[clang] [Clang] Extend lifetime of temporaries in mem-default-init for P2718R0 (PR #86960)

[Eli Friedman via cfe-commits]

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@@ -1230,11 +1230,26 @@ CodeGenFunction::EmitCXXForRangeStmt(const CXXForRangeStmt &S,
   JumpDest LoopExit = getJumpDestInCurrentScope("for.end");
 
   LexicalScope ForScope(*this, S.getSourceRange());
+  const DeclStmt *RangeDS = cast<DeclStmt>(S.getRangeStmt());
+  const VarDecl *RangeVar = cast<VarDecl>(RangeDS->getSingleDecl());
+  if (getLangOpts().CPlusPlus23)
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efriedma-quic wrote:

The AST in the `B{A()}` case looks like the following.  If your patch changes the AST for `B{}` to look the same, it should be fine, I think?  From your description, I'm not exactly sure what's different about what CXXDefaultInitExpr rewriting generates.

```
      | `-VarDecl 0xc4927c0 <col:113, col:118> col:113 implicit used __range1 'B &&' cinit
      |   `-ExprWithCleanups 0xc492aa8 <col:113, col:118> 'B' xvalue
      |     `-MaterializeTemporaryExpr 0xc492a00 <col:113, col:118> 'B' xvalue extended by Var 0xc4927c0 '__range1' 'B &&'
      |       `-CXXFunctionalCastExpr 0xc492678 <col:113, col:118> 'B' functional cast to B <NoOp>
      |         `-InitListExpr 0xc492508 <col:114, col:118> 'B'
      |           `-MaterializeTemporaryExpr 0xc492568 <col:115, col:117> 'const A' lvalue extended by Var 0xc4927c0 '__range1' 'B &&'
      |             `-ImplicitCastExpr 0xc492550 <col:115, col:117> 'const A' <NoOp>
      |               `-CXXBindTemporaryExpr 0xc4718c8 <col:115, col:117> 'A' (CXXTemporary 0xc4718c8)
      |                 `-CXXTemporaryObjectExpr 0xc471890 <col:115, col:117> 'A' 'void ()'
```

https://github.com/llvm/llvm-project/pull/86960