[PATCH] D153701: [Clang] Implement P2718R0 "Lifetime extension in range-based for loops"

Fri Jul 7 05:08:13 PDT 2023

yronglin marked an inline comment as done.
yronglin added inline comments.

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Comment at: clang/lib/Sema/SemaExprCXX.cpp:8901-8914
+  // [P2718R0] Lifetime extension in range-based for loops.
+  //
+  // 6.7.7 [class.temporary] p5:
+  // There are four contexts in which temporaries are destroyed at a different
+  // point than the end of the full-expression.
+  //
+  // 6.7.7 [class.temporary] p6:
----------------
rsmith wrote:
> This isn't the right way to model the behavior here -- the presence or absence of an `ExprWithCleanups` is just a convenience to tell consumers of the AST whether they should expect to see cleanups later or not, and doesn't carry an implication of affecting the actual temporary lifetimes and storage durations.
> 
> The outcome that we should be aiming to reach is that all `MaterializeTemporaryExpr`s created as part of processing the for-range-initializer are marked as being lifetime-extended by the for-range variable. Probably the simplest way to handle that would be to track the current enclosing for-range-initializer variable in the `ExpressionEvaluationContextRecord`, and whenever a `MaterializeTemporaryExpr` is created, if there is a current enclosing for-range-initializer, mark that `MaterializeTemporaryExpr` as being lifetime-extended by it.
Awesome! Thanks a lot for your advice, this is very helpful! I want to take a longer look at it.

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  https://reviews.llvm.org/D153701/new/

https://reviews.llvm.org/D153701