[LLVMdev] llvm register reload/spilling around calls

[Roland Scheidegger]

On 21.10.2010 01:31, Roland Scheidegger wrote:
> (repost with right sender address)
> 
> On 20.10.2010 18:13, Jakob Stoklund Olesen wrote:
>> On Oct 20, 2010, at 7:46 AM, Roland Scheidegger wrote:
>>
>>> On 20.10.2010 05:00, Jakob Stoklund Olesen wrote:
>>>> Look in X86InstrControl.td. The call instructions are all prefixed
>>>> by:
>>>>
>>>> let Defs = [RAX, RCX, RDX, RSI, RDI, R8, R9, R10, R11, FP0, FP1, FP2,
>>>> FP3, FP4, FP5, FP6, ST0, ST1, MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
>>>> XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, XMM8, XMM9, XMM10,
>>>> XMM11, XMM12, XMM13, XMM14, XMM15, EFLAGS],
>>>>
>>>> This is the fixed list of call-clobbered registers. It should really
>>>> be controlled by the calling convention of the called function
>>>> instead.
>>>>
>>>> The WINCALL* instructions only exist because of this.
>>> Ahh I see now. I hacked this up and indeed the code looks much better.
>>> I can't force it to use win64 calling conventions right?
>> No, only by targeting Windows.
>>
>>> Would do just fine for this case (much closer to a cold calling
>>> convention, I really only need 5 preserved xmm regs).
>> If XMM registers are the problem, -pre-alloc-split really ought to help you.
>>
>> You may want to investigate why it doesn't.
> 
> Ok, I see if I can figure out something, though I have no in-depth
> knowledge of llvm.
> I think only xmm regs are really a problem because r12-r15 are
> callee-saved and hence used for holding the most frequently used values,
> which seems to be enough to avoid spilling there.

I can't really see what's happening there. Any hints what to look at?

Roland