[clang] [C++26][clang] Implement P2795R5 'Erroneous behaviour for uninitialized reads' (PR #177614)

[Reid Kleckner via cfe-commits]

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@@ -2012,7 +2026,7 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
     if (emission.IsEscapingByRef && !locIsByrefHeader)
       Loc = emitBlockByrefAddress(Loc, &D, /*follow=*/false);
 
-    return emitZeroOrPatternForAutoVarInit(type, D, Loc);
+    return emitZeroOrPatternForAutoVarInit(type, D, Loc, trivialAutoVarInit);
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rnk wrote:

Does the paper require compilers to initialize fields of records in addition to trivial variables? Otherwise, you can still trigger UB if the constructor leaves fields uninitialized, as in cases like this, where we return `undef`:
https://godbolt.org/z/zaWcWhdPP

https://github.com/llvm/llvm-project/pull/177614