[llvm-branch-commits] [llvm] [DA] Overflow check in WeakCrossing Delta calculaton (PR #185046)

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Ehsan Amiri (amehsan)

<details>
<summary>Changes</summary>

When subtracting the constant part of two addrecs, we need to ensure the calculation won't overflow. If it may overflow, we conservatively stop the analysis and return false.

---
Full diff: https://github.com/llvm/llvm-project/pull/185046.diff


3 Files Affected:

- (modified) llvm/lib/Analysis/DependenceAnalysis.cpp (+4-1) 
- (modified) llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll (+1-1) 
- (modified) llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-overflow.ll (+1-1) 


``````````diff
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 8f79457449b45..01d33f208aa2e 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -1383,7 +1383,10 @@ bool DependenceInfo::weakCrossingSIVtest(const SCEVAddRecExpr *Src,
   ++WeakCrossingSIVapplications;
   assert(0 < Level && Level <= CommonLevels && "Level out of range");
   Level--;
-  const SCEV *Delta = SE->getMinusSCEV(DstConst, SrcConst);
+  const SCEV *Delta = minusSCEVNoSignedOverflow(DstConst, SrcConst, *SE);
+  if (Delta == nullptr)
+    return false;
+
   LLVM_DEBUG(dbgs() << "\t    Delta = " << *Delta << "\n");
   if (Delta->isZero()) {
     Result.DV[Level].Direction &= ~Dependence::DVEntry::LT;
diff --git a/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll b/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll
index 406dfaf96cfb7..b4aa1d698d840 100644
--- a/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-large-btc.ll
@@ -29,7 +29,7 @@ define void @weak_crossing_siv_large_btc(ptr %A) {
 ; CHECK-WEAK-CROSSING-SIV-NEXT:  Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 0, ptr %gep.0, align 1
 ; CHECK-WEAK-CROSSING-SIV-NEXT:    da analyze - output [*]!
 ; CHECK-WEAK-CROSSING-SIV-NEXT:  Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 0, ptr %gep.1, align 1
-; CHECK-WEAK-CROSSING-SIV-NEXT:    da analyze - none!
+; CHECK-WEAK-CROSSING-SIV-NEXT:    da analyze - output [*|<]!
 ; CHECK-WEAK-CROSSING-SIV-NEXT:  Src: store i8 0, ptr %gep.1, align 1 --> Dst: store i8 0, ptr %gep.1, align 1
 ; CHECK-WEAK-CROSSING-SIV-NEXT:    da analyze - output [*]!
 ;
diff --git a/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-overflow.ll b/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-overflow.ll
index acc1c0a69eb0f..9564fbb7b26ce 100644
--- a/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-overflow.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/weak-crossing-siv-overflow.ll
@@ -35,7 +35,7 @@ define void @weakcorssing_delta_ovfl(ptr %A) {
 ; CHECK-WEAK-CROSSING-SIV-NEXT:  Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 0, ptr %idx.0, align 1
 ; CHECK-WEAK-CROSSING-SIV-NEXT:    da analyze - output [*]!
 ; CHECK-WEAK-CROSSING-SIV-NEXT:  Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 1, ptr %idx.1, align 1
-; CHECK-WEAK-CROSSING-SIV-NEXT:    da analyze - none!
+; CHECK-WEAK-CROSSING-SIV-NEXT:    da analyze - output [*|<]!
 ; CHECK-WEAK-CROSSING-SIV-NEXT:  Src: store i8 1, ptr %idx.1, align 1 --> Dst: store i8 1, ptr %idx.1, align 1
 ; CHECK-WEAK-CROSSING-SIV-NEXT:    da analyze - output [*]!
 ;

``````````

</details>


https://github.com/llvm/llvm-project/pull/185046