[flang] fix Werror=dangling-reference

[sebpop]

when compiling with g++ 13.3.0 flang build fails with:

llvm-project/flang/lib/Semantics/expression.cpp:424:17: error: possibly dangling reference to a temporary [-Werror=dangling-reference]
424 | const Symbol &coarraySymbol{ref.GetBase().GetLastSymbol()};
| ^~~~~~~~~~~~~
llvm-project/flang/lib/Semantics/expression.cpp:424:58: note: the temporary was destroyed at the end of the full expression ‘Fortran::evaluate::CoarrayRef::GetBase() const().Fortran::evaluate::NamedEntity::GetLastSymbol()’
424 | const Symbol &coarraySymbol{ref.GetBase().GetLastSymbol()};
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~

Keep the base in a temporary variable to make sure it is not deleted.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

Author: Sebastian Pop (sebpop)

Changes

when compiling with g++ 13.3.0 flang build fails with:

llvm-project/flang/lib/Semantics/expression.cpp:424:17: error: possibly dangling reference to a temporary [-Werror=dangling-reference]
424 | const Symbol &coarraySymbol{ref.GetBase().GetLastSymbol()};
| ^~~~~~~~~~~~~
llvm-project/flang/lib/Semantics/expression.cpp:424:58: note: the temporary was destroyed at the end of the full expression ‘Fortran::evaluate::CoarrayRef::GetBase() const().Fortran::evaluate::NamedEntity::GetLastSymbol()’
424 | const Symbol &coarraySymbol{ref.GetBase().GetLastSymbol()};
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~

Keep the base in a temporary variable to make sure it is not deleted.

---

Full diff: https://github.com/llvm/llvm-project/pull/138793.diff

1 Files Affected:

• (modified) flang/lib/Semantics/expression.cpp (+2-1)

diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
index e139bda7e4950..35eb7b61429fb 100644
--- a/flang/lib/Semantics/expression.cpp
+++ b/flang/lib/Semantics/expression.cpp
@@ -421,7 +421,8 @@ static void CheckSubscripts(
 
 static void CheckSubscripts(
     semantics::SemanticsContext &context, CoarrayRef &ref) {
-  const Symbol &coarraySymbol{ref.GetBase().GetLastSymbol()};
+  const auto &base = ref.GetBase();
+  const Symbol &coarraySymbol{base.GetLastSymbol()};
   Shape lb, ub;
   if (FoldSubscripts(context, coarraySymbol, ref.subscript(), lb, ub)) {
     ValidateSubscripts(context, coarraySymbol, ref.subscript(), lb, ub);