[all-commits] [llvm/llvm-project] cf8fd2: [C] Make (c ? e1 : e2) noreturn only if both e1 an...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: cf8fd210a35c8e93136cb8edc5c6a2e818dc1b1d
      https://github.com/llvm/llvm-project/commit/cf8fd210a35c8e93136cb8edc5c6a2e818dc1b1d
  Author: Fangrui Song <i at maskray.me>
  Date:   2023-01-05 (Thu, 05 Jan 2023)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/AST/ASTContext.h
    M clang/lib/AST/ASTContext.cpp
    M clang/lib/Sema/SemaExpr.cpp
    M clang/test/CodeGen/attr-noreturn.c

  Log Message:
  -----------
  [C] Make (c ? e1 : e2) noreturn only if both e1 and e2 are noreturn

In C mode, if e1 has __attribute__((noreturn)) but e2 doesn'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, matching GCC.

`_Noreturn` and `[[noreturn]]` do not have the aforementioned problem.

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

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D140868