:
 }
 
 ; Loop guard for %off guarantees the accesses in the loop do not overlap.
-; TODO: currently missed by LAA
 define void @access_after_via_loop_guard_eq_loop_cond(ptr %a, i64 %off) {
 ; CHECK-LABEL: 'access_after_via_loop_guard_eq_loop_cond'
 ; CHECK-NEXT:    loop:
-; CHECK-NEXT:      Report: unsafe dependent memory operations in loop. Use #pragma clang loop distribute(enable) to allow loop distribution to attempt to isolate the offending operations into a separate loop
-; CHECK-NEXT:  Unknown data dependence.
+; CHECK-NEXT:      Memory dependences are safe
 ; CHECK-NEXT:      Dependences:
-; CHECK-NEXT:        Unknown:
-; CHECK-NEXT:            %l = load i32, ptr %gep.after, align 4 ->
-; CHECK-NEXT:            store i32 %add, ptr %gep, align 4
-; CHECK-EMPTY:
 ; CHECK-NEXT:      Run-time memory checks:
 ; CHECK-NEXT:      Grouped accesses:
 ; CHECK-EMPTY: