[llvm-branch-commits] [llvm] [DA] Add overflow check in GCD MIV (PR #172003)

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Ryotaro Kasuga (kasuga-fj)

<details>
<summary>Changes</summary>

Add an overflow check in GCD MIV. Fix the test case added in #<!-- -->172002 .

---
Full diff: https://github.com/llvm/llvm-project/pull/172003.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/DependenceAnalysis.cpp (+3-1) 
- (modified) llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll (+2-3) 


``````````diff
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 9b9c80a9b3266..b5d1a325d6ffe 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -2653,7 +2653,9 @@ bool DependenceInfo::gcdMIVtest(const SCEV *Src, const SCEV *Dst,
         !accumulateCoefficientsGCD(Dst, CurLoop, DstCoeff, RunningGCD))
       return false;
 
-    Delta = SE->getMinusSCEV(SrcCoeff, DstCoeff);
+    Delta = minusSCEVNoSignedOverflow(DstCoeff, SrcCoeff, *SE);
+    if (!Delta)
+      continue;
     // If the coefficient is the product of a constant and other stuff,
     // we can use the constant in the GCD computation.
     std::optional<APInt> ConstCoeff = getConstantCoefficient(Delta);
diff --git a/llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll b/llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll
index 2b00856aa9a52..6496cb41e733b 100644
--- a/llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll
+++ b/llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll
@@ -190,8 +190,7 @@ exit:
 ;     if (offset1 == -5) A[offset1] = 0;
 ;   }
 ;
-; FIXME: DependenceAnalysis fails to detect dependency between two stores. Also
-; GCD MIV misses '='-dependency.
+; FIXME: DependenceAnalysis fails to detect dependency between two stores.
 ;
 ; memory accesses                     | (i,j) == (1844674407370955161,1) | (i,j) == (1844674407370955160,1)
 ; ------------------------------------|----------------------------------|----------------------------------
@@ -211,7 +210,7 @@ define void @gcdmiv_delta_ovfl2(ptr %A) {
 ; CHECK-GCD-MIV-NEXT:  Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 0, ptr %gep.0, align 1
 ; CHECK-GCD-MIV-NEXT:    da analyze - output [* *]!
 ; CHECK-GCD-MIV-NEXT:  Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 0, ptr %gep.1, align 1
-; CHECK-GCD-MIV-NEXT:    da analyze - output [* <>]!
+; CHECK-GCD-MIV-NEXT:    da analyze - output [* *|<]!
 ; CHECK-GCD-MIV-NEXT:  Src: store i8 0, ptr %gep.1, align 1 --> Dst: store i8 0, ptr %gep.1, align 1
 ; CHECK-GCD-MIV-NEXT:    da analyze - output [* *]!
 ;

``````````

</details>


https://github.com/llvm/llvm-project/pull/172003