[Clang] - Massaging code to fix MSVS 2015 win32-release configuration

[grimar]

Summary

Microsoft Visual Studio Community 2015
Version 14.0.23107.0 D14REL

When building in release mode, MSVS failed with:

57>c:\access_softek\llvm\tools\clang\lib\ast\astcontext.cpp(334): fatal error C1001: An internal error has occurred in the compiler.
57> (compiler file 'f:\dd\vctools\compiler\utc\src\p2\main.c', line 246)
57> To work around this problem, try simplifying or changing the program near the locations listed above.

I little code simplification helped to workaround this.

[klimek]

Not sure whether it makes sense to work around compiler bugs in CL. I assume this happens with clang from trunk? Is there a bug filed against CL?

[yaron.keren]

clang can't generate Visual C++ debug info except line numbers yet, so building with VC is essential to development on Windows. While most people and our bots are still using VC 2013 going forward supporting VC 2015 (even with bugs) is worth a small patch.

[majnemer]

In D13203#257539, @klimek wrote:

Not sure whether it makes sense to work around compiler bugs in CL. I assume this happens with clang from trunk? Is there a bug filed against CL?

We do this with some regularity for MSVC and GCC.

ASTContext.cpp

367–374

We need a comment detailing that this is a workaround for MSVC 2015 so that it can be removed when we drop support for 2015.

[grimar]

Added comment per review request.

[klimek]

Note: with VS Professional 14.0.23107.0 D14REL I do not get this error.

[grimar]

r251415 fixes this in another way.

ASTContext.cpp

if (Pos != RedeclComments.end()) {
       if (Raw.getKind() != RawCommentAndCacheFlags::NoCommentInDecl) {
         RC = Raw.getRaw();
         OriginalDeclForRC = Raw.getOriginalDecl();
         break;
       }
     } else {
       RC = getRawCommentForDeclNoCache(I);
       OriginalDeclForRC = I;
-      RawCommentAndCacheFlags Raw;
+      // TODO: these next two lines helps to workaround msvs 2015
+      // internal compiler error. This is a replacement
+      // of delayed assignment RedeclComments[I] = Raw
+      // which caused that issue.
+      RedeclComments[I] = RawCommentAndCacheFlags();
+      RawCommentAndCacheFlags &Raw = RedeclComments[I];
+      //
       if (RC) {
         Raw.setRaw(RC);
         Raw.setKind(RawCommentAndCacheFlags::FromDecl);
       } else
         Raw.setKind(RawCommentAndCacheFlags::NoCommentInDecl);
       Raw.setOriginalDecl(I);
-      RedeclComments[I] = Raw;
       if (RC)
         break;
     }
   }
 
   // If we found a comment, it should be a documentation comment.
   assert(!RC || RC->isDocumentation());