Re: [RFC PATCH, i386]: Allow zero_extended addresses (+ problems with reload and offsetable address, "o" constraint)

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Aug 8, 2011 at 10:11 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Mon, Aug 8, 2011 at 5:30 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
>> Uros Bizjak wrote:
>>
>>> Although, it would be nice for reload to subsequently fix CSE'd
>>> non-offsetable memory by copying address to temporary reg (*as said in
>>> the documentation*), we could simply require an XMM temporary for
>>> TImode reloads to/from integer registers, and this fixes ICE for x32.
>>
>> Moves are special as far as reload is concerned. ?If there is already
>> a move instruction present *before* reload, it will get fixed up
>> according to its constraints as any other instruction.
>>
>> However, reload will *introduce* new moves as part of its operation,
>> and those will *not* themselves get reloaded. ?Instead, reload simply
>> assumes that every plain move will just succeed without requiring
>> any reload; if this is not true, the target *must* provide a
>> secondary reload for this move.
>>
>> (Note that the secondary reload could also work by reloading the
>> target address into a temporary; that's up to the target to
>> implement.)
>
> Whoa, indeed.
>
> Using attached patch that reloads memory address instead of going
> through XMM register, the code for the testcase improves from:
>
> test:
> .LFB0:
> ? ? ? ?.cfi_startproc
> ? ? ? ?pushq ? %rbx
> ? ? ? ?.cfi_def_cfa_offset 16
> ? ? ? ?.cfi_offset 3, -16
> ? ? ? ?sall ? ?$4, %esi
> ? ? ? ?addl ? ?%edi, %esi
> ? ? ? ?movdqa ?(%esi), %xmm0
> ? ? ? ?movdqa ?%xmm0, -16(%rsp)
> ? ? ? ?movq ? ?-16(%rsp), %rcx
> ? ? ? ?movq ? ?-8(%rsp), %rbx
> ? ? ? ?addq ? ?$1, %rcx
> ? ? ? ?adcq ? ?$0, %rbx
> ? ? ? ?movq ? ?%rcx, -16(%rsp)
> ? ? ? ?sall ? ?$4, %edx
> ? ? ? ?movq ? ?%rbx, -8(%rsp)
> ? ? ? ?movdqa ?-16(%rsp), %xmm0
> ? ? ? ?movdqa ?%xmm0, (%esi)
> ? ? ? ?pxor ? ?%xmm0, %xmm0
> ? ? ? ?movdqa ?%xmm0, (%edx,%esi)
> ? ? ? ?popq ? ?%rbx
> ? ? ? ?.cfi_def_cfa_offset 8
> ? ? ? ?ret
>
> to:
>
> test:
> .LFB0:
> ? ? ? ?.cfi_startproc
> ? ? ? ?sall ? ?$4, %esi
> ? ? ? ?pushq ? %rbx
> ? ? ? ?.cfi_def_cfa_offset 16
> ? ? ? ?.cfi_offset 3, -16
> ? ? ? ?addl ? ?%edi, %esi
> ? ? ? ?pxor ? ?%xmm0, %xmm0
> ? ? ? ?mov ? ? %esi, %eax
> ? ? ? ?movq ? ?(%rax), %rcx
> ? ? ? ?movq ? ?8(%rax), %rbx
> ? ? ? ?addq ? ?$1, %rcx
> ? ? ? ?adcq ? ?$0, %rbx
> ? ? ? ?sall ? ?$4, %edx
> ? ? ? ?movq ? ?%rcx, (%rax)
> ? ? ? ?movq ? ?%rbx, 8(%rax)
> ? ? ? ?movdqa ?%xmm0, (%edx,%esi)
> ? ? ? ?popq ? ?%rbx
> ? ? ? ?.cfi_def_cfa_offset 8
> ? ? ? ?ret
>
> H.J., can you please test attached patch? This optimization won't
> trigger on x86_64 anymore.
>

I will test it.

Thanks.


-- 
H.J.