[Windows] Support MSVC __asm syntax

[timurrrr]

Bugzilla Link	13340
Resolution	FIXED
Resolved on	Sep 21, 2015 22:07
Version	trunk
OS	Windows NT
Depends On	llvm/llvm-bugzilla-archive#16830 llvm/llvm-bugzilla-archive#19861 llvm/llvm-bugzilla-archive#17201
Blocks	llvm/llvm-bugzilla-archive#13707
CC	@lattner,@DougGregor,@jrmuizel,@tritao,@nico,@rnk

Extended Description

$ cat assembly.cpp
int foo(int argument) {
int result;
__asm {
mov eax, argument
inc eax
mov result, eax
}
return result;
}

extern "C"
int printf(const char *fmt, ...);

int main() {
int val = 42;
int res = foo(val);
printf("res = %d\n", res);
return res != 43;
}

$ cl -nologo assembly.cpp && ./assembly.exe && echo "OK"
assembly.cpp
res = 43
OK

As of r159923,
$ clang++ -Xclang -cxx-abi -Xclang microsoft assembly.cpp && ./a.out && echo "OK"
assembly.cpp:3:3: warning: MS-style inline assembly is not supported [-Wmicrosoft]
__asm {
^
1 warning generated.
res = 11

[lattner]

Chad is working on this.

[timurrrr]

Oops, wrong platform.

[tritao]

What is the state of the asm support in trunk?

Can this be closed as fixed?

[timurrrr]

I think the support is not complete yet, e.g. this doesn't work IIRC:

__asm {
mov ecx, 1
L:
dec ecx
jnz L
}

[rnk]

Apparently this is also supported by MSVC:

struct Foo {
static int *ptr;
};

__asm {
mov eax, dword ptr [Foo::ptr]
mov byte ptr [eax], 66
}

Clang gives what you might expect:
$ clang -fsyntax-only namespace_asm.cpp
namespace_asm.cpp:10:28: error: Expected ']' token!
mov eax, dword ptr [Foo::ptr]
^

[llvmbot]

Tracking the issue pointed out by Reid in rdar://13499009. Should should be relatively easy to fix.

[llvmbot]

Reid, I'm unable to verify if your example is supported. With this example,

struct Foo {
static int *ptr;
};
void t() {
__asm mov eax, dword ptr [Foo::ptr]
}

I get the following errors:
C:\t.c(3) : error C2071: 'ptr' : illegal storage class
C:\t.c(6) : error C2400: inline assembler syntax error in 'third operand'; found ':'

I'm compiling with the /Od /Fa options using Visual Studio 10.

Am I doing something wrong?

[timurrrr]

Should be a .cpp file, I suppose?

[llvmbot]

Doh! That should have been obvious.. :o/ Thanks, Timur. The example works as expected.

[rnk]

MSVC asm using setc

[rnk]

Discovered one more bug: LLVM doesn't recognize the setc opcode. It's an alias for setb; they both check the carry flag (CF).

Test case attached.

[llvmbot]

The setc issue is also being tracked in rdar://13674398. Hopefully, I can address this shortly.

[llvmbot]

The setc issue should be resolved with r179804 and r179813.

[llvmbot]

*** Bug llvm/llvm-bugzilla-archive#15779 has been marked as a duplicate of this bug. ***

[rnk]

struct offsets to memory operands