[ARM] Allow using ';' as asm statement separator in MSVC mode

[mstorsjo]

Summary

This does the same as D96259, but for ARM, just like AArch64,
using the same comment char as for ELF and MinGW mode.

(I never heard back about any downstream problems from that
change, so I presume it didn't break anything.)

As the assembly input/output of LLVM is GAS style, trying to
match what MS armasm.exe does isn't needed (because the comment
char used is the least concern when it comes to that; all
directives differ too). If a separate armasm compatible mode
is implemented, it can use its own comment style (just like
llvm-ml implements MS ml.exe compatible assembly parsing).

This fixes building compiler-rt assembly files for ARM in MSVC
mode.

The updated testcase literals-comments.s was only intended to
make sure that '#' isn't interpreted as a comment char.

[mstorsjo]

Ping @rnk - we did something similar for aarch64 before.

[mstorsjo]

Improved the testcases a little.

[tambre]

LGTM. Maybe add a changelog entry?

[mstorsjo]

In D107251#2957996, @tambre wrote:

LGTM. Maybe add a changelog entry?

I guess it could be good, but as this goes to the main branch (I don't think it's worth requesting a backport of this) and the main branch's release notes generally are empty until after the branch, there's a risk of someone wiping them before the next release, so I think I'll leave it until then... I normally fill in the changelogs after a new release branch is created with things I've done anyway.

[rnk]

lgtm

llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp

 void ARMCOFFMCAsmInfoMicrosoft::anchor() { }
 
 ARMCOFFMCAsmInfoMicrosoft::ARMCOFFMCAsmInfoMicrosoft() {
   AlignmentIsInBytes = false;
   SupportsDebugInformation = true;
   ExceptionsType = ExceptionHandling::WinEH;
   PrivateGlobalPrefix = "$M";
   PrivateLabelPrefix = "$M";
-  CommentString = ";";
+  CommentString = "@";
 
   // Conditional Thumb 4-byte instructions can have an implicit IT.
   MaxInstLength = 6;
 }
 
 void ARMCOFFMCAsmInfoGNU::anchor() { }
 
 ARMCOFFMCAsmInfoGNU::ARMCOFFMCAsmInfoGNU() {

llvm/test/CodeGen/ARM/cfguard-checks.ll

lpad:                                             ; preds = %entry
   ; CHECK:       movt r0, :upper16:__guard_check_icall_fptr
   ; CHECK:       ldr r1, [r0]
   ; CHECK:       movw r4, :lower16:target_func
   ; CHECK:       movt r4, :upper16:target_func
   ; CHECK:       mov r0, r4
   ; CHECK:       blx r1
   ; CHECK-NEXT:  $Mtmp0:
   ; CHECK-NEXT:  blx r4
-  ; CHECK:       ; %common.ret
-  ; CHECK:       ; %lpad
+  ; CHECK:       @ %common.ret
+  ; CHECK:       @ %lpad
 }
 
 declare void @h()
 
 
 ; Test that longjmp targets have public labels and are included in the .gljmp section.
 %struct._SETJMP_FLOAT128 = type { [2 x i64] }
 @buf1 = internal global [16 x %struct._SETJMP_FLOAT128] zeroinitializer, align 16

llvm/test/MC/ARM/Windows/literals-comments.s

-; RUN: llvm-mc -triple armv7-windows-msvc -filetype obj -o - %s
+@ RUN: llvm-mc -triple armv7-windows-gnu -filetype obj -o %t.obj %s
+@ RUN: llvm-objdump -d %t.obj | FileCheck %s
+@ RUN: llvm-mc -triple armv7-windows-msvc -filetype obj -o %t.obj %s
+@ RUN: llvm-objdump -d %t.obj | FileCheck %s
 
   .syntax unified
   .thumb
 
   .text
 
   .global function
   .thumb_func
 function:
-  ; this is a comment
-  mov r0, #42 ; this # was not
+  @ this is a comment
+  mov r0, #42 @ this # was not
+  nop; nop @ This retains both instructions
   bx lr
+
+@ CHECK:  0: 4f f0 2a 00   mov.w   r0, #42
+@ CHECK:  4: 00 bf         nop
+@ CHECK:  6: 00 bf         nop
+@ CHECK:  8: 70 47         bx      lr