[llvm] [FlattenCFG] Fix an Imprecise Usage of AA (PR #128117)

[via llvm-commits]

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@@ -357,8 +357,12 @@ bool FlattenCFGOpt::CompareIfRegionBlock(BasicBlock *Block1, BasicBlock *Block2,
       for (BasicBlock::iterator BI(PBI2), BE(PTI2); BI != BE; ++BI) {
         if (BI->mayReadFromMemory() || BI->mayWriteToMemory()) {
           // Check alias with Head2.
-          if (!AA || !AA->isNoAlias(&*iter1, &*BI))
-            return false;
+          if (AA) {
+            MemoryLocation Loc1 = MemoryLocation::get(&*iter1);
+            MemoryLocation Loc2 = MemoryLocation::get(&*BI);
+            if (!AA->isNoAlias(Loc1, Loc2))
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Chengjunp wrote:

Thank you for pointing this out. Instead of making modifications here, I choose to implement a new alias helper function that takes in two instructions. Could you please help me check whether that is the right way to use `getModRefInfo` check the alias between two instructions? Thanks!

https://github.com/llvm/llvm-project/pull/128117