[flang][HLFIR] Fix use-after-free when rewriting users in canonicalize

[kparzysz]

Rewriting an op can invalidate the operator range being iterated on. Store the users in a separate list, and iterate over the list instead.

This was detected by address sanitizer.

[llvmbot]

@llvm/pr-subscribers-flang-fir-hlfir

Author: Krzysztof Parzyszek (kparzysz)

Changes

Rewriting an op can invalidate the operator range being iterated on. Store the users in a separate list, and iterate over the list instead.

This was detected by address sanitizer.

---

Full diff: https://github.com/llvm/llvm-project/pull/84371.diff

1 Files Affected:

• (modified) flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp (+5-2)

diff --git a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
index 8bc92a991a69cf..74d94cd654b4a9 100644
--- a/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
+++ b/flang/lib/Optimizer/HLFIR/IR/HLFIROps.cpp
@@ -1152,7 +1152,9 @@ hlfir::MatmulOp::canonicalize(MatmulOp matmulOp,
 
       // but we do need to get rid of the hlfir.destroy for the hlfir.transpose
       // result (which is entirely removed)
-      for (mlir::Operation *user : transposeOp->getResult(0).getUsers())
+      llvm::SmallVector<mlir::Operation *> users(
+          transposeOp->getResult(0).getUsers());
+      for (mlir::Operation *user : users)
         if (auto destroyOp = mlir::dyn_cast_or_null<hlfir::DestroyOp>(user))
           rewriter.eraseOp(destroyOp);
       rewriter.eraseOp(transposeOp);
@@ -1864,7 +1866,8 @@ hlfir::ForallIndexOp::canonicalize(hlfir::ForallIndexOp indexOp,
       return mlir::failure();
 
   auto insertPt = rewriter.saveInsertionPoint();
-  for (mlir::Operation *user : indexOp->getResult(0).getUsers())
+  llvm::SmallVector<mlir::Operation*> users(indexOp->getResult(0).getUsers());
+  for (mlir::Operation *user : users)
     if (auto loadOp = mlir::dyn_cast<fir::LoadOp>(user)) {
       rewriter.setInsertionPoint(loadOp);
       rewriter.replaceOpWithNewOp<fir::ConvertOp>(

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[jeanPerier]

Thanks

[tblah]

LGTM, thanks!