Fixing LLVM_BUILTIN_TRAP on Windows

[Reid Kleckner]

How is raising a 0xdeadd0d0 exception code better than an access violation?
The only way I think we could functionally improve over the access
violation is to have something that's known noreturn (like __builtin_trap)
and encodes smaller, like ud2a.

On Mon, Feb 9, 2015 at 9:02 AM, Aaron Ballman <aaron at aaronballman.com>
wrote:

> The implementation for LLVM_BUILTIN_TRAP on Windows leaves quite a bit
> to be desired. Instead of relying on writing to an invalid volatile
> pointer, which is hoped to result in raising an exception we can catch
> with the vectored exception handler, simply raise an exception
> manually.
>
> To prevent having to #include a Win32 header from Compiler.h, this
> patch forward declares the RaiseException call.
>
> The only functional difference between the current implementation and
> the new one is that RaiseException will appear on the stack traces now
> when invoking this macro. Eg)
>
> e:\llvm\2013>clang -fsyntax-only "E:\Aaron Ballman\Desktop\test.cpp"
> 0x755EC42D (0xDEADD0D0 0x00000001 0x00000000 0x00000000), RaiseException()
> + 0x5
> 8 bytes(s)
> 0x03D9F222 (0x00692018 0x00000000 0x0685E3C4 0x0685E3A0), `anonymous
> namespace':
> :PragmaDebugHandler::HandlePragma() + 0xC2 bytes(s),
> e:\llvm\llvm\tools\clang\li
> b\lex\pragma.cpp, line 870 + 0x13 byte(s)
> 0x03D997DC (0x00692018 0x00000000 0x0685E3C4 0x0685E494),
> clang::PragmaNamespace
> ::HandlePragma() + 0xBC bytes(s),
> e:\llvm\llvm\tools\clang\lib\lex\pragma.cpp, l
> ine 95 + 0x1B byte(s)
> ...
>
> instead of:
>
> e:\llvm\2013>clang -fsyntax-only "E:\Aaron Ballman\Desktop\test.cpp"
> 0x03CDF1CF (0x00302018 0x00000000 0x0679E5F8 0x0679E5D4), `anonymous
> namespace':
> :PragmaDebugHandler::HandlePragma() + 0xAF bytes(s),
> e:\llvm\llvm\tools\clang\li
> b\lex\pragma.cpp, line 870
> 0x03CD979C (0x00302018 0x00000000 0x0679E5F8 0x0679E6C8),
> clang::PragmaNamespace
> ::HandlePragma() + 0xBC bytes(s),
> e:\llvm\llvm\tools\clang\lib\lex\pragma.cpp, l
> ine 95 + 0x1B byte(s)
> ...
>
> ~Aaron
>
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