Re: [avr-llvm-devel] Inline assembly. Mostly just a stub.

[Stepan D. <stp...@na...>]

Hi Borja,
So, can I commit that memory constraint patch?

-Stepan.

Stepan Dyatkovskiy wrote:
> Hi Borja,
>
>  > Ahh, I didn't know avr-gcc was buggy on this feature, that's probably
>> the reason for why the code i pasted in my previous email didn't work.
> ...
>> What's wrong with clang? I fixed clang inline asm support back on
>> friday, so is there anything else that is broken?
> It should emit '*Q' instead of 'Q'. That's why code from prev. email
> didn't work, just compare -emit-llvm -S output of avr-clang with other
> backends,
>
>  > About the getPointerRegClass function, what is it used for? Also, please
>  > move the implementation to the cpp file instead of leaving it in the .h.
> Currently, it is used in registers coelescing pass. While being
> registers inflating, llvm lookups all register uses. If it found that
> register is used by inline-asm as memory operand, it requests the
> pointer class with this method (I think the largest one). But may be in
> future this method will be used in more cases.
>
> avr-gcc has buggy implementation of memory constraint, that's why
> avr-libs doesn't use it at all. We have a chance to be first here :-)
>
> -Stepan
>
>>
>>
>>
>> 2013/6/25 Stepan Dyatkovskiy <stp...@na...
>> <mailto:stp...@na...>>
>>
>>     Hi Borja.
>>     This is new patch. Seems I've moved memory constraint implementation
>>     to the same level like all other constraints. Note avr-gcc has buggy
>>     implementation of memory constraint, that's why *avr-libc doesn't
>>     use it*.
>>
>>     I removed restriction for Y,Z in getLargestLegalSuperClass, so these
>>     registers could be inflated now. But there was unimplemented
>>     getPointerRegClass method in AVRRegistersInfo. So currently I have
>>     restricted it to Y and Z. Though suppose we can extend it in future
>>     to XYZ set.
>>     Look changes in inline-asm.ll to see what exactly is supported now.
>>
>>     About clang.
>>     May be we ask John Myers to fix clang support for inline asm?
>>
>>     -Stepan.
>>
>>
>>     Stepan Dyatkovskiy wrote:
>>
>>         The patch. Forgot to attach it.
>>         -Stepan.
>>         Stepan Dyatkovskiy wrote:
>>
>>             Hi Borja,
>>
>>               > What happens in your example above when you use a real
>>             instruction
>>             like
>>
>>                 for example LDD? Does it still use GPR8 regs? To me it's
>>                 weird that if
>>                 you use a real instruction where operands are clearly
>>                 defined in the td
>>                 file the instruction selector uses  an invalid regclass.
>>
>>
>>             There are two kinds of inline asm support in LLVM:
>>             1. You just support all the constraints and pastes
>>             inline-asm contents
>>             as-is. That's why its still allowed to use names like
>>             "some_instr".
>>             2. You may expand inline-asm strings set, or in another
>>             words just parse
>>             it onto set of instructions. In this case you have to
>> implement
>>             TargetLowering::__ExpandInlineAsm method.
>>             I'd want to start it on this week though...
>>
>>             But first we have to get avr-libc compilable (perhpas I
>> read you
>>             thoughts ;-) )
>>
>>             Relative to memory constrains. I implemented initial version
>>             it can
>>             catch simplest cases (from test-case):
>>
>>             @a = internal global i16 0, align 4
>>             @b = internal global i16 0, align 4
>>             define void @mem() {
>>                 ;CHECK: some_instr Z, Y
>>                 call void asm "some_instr $0, $1", "=*Q,=*Q"(i16* @a,
>>             i16* @b)
>>                 ret void
>>             }
>>
>>             The patch is attached.
>>
>>             Its in my todo yet, to handle local variables. They could be
>>             emitted as
>>             Y+q expression. Hope to present this support tomorrow. So if
>>             'a' and 'b'
>>             from example above would be local we could get "some_instr
>>             Y, Y+2"
>>
>>             -Stepan.
>>
>>
>>
>>
>>
>