[clang] [Clang] Implement P2718R0 "Lifetime extension in range-based for loops" (PR #76361)

[Aaron Ballman via cfe-commits]

================
@@ -8244,11 +8229,33 @@ ExprResult Sema::IgnoredValueConversions(Expr *E) {
     //   If the expression is a prvalue after this optional conversion, the
     //   temporary materialization conversion is applied.
     //
-    // We skip this step: IR generation is able to synthesize the storage for
-    // itself in the aggregate case, and adding the extra node to the AST is
-    // just clutter.
-    // FIXME: We don't emit lifetime markers for the temporaries due to this.
-    // FIXME: Do any other AST consumers care about this?
+    // We do not materialize temporaries by default in order to avoid creating
+    // unnecessary temporary objects. If we skip this step, IR generation is
+    // able to synthesize the storage for itself in the aggregate case, and
+    // adding the extra node to the AST is just clutter.
+    if (ShouldMaterializePRValueInDiscardedExpression() &&
+        getLangOpts().CPlusPlus17 && E->isPRValue() &&
----------------
AaronBallman wrote:

Ah okay, so this is still related to the lifetime extension for range-based for loops -- we needed this bit for C++17 conformance which we previously didn't have to do?

(Mostly trying to reason about whether this is a separate bug fix that should be landed in a separate patch or whether this is related to the correctness for P2718R0.)

https://github.com/llvm/llvm-project/pull/76361