[llvm] 2b3a410 - [DA] Check element size when analyzing deps between same instruction (#148813)

[via llvm-commits]

Author: Ryotaro Kasuga
Date: 2025-07-17T21:11:37+09:00
New Revision: 2b3a410f5bc8358a9e8594331d70c9c5d59633d8

URL: https://github.com/llvm/llvm-project/commit/2b3a410f5bc8358a9e8594331d70c9c5d59633d8
DIFF: https://github.com/llvm/llvm-project/commit/2b3a410f5bc8358a9e8594331d70c9c5d59633d8.diff

LOG: [DA] Check element size when analyzing deps between same instruction (#148813)

DependenceAnalysis checks whether the given addresses are divisible by
the element size of corresponding load/store instructions. However, this
check was only executed when the two instructions (Src and Dst) are
different. We must also perform the same check when Src and Dst are the
same instruction.

Fix the test added in #147715.

Added: 
    

Modified: 
    llvm/lib/Analysis/DependenceAnalysis.cpp
    llvm/test/Analysis/DependenceAnalysis/DifferentOffsets.ll
    llvm/test/Analysis/DependenceAnalysis/MIVCheckConst.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 428342f51ad2e..dd9a44b9aecac 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -3670,14 +3670,12 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
   const SCEV *SrcEv = SE->getMinusSCEV(SrcSCEV, SrcBase);
   const SCEV *DstEv = SE->getMinusSCEV(DstSCEV, DstBase);
 
-  if (Src != Dst) {
-    // Check that memory access offsets are multiples of element sizes.
-    if (!SE->isKnownMultipleOf(SrcEv, EltSize, Assume) ||
-        !SE->isKnownMultipleOf(DstEv, EltSize, Assume)) {
-      LLVM_DEBUG(dbgs() << "can't analyze SCEV with 
diff erent offsets\n");
-      return std::make_unique<Dependence>(Src, Dst,
-                                          SCEVUnionPredicate(Assume, *SE));
-    }
+  // Check that memory access offsets are multiples of element sizes.
+  if (!SE->isKnownMultipleOf(SrcEv, EltSize, Assume) ||
+      !SE->isKnownMultipleOf(DstEv, EltSize, Assume)) {
+    LLVM_DEBUG(dbgs() << "can't analyze SCEV with 
diff erent offsets\n");
+    return std::make_unique<Dependence>(Src, Dst,
+                                        SCEVUnionPredicate(Assume, *SE));
   }
 
   if (!Assume.empty()) {

diff  --git a/llvm/test/Analysis/DependenceAnalysis/DifferentOffsets.ll b/llvm/test/Analysis/DependenceAnalysis/DifferentOffsets.ll
index 4f95da4f79c57..d9ccea55dd478 100644
--- a/llvm/test/Analysis/DependenceAnalysis/DifferentOffsets.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/DifferentOffsets.ll
@@ -11,7 +11,7 @@
 define i32 @alias_with_
diff erent_offsets(ptr nocapture %A) {
 ; CHECK-LABEL: 'alias_with_
diff erent_offsets'
 ; CHECK-NEXT:  Src: store i32 2, ptr %arrayidx, align 1 --> Dst: store i32 2, ptr %arrayidx, align 1
-; CHECK-NEXT:    da analyze - none!
+; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: store i32 2, ptr %arrayidx, align 1 --> Dst: %0 = load i32, ptr %A, align 1
 ; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: %0 = load i32, ptr %A, align 1 --> Dst: %0 = load i32, ptr %A, align 1
@@ -207,11 +207,11 @@ end:
 ;        *((long long *)idx) = 1;
 ;      }
 ;
-; FIXME: There are loop-carried dependencies across iterations in the store.
+; There are loop-carried dependencies across iterations in the store.
 define void @multidim_accesses2(ptr %A) {
 ; CHECK-LABEL: 'multidim_accesses2'
 ; CHECK-NEXT:  Src: store i64 1, ptr %idx, align 4 --> Dst: store i64 1, ptr %idx, align 4
-; CHECK-NEXT:    da analyze - none!
+; CHECK-NEXT:    da analyze - confused!
 ;
 entry:
   br label %for.i

diff  --git a/llvm/test/Analysis/DependenceAnalysis/MIVCheckConst.ll b/llvm/test/Analysis/DependenceAnalysis/MIVCheckConst.ll
index c1f8c85f2bf0e..b498d70648bad 100644
--- a/llvm/test/Analysis/DependenceAnalysis/MIVCheckConst.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/MIVCheckConst.ll
@@ -40,6 +40,9 @@ define void @test(ptr %A, ptr %B, i1 %arg, i32 %n, i32 %m) #0 align 2 {
 ; CHECK-NEXT:    da analyze - confused!
 ; CHECK-NEXT:  Src: %v27 = load <32 x i32>, ptr %v25, align 256 --> Dst: %v27 = load <32 x i32>, ptr %v25, align 256
 ; CHECK-NEXT:    da analyze - consistent input [0 S S]!
+; CHECK-NEXT:    Runtime Assumptions:
+; CHECK-NEXT:    Equal predicate: (zext i7 (4 * (trunc i32 %v1 to i7) * (1 + (trunc i32 %n to i7))) to i32) == 0
+; CHECK-NEXT:    Equal predicate: (8 * (zext i4 (trunc i32 %v1 to i4) to i32))<nuw><nsw> == 0
 ; CHECK-NEXT:  Src: %v27 = load <32 x i32>, ptr %v25, align 256 --> Dst: %v32 = load <32 x i32>, ptr %v30, align 128
 ; CHECK-NEXT:    da analyze - input [* S S|<]!
 ; CHECK-NEXT:    Runtime Assumptions: