[PATCH] D140868: [C] Make (c ? e1 : e2) noreturn only if both e1 and e2 are noreturn

[Fangrui Song via Phabricator via cfe-commits]

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In C mode, if e1 is noreturn but e2 isn't, `(c ? e1 : e2)` is
incorrectly noreturn and Clang codegen produces `unreachable` which may
lead to miscompiles (see [1] `gawk/support/dfa.c`).
This problem has been known since
8c6b56f39d967347f28dd9c93f1cffddf6d7e4cd (2010) or earlier.

Fix this by making the result type noreturn only if both e1 and e2 are
noreturn.

Fix https://github.com/llvm/llvm-project/issues/59792 [1]


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140868

Files:
  clang/include/clang/AST/ASTContext.h
  clang/lib/AST/ASTContext.cpp
  clang/lib/Sema/SemaExpr.cpp
  clang/test/CodeGen/attr-noreturn.c

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