[AsmPrinter] Allow emitting codeview for any windows target

[mstorsjo]

Summary

Before SVN r244158, codeview debug info was emitted always emitted for msvc if debug info was enabled, but that commit added a module flag.

Since it's still restricted by the flag, we can allow it for any target if the user requests it, not only msvc (and windows-itanium, added in SVN r287567).

Add a test for emitting it for a mingw target.

[mstorsjo]

Tests with this with a mingw target look like it's working fine, but on x86_64, the VS debugger can't traverse the call stack if using dwarf for exception handling; that requires using SEH. (On i386, the debugger doesn't seem to rely on any specific exception handling mechanism.)

[mstorsjo]

Actually check for windows instead of allowing any os

[rnk]

lgtm

One thing that users will need to look out is that Microsoft debuggers make assumptions about how the C++ ABI works. If you debug classes with interesting virtual adjustments, you probably won't see the right data members. At some point, it might be good to write a holistic document about Clang's Windows support, detailing which features are available in mingw vs msvc environments. Maybe we already have one that I forgot about.

[mstorsjo]

In D46303#1091664, @rnk wrote:

lgtm

One thing that users will need to look out is that Microsoft debuggers make assumptions about how the C++ ABI works. If you debug classes with interesting virtual adjustments, you probably won't see the right data members. At some point, it might be good to write a holistic document about Clang's Windows support, detailing which features are available in mingw vs msvc environments. Maybe we already have one that I forgot about.

Thanks for letting me know about that! Another detail I noticed so far, is that the debugger requires SEH in order to traverse the call stack on x86_64 (and I normally build with dwarf for exceptions, and one can*t have both enabled at the same time), but on i386 it doesn't matter what I use.

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

if (!M.getModuleInlineAsm().empty()) {
     EmitInlineAsm(M.getModuleInlineAsm()+"\n",
                   OutContext.getSubtargetCopy(*STI), TM.Options.MCOptions);
     OutStreamer->AddComment("End of file scope inline assembly");
     OutStreamer->AddBlankLine();
   }
 
   if (MAI->doesSupportDebugInformation()) {
     bool EmitCodeView = MMI->getModule()->getCodeViewFlag();
-    if (EmitCodeView && (TM.getTargetTriple().isKnownWindowsMSVCEnvironment() ||
-                         TM.getTargetTriple().isWindowsItaniumEnvironment())) {
+    if (EmitCodeView && TM.getTargetTriple().isOSWindows()) {
       Handlers.push_back(HandlerInfo(new CodeViewDebug(this),
                                      DbgTimerName, DbgTimerDescription,
                                      CodeViewLineTablesGroupName,
                                      CodeViewLineTablesGroupDescription));
     }
     if (!EmitCodeView || MMI->getModule()->getDwarfVersion()) {
       DD = new DwarfDebug(this, &M);
       DD->beginModule();

test/DebugInfo/COFF/simple.ll

 ; RUN: llc -mcpu=core2 -mtriple=i686-pc-win32 -O0 < %s | FileCheck --check-prefix=X86 %s
 ; RUN: llc -mcpu=core2 -mtriple=i686-pc-win32-itanium -O0 < %s | FileCheck --check-prefix=X86 %s
+; RUN: llc -mcpu=core2 -mtriple=i686-pc-win32-gnu -O0 < %s | FileCheck --check-prefix=X86 %s
 ; RUN: llc -mcpu=core2 -mtriple=i686-pc-win32 -o - -O0 < %s | llvm-mc -triple=i686-pc-win32 -filetype=obj | llvm-readobj -s -sr -codeview -section-symbols | FileCheck --check-prefix=OBJ32 %s
 ; RUN: llc -mcpu=core2 -mtriple=i686-pc-win32-itanium -o - -O0 < %s | llvm-mc -triple=i686-pc-win32 -filetype=obj | llvm-readobj -s -sr -codeview -section-symbols | FileCheck --check-prefix=OBJ32 %s
+; RUN: llc -mcpu=core2 -mtriple=i686-pc-win32-gnu -o - -O0 < %s | llvm-mc -triple=i686-pc-win32 -filetype=obj | llvm-readobj -s -sr -codeview -section-symbols | FileCheck --check-prefix=OBJ32 %s
 ; RUN: llc -mcpu=core2 -mtriple=x86_64-pc-win32 -O0 < %s | FileCheck --check-prefix=X64 %s
 ; RUN: llc -mcpu=core2 -mtriple=x86_64-pc-win32-itanium -O0 < %s | FileCheck --check-prefix=X64 %s
+; RUN: llc -mcpu=core2 -mtriple=x86_64-pc-win32-gnu -O0 < %s | FileCheck --check-prefix=X64 %s
 ; RUN: llc -mcpu=core2 -mtriple=x86_64-pc-win32 -o - -O0 < %s | llvm-mc -triple=x86_64-pc-win32 -filetype=obj | llvm-readobj -s -sr -codeview -section-symbols | FileCheck --check-prefix=OBJ64 %s
 ; RUN: llc -mcpu=core2 -mtriple=x86_64-pc-win32-itanium -o - -O0 < %s | llvm-mc -triple=x86_64-pc-win32 -filetype=obj | llvm-readobj -s -sr -codeview -section-symbols | FileCheck --check-prefix=OBJ64 %s
+; RUN: llc -mcpu=core2 -mtriple=x86_64-pc-win32-gnu -o - -O0 < %s | llvm-mc -triple=x86_64-pc-win32 -filetype=obj | llvm-readobj -s -sr -codeview -section-symbols | FileCheck --check-prefix=OBJ64 %s
 
 ; This LL file was generated by running clang on the following code:
 ; D:\test.c:
 ; 1 void g(void);
 ; 2
 ; 3 void f(void) {
 ; 4   g();
 ; 5 }