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

[via cfe-commits]

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@@ -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() &&
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yronglin wrote:

Yeah, I think so. we previously didn't materialize temporary object may should also be in compliance with the standard words "the materialization of a temporary object is generally delayed as long as possible in order to avoid creating unnecessary temporary object".

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