[PATCH] D127641: [clang-cl][MSVC] Add default /Zc conformance arguments

[Hans Wennborg via Phabricator via cfe-commits]

hans added inline comments.


================
Comment at: clang/test/Driver/cl-zc.cpp:98
 // thread safe statics are off for versions < 19.
 // RUN: %clang_cl /c -### -fms-compatibility-version=18 -- %s 2>&1 | FileCheck -check-prefix=NoThreadSafeStatics %s
 // RUN: %clang_cl /Zc:threadSafeInit /Zc:threadSafeInit- /c -### -- %s 2>&1 | FileCheck -check-prefix=NoThreadSafeStatics %s
----------------
steplong wrote:
> This line will fail, but I can't find any documentation on thread safe statics being off for versions < 19. https://docs.microsoft.com/en-us/cpp/build/reference/zc-threadsafeinit-thread-safe-local-static-initialization?view=msvc-170 says Visual Studio 2015 implements this by default.
VS 2015 has _MSC_VER 1900.
The test was added here: https://github.com/llvm/llvm-project/commit/c371ff048df8731052976f4e628ed1861cf61cfd and I assume David verified locally that 19 is the real cutoff.
I just tested locally with VS 2013, and it is indeed off there

```
C:\src\tmp>type a.cc && cl -c a.cc && dumpbin /disasm a.obj
int g();

int f() {
    static int x = g();
    return x;
}
Microsoft (R) C/C++ Optimizing Compiler Version 18.00.31101 for x86
Copyright (C) Microsoft Corporation.  All rights reserved.

a.cc
Microsoft (R) COFF/PE Dumper Version 12.00.31101.0
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file a.obj

File Type: COFF OBJECT

?f@@YAHXZ (int __cdecl f(void)):
  00000000: 55                 push        ebp
  00000001: 8B EC              mov         ebp,esp
  00000003: A1 00 00 00 00     mov         eax,dword ptr [?$S1@?1??f@@YAHXZ at 4IA]
  00000008: 83 E0 01           and         eax,1
  0000000B: 75 19              jne         00000026
  0000000D: 8B 0D 00 00 00 00  mov         ecx,dword ptr [?$S1@?1??f@@YAHXZ at 4IA]
  00000013: 83 C9 01           or          ecx,1
  00000016: 89 0D 00 00 00 00  mov         dword ptr [?$S1@?1??f@@YAHXZ at 4IA],ecx
  0000001C: E8 00 00 00 00     call        ?g@@YAHXZ
  00000021: A3 00 00 00 00     mov         dword ptr [?x@?1??f@@YAHXZ at 4HA],eax
  00000026: A1 00 00 00 00     mov         eax,dword ptr [?x@?1??f@@YAHXZ at 4HA]
  0000002B: 5D                 pop         ebp
  0000002C: C3                 ret

  Summary

           8 .bss
          64 .debug$S
          2F .drectve
          2D .text$mn
```


================
Comment at: clang/tools/driver/driver.cpp:237
 
+static void insertDefaultClangCLZcConformanceArgs(
+    SmallVectorImpl<const char *> &ArgVector) {
----------------
Instead of injecting flags like this which seems a bit crude and won't work in non-clang-cl mode, can't we just enable these features keyed off the MSVC version like we already do for e.g. thread-safe statics?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D127641/new/

https://reviews.llvm.org/D127641