[LLVMdev] ASM appears to be incorrect from llc

[Matthew Huck]

Hi,
  It doesn't compile with yasm, or nasm (reports invalid combination of
opcode and operands), and

mov _x,EAX

is meaningless as _x is just a label (an numeric constant that happens to
be an address), so it would have to be dereferenced to get to the memory at
that address, otherwise it's like saying

mov 0x12341234, EAX

Now, my asm skills are not that great, so I'm prepared to be told I'm
talking bollocks, but that's how I have interpreted everything I've read
today.

Cheers

Matthew


On Thu, Feb 16, 2012 at 1:11 PM, Eli Friedman <eli.friedman at gmail.com>wrote:

> On Wed, Feb 15, 2012 at 3:36 PM, Matthew Huck <matthew.huck at gmail.com>
> wrote:
> > Hi,
> >   I'm trying to compile an intermediate representation file to ASM (intel
> > style), and I believe that the resultant ASM is invalid. The IR is:
> >
> > ; ModuleID = 'test.u'
> >
> > %vec2 = type { float, float }
> > @t = global %vec2 zeroinitializer
> > @x = global i32 0
> >
> > define i32 @main__i__v() nounwind {
> > locals:
> >   %0 = load float* getelementptr inbounds (%vec2* @t, i32 0, i32 0)
> >   %1 = fptosi float %0 to i64
> >   %2 = trunc i64 %1 to i32
> >   store i32 %2, i32* @x
> >   ret i32 0
> > }
> >
> >
> >
> > Now, I know no memory is allocated for t (ignore that), we'll just expect
> > the final program to crash
> >
> > Running this through
> > llvm-as.exe test.trunk.ll -f -o test.bc
> > and then
> > llc -x86-asm-syntax=intel -o test.trunk.S test.bc
> >
> > yields:
> >
> > .def _main__i__v;
> > .scl 2;
> > .type 32;
> > .endef
> > .text
> > .globl _main__i__v
> > .align 16, 0x90
> > _main__i__v:                            # @main__i__v
> > # BB#0:                                 # %locals
> > sub ESP, 20
> > movss XMM0, DWORD PTR [_t]
> > movss DWORD PTR [ESP + 8], XMM0
> > fld DWORD PTR [ESP + 8]
> > fisttp QWORD PTR [ESP]
> > mov EAX, DWORD PTR [ESP]
> > mov _x, EAX
> > xor EAX, EAX
> > add ESP, 20
> > ret
> >
> > .data
> > .globl _t                      # @t
> > .align 8
> > _t:
> > .zero 8
> >
> > .globl _x                      # @x
> > .align 4
> > _x:
> > .long 0                       # 0x0
> >
> >
> >
> >
> > Now, the bit I think is wrong is
> > mov _x,EAX
> >
> > I think it should be
> > mov [_x], eax
> >
> > Thoughts?
>
> What makes you think it's wrong?
>
> -Eli
>
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