[PATCH] D155431: [CMake] Clean up old code for handling MSVC runtime setting the old way

Thu Sep 28 05:51:43 PDT 2023

mstorsjo added a comment.

In D155431#4651666 <https://reviews.llvm.org/D155431#4651666>, @yurybura wrote:

>> That define should be set implicitly if `CMAKE_MSVC_RUNTIME_LIBRARY` is set to one of the debug choices, no?
>
> I think, no. At least I cannot find information about this in CMake documentation <https://cmake.org/cmake/help/latest/variable/CMAKE_MSVC_RUNTIME_LIBRARY.html>.

It's not set explicitly by CMake, but if you set `CMAKE_MSVC_RUNTIME_LIBRARY` to `MultiThreadedDebug` or `MultiThreadedDebugDLL`, it passes `-MTd` or `-MDd` to the compiler. When the compiler gets either of those, it implicitly sets `-D_DEBUG`. Example:

  $ cat crtdefs.c 
  #ifdef _DEBUG
  #error _DEBUG
  #endif
  $ cl -c crtdefs.c -MDd
  Microsoft (R) C/C++ Optimizing Compiler Version 19.30.30705 for x64
  Copyright (C) Microsoft Corporation.  All rights reserved.

  crtdefs.c
  crtdefs.c(2): fatal error C1189: #error:  _DEBUG

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D155431/new/

https://reviews.llvm.org/D155431