[llvm] [LAA]Fix implicit trunc from int64 to int and losing info (PR #139553)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Alexey Bataev (alexey-bataev)

<details>
<summary>Changes</summary>

Need to check if the distance fits into int size before trying to get
int64_t difference and store it in int.

Fixes #<!-- -->139202


---
Full diff: https://github.com/llvm/llvm-project/pull/139553.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/LoopAccessAnalysis.cpp (+4) 
- (modified) llvm/test/Transforms/SLPVectorizer/X86/long-pointer-distance.ll (+7-1) 


``````````diff
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index f4e1d632b4d7d..f5f012e4744ea 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1585,6 +1585,8 @@ std::optional<int> llvm::getPointersDiff(Type *ElemTyA, Value *PtrA,
     OffsetB = OffsetB.sextOrTrunc(IdxWidth);
 
     OffsetB -= OffsetA;
+    if (OffsetB.getSignificantBits() > sizeof(int) * 8)
+      return std::nullopt;
     Val = OffsetB.getSExtValue();
   } else {
     // Otherwise compute the distance with SCEV between the base pointers.
@@ -1594,6 +1596,8 @@ std::optional<int> llvm::getPointersDiff(Type *ElemTyA, Value *PtrA,
         SE.computeConstantDifference(PtrSCEVB, PtrSCEVA);
     if (!Diff)
       return std::nullopt;
+    if (Diff->getSignificantBits() > sizeof(int) * 8)
+      return std::nullopt;
     Val = Diff->getSExtValue();
   }
   int Size = DL.getTypeStoreSize(ElemTyA);
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/long-pointer-distance.ll b/llvm/test/Transforms/SLPVectorizer/X86/long-pointer-distance.ll
index 9cfafd2784488..f663d120b136a 100644
--- a/llvm/test/Transforms/SLPVectorizer/X86/long-pointer-distance.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/long-pointer-distance.ll
@@ -5,7 +5,13 @@ define void @test(ptr %this) {
 ; CHECK-LABEL: define void @test(
 ; CHECK-SAME: ptr [[THIS:%.*]]) #[[ATTR0:[0-9]+]] {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
-; CHECK-NEXT:    store <4 x i64> <i64 1, i64 2, i64 3, i64 4>, ptr [[THIS]], align 8
+; CHECK-NEXT:    store i64 1, ptr [[THIS]], align 8
+; CHECK-NEXT:    [[B:%.*]] = getelementptr i8, ptr [[THIS]], i64 8
+; CHECK-NEXT:    store i64 2, ptr [[B]], align 8
+; CHECK-NEXT:    [[C:%.*]] = getelementptr i8, ptr [[THIS]], i64 4294967312
+; CHECK-NEXT:    store i64 3, ptr [[C]], align 8
+; CHECK-NEXT:    [[D:%.*]] = getelementptr i8, ptr [[THIS]], i64 4294967320
+; CHECK-NEXT:    store i64 4, ptr [[D]], align 8
 ; CHECK-NEXT:    ret void
 ;
 entry:

``````````

</details>


https://github.com/llvm/llvm-project/pull/139553