[clang] [clang][CompundLiteralExpr] Don't defer evaluation for CLEs (PR #137163)

[Eli Friedman via cfe-commits]

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@@ -9125,9 +9126,25 @@ bool
 LValueExprEvaluator::VisitCompoundLiteralExpr(const CompoundLiteralExpr *E) {
   assert((!Info.getLangOpts().CPlusPlus || E->isFileScope()) &&
          "lvalue compound literal in c++?");
-  // Defer visiting the literal until the lvalue-to-rvalue conversion. We can
-  // only see this when folding in C, so there's no standard to follow here.
-  return Success(E);
+  APValue *Lit;
+  // If CompountLiteral has static storage, its value can be used outside
+  // this expression. So evaluate it once and store it in ASTContext.
+  if (E->hasStaticStorage()) {
+    Lit = E->getOrCreateStaticValue(Info.Ctx);
+    Result.set(E);
+    // Reset any previously evaluated state, otherwise evaluation below might
+    // fail.
+    // FIXME: Should we just re-use the previously evaluated value instead?
+    *Lit = APValue();
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efriedma-quic wrote:

The evaluation should produce the same result every time, so it doesn't really do any harm to do it twice. But if you do it right, it's also very easy to avoid evaluating it twice.

I suspect using EvaluateInPlace will cause state to leak into the evaluation when it shouldn't (like, we accidentally accept a use of a temporary inside the initializer).

https://github.com/llvm/llvm-project/pull/137163