[PATCH] D63157: C++ DR712 and others: handle non-odr-use resulting from an lvalue-to-rvalue conversion applied to a member access or similar not-quite-trivial lvalue expression.

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added inline comments.


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Comment at: lib/CodeGen/CGExpr.cpp:1429
+/// for instance if a block or lambda or a member of a local class uses a
+/// const int variable or constexpr variable from an enclosing function.
 CodeGenFunction::ConstantEmission
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rjmccall wrote:
> Isn't the old comment correct here?  This is mandatory because of the enclosing-local-scope issues; that might be an "optimization" in the language, but it's not an optimization at the IRGen level because Sema literally is forcing us to do it. 
In the absence of this code, we'd emit the variable as a global constant from `EmitDeclRefLValue` in the enclosing-local-scope case (as we now do in the more-complex cases), so this should never be necessary for correct code generation any more.


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Comment at: lib/Sema/SemaExpr.cpp:15808
+namespace {
+// Helper to copy the template arguments from a DeclRefExpr or MemberExpr.
+class CopiedTemplateArgs {
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rjmccall wrote:
> This is really cute; I might steal this idea.  That said, it's probably worth explaining the lifetime mechanics here so that non-experts can understand how this works.
Done. I also added a `[[clang::lifetimebound]]` attribute so we'll get a warning if this is misused.


Repository:
  rC Clang

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63157/new/

https://reviews.llvm.org/D63157