[llvm] ab6677e - [LICM] Only set AA metadata on hoisted load if it executes. (#117204)

[via llvm-commits]

Author: Florian Hahn
Date: 2024-11-26T14:16:16Z
New Revision: ab6677e7d64b4612d6c92877cb1d529f922268d2

URL: https://github.com/llvm/llvm-project/commit/ab6677e7d64b4612d6c92877cb1d529f922268d2
DIFF: https://github.com/llvm/llvm-project/commit/ab6677e7d64b4612d6c92877cb1d529f922268d2.diff

LOG: [LICM] Only set AA metadata on hoisted load if it executes. (#117204)

https://github.com/llvm/llvm-project/pull/116220 clarified that
violations of aliasing metadata are UB.

Only set the AA metadata after hoisting a log, if it is guaranteed to
execute in the original loop.

PR: https://github.com/llvm/llvm-project/pull/117204

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/LICM.cpp
    llvm/test/Transforms/LICM/hoist-metadata.ll
    llvm/test/Transforms/LICM/hoisting-preheader-debugloc.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 94bfe44a847a37..3ade3202728931 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -2030,7 +2030,9 @@ bool llvm::promoteLoopAccessesToScalars(
 
   bool DereferenceableInPH = false;
   bool StoreIsGuanteedToExecute = false;
+  bool LoadIsGuaranteedToExecute = false;
   bool FoundLoadToPromote = false;
+
   // Goes from Unknown to either Safe or Unsafe, but can't switch between them.
   enum {
     StoreSafe,
@@ -2089,6 +2091,10 @@ bool llvm::promoteLoopAccessesToScalars(
 
         Align InstAlignment = Load->getAlign();
 
+        if (!LoadIsGuaranteedToExecute)
+          LoadIsGuaranteedToExecute =
+              SafetyInfo->isGuaranteedToExecute(*UI, DT, CurLoop);
+
         // Note that proving a load safe to speculate requires proving
         // sufficient alignment at the target location.  Proving it guaranteed
         // to execute does as well.  Thus we can increase our guaranteed
@@ -2233,8 +2239,9 @@ bool llvm::promoteLoopAccessesToScalars(
   SSAUpdater SSA(&NewPHIs);
   LoopPromoter Promoter(SomePtr, LoopUses, SSA, ExitBlocks, InsertPts,
                         MSSAInsertPts, PIC, MSSAU, *LI, DL, Alignment,
-                        SawUnorderedAtomic, AATags, *SafetyInfo,
-                        StoreSafety == StoreSafe);
+                        SawUnorderedAtomic,
+                        StoreIsGuanteedToExecute ? AATags : AAMDNodes(),
+                        *SafetyInfo, StoreSafety == StoreSafe);
 
   // Set up the preheader to have a definition of the value.  It is the live-out
   // value from the preheader that uses in the loop will use.
@@ -2247,7 +2254,7 @@ bool llvm::promoteLoopAccessesToScalars(
       PreheaderLoad->setOrdering(AtomicOrdering::Unordered);
     PreheaderLoad->setAlignment(Alignment);
     PreheaderLoad->setDebugLoc(DebugLoc());
-    if (AATags)
+    if (AATags && LoadIsGuaranteedToExecute)
       PreheaderLoad->setAAMetadata(AATags);
 
     MemoryAccess *PreheaderLoadMemoryAccess = MSSAU.createMemoryAccessInBB(

diff  --git a/llvm/test/Transforms/LICM/hoist-metadata.ll b/llvm/test/Transforms/LICM/hoist-metadata.ll
index 60b61944b33ae0..f25cb966a37fc7 100644
--- a/llvm/test/Transforms/LICM/hoist-metadata.ll
+++ b/llvm/test/Transforms/LICM/hoist-metadata.ll
@@ -77,7 +77,7 @@ define void @noalias_metadata_load_may_not_execute() {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[A:%.*]] = alloca i32, align 16
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[A]]
-; CHECK-NEXT:    [[GEP_PROMOTED:%.*]] = load i32, ptr [[GEP]], align 4, !tbaa [[TBAA3:![0-9]+]], !noalias [[META7:![0-9]+]]
+; CHECK-NEXT:    [[GEP_PROMOTED:%.*]] = load i32, ptr [[GEP]], align 4
 ; CHECK-NEXT:    br label [[LOOP_HEADER:%.*]]
 ; CHECK:       loop.header:
 ; CHECK-NEXT:    [[ADD1:%.*]] = phi i32 [ [[GEP_PROMOTED]], [[ENTRY:%.*]] ], [ [[ADD:%.*]], [[LOOP_LATCH:%.*]] ]
@@ -92,7 +92,7 @@ define void @noalias_metadata_load_may_not_execute() {
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP_HEADER]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[ADD2:%.*]] = phi i32 [ [[ADD]], [[LOOP_LATCH]] ], [ [[ADD1]], [[LOOP_HEADER]] ]
-; CHECK-NEXT:    store i32 [[ADD2]], ptr [[GEP]], align 4, !tbaa [[TBAA3]], !noalias [[META7]]
+; CHECK-NEXT:    store i32 [[ADD2]], ptr [[GEP]], align 4
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -132,11 +132,4 @@ exit:
 ; CHECK: [[RNG0]] = !{i32 0, i32 10}
 ; CHECK: [[META1]] = !{}
 ; CHECK: [[META2]] = !{i64 4}
-; CHECK: [[TBAA3]] = !{[[META4:![0-9]+]], [[META4]], i64 0}
-; CHECK: [[META4]] = !{!"short", [[META5:![0-9]+]], i64 0}
-; CHECK: [[META5]] = !{!"omnipotent char", [[META6:![0-9]+]], i64 0}
-; CHECK: [[META6]] = !{!"Simple C/C++ TBAA"}
-; CHECK: [[META7]] = !{[[META8:![0-9]+]]}
-; CHECK: [[META8]] = distinct !{[[META8]], [[META9:![0-9]+]]}
-; CHECK: [[META9]] = distinct !{[[META9]]}
 ;.

diff  --git a/llvm/test/Transforms/LICM/hoisting-preheader-debugloc.ll b/llvm/test/Transforms/LICM/hoisting-preheader-debugloc.ll
index 570f4230c1a90d..61f0eb19a9bd1b 100644
--- a/llvm/test/Transforms/LICM/hoisting-preheader-debugloc.ll
+++ b/llvm/test/Transforms/LICM/hoisting-preheader-debugloc.ll
@@ -1,6 +1,8 @@
 ; RUN: opt -passes=licm %s -S | FileCheck %s
 
-; CHECK: %arrayidx4.promoted = load i32, ptr %arrayidx4, align 4, !tbaa !{{[0-9]+$}}
+; CHECK: %arrayidx4.promoted = load i32, ptr %arrayidx4, align 4
+; CHECK-NOT: !dbg
+; CHECK: br label %for.body
 
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"