This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.
| Index Nav: | [Date Index] [Subject Index] [Author Index] [Thread Index] | |
|---|---|---|
| Message Nav: | [Date Prev] [Date Next] | [Thread Prev] [Thread Next] |
| Other format: | [Raw text] | |
On Wed, Mar 30, 2016 at 9:09 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Thu, Mar 24, 2016 at 6:26 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
>> Hi,
>> Quite lot of time is used when IVOPT computes cost for <use, cand> pairs. As a matter of fact, some pairs are very similar to each other, and we can abstract and compute cost only once for these pairs. This is a patch doing so, the idea is skipping cost computation for sub-uses in each group, of course it may result in different assembly code for some complicated cases because it estimates cost rather than doing real computation. I did double check one of such case that the change in generated assembly is not degeneration. For an IVOPT heavy program (spec2k/173), this patch reduces IVOPT's compilation time by 7~8%, as well as the memory consumption on my developing machine.
>>
>> Bootstrap & test on x86_64.
>>
>> For spec2k6 data on x86_64. Maybe because I ran spec2k6 compiled with patched GCC in unclean environment, some cases are regressed by small amount (< %1). I manually compared assembly code for several cases, including ones with the largest regression (still within <1%). I could confirm that generated assembly code is exact the same as unpatched GCC, except for function emit_library_call_value_1 in 403.gcc/calls.c.
>>
>> In this case, difference of IVOPT dumps is as below:
>>
>> $ diff -y trunk/calls.c.154t.ivopts patch/calls.c.154t.ivopts
>>
>> <bb 44>: <bb 44>:
>> # val_21 = PHI <val_175(168), val_650(43)> # val_21 = PHI <val_175(168), val_650(43)>
>> _811 = (void *) ivtmp.322_829; _811 = (void *) ivtmp.322_829;
>> MEM[base: _811, offset: -48B] = val_21; | MEM[base: _811, offset: -32B] = val_21;
>> _810 = (void *) ivtmp.322_829; _810 = (void *) ivtmp.322_829;
>> MEM[base: _810, offset: -40B] = mode_163; | MEM[base: _810, offset: -24B] = mode_163;
>> _182 = function_arg (&args_so_far, mode_163, 0B, 1); _182 = function_arg (&args_so_far, mode_163, 0B, 1);
>> _809 = (void *) ivtmp.322_829; _809 = (void *) ivtmp.322_829;
>> MEM[base: _809, offset: -32B] = _182; | MEM[base: _809, offset: -16B] = _182;
>> _807 = (void *) ivtmp.322_829; _807 = (void *) ivtmp.322_829;
>> MEM[base: _807, offset: -24B] = 0; | MEM[base: _807, offset: -8B] = 0;
>> _185 = (struct args_size *) ivtmp.322_829; | _801 = ivtmp.322_829 + 16;
>> _801 = ivtmp.322_829 + 18446744073709551600; <
>> _800 = (struct args_size *) _801; _800 = (struct args_size *) _801;
>> _186 = _800; | _185 = _800;
>> > _186 = (struct args_size *) ivtmp.322_829;
>> _187 = _182 != 0B; _187 = _182 != 0B;
>> _188 = (int) _187; _188 = (int) _187;
>> locate_and_pad_parm (mode_163, 0B, _188, 0B, &args_size, _1 locate_and_pad_parm (mode_163, 0B, _188, 0B, &args_size, _1
>> _802 = (void *) ivtmp.322_829; _802 = (void *) ivtmp.322_829;
>> _190 = MEM[base: _802, offset: 8B]; | _190 = MEM[base: _802, offset: 24B];
>> if (_190 != 0B) if (_190 != 0B)
>> goto <bb 45>; goto <bb 45>;
>> else else
>> goto <bb 46>; goto <bb 46>;
>>
>> <bb 45>: <bb 45>:
>> fancy_abort ("calls.c", 3724, &__FUNCTION__); fancy_abort ("calls.c", 3724, &__FUNCTION__);
>>
>> It's only an offset difference in IV. And below is difference of generated assembly:
>> $ diff -y trunk/calls.S patch/calls.S
>> .L489: .L489:
>> leaq -80(%rbp), %rdi leaq -80(%rbp), %rdi
>> xorl %edx, %edx xorl %edx, %edx
>> movl $1, %ecx movl $1, %ecx
>> movl %r13d, %esi movl %r13d, %esi
>> movq %rax, -48(%r15) <
>> movl %r13d, -40(%r15) <
>> call function_arg <
>> movl $0, -24(%r15) <
>> movq %rax, -32(%r15) movq %rax, -32(%r15)
>> > movl %r13d, -24(%r15)
>> > call function_arg
>> xorl %edx, %edx xorl %edx, %edx
>> pushq %r12 | movq %rax, -16(%r15)
>> testq %rax, %rax testq %rax, %rax
>> pushq %r15 | leaq 16(%r15), %rax <--I1
>> leaq -16(%r15), %r9 | movl $0, -8(%r15)
>> leaq -112(%rbp), %r8 leaq -112(%rbp), %r8
>> > pushq %r12
>> setne %dl setne %dl
>> movl %r13d, %edi | movq %r15, %r9 <--I2
>> > pushq %rax <--I3
>> xorl %ecx, %ecx xorl %ecx, %ecx
>> xorl %esi, %esi xorl %esi, %esi
>> > movl %r13d, %edi
>> call locate_and_pad_parm call locate_and_pad_parm
>> cmpq $0, 8(%r15) | cmpq $0, 24(%r15)
>> popq %rax popq %rax
>> popq %rdx popq %rdx
>> jne .L602 jne .L602
>>
>> There is one additional move instruction (I2) after patching, but I believe it's a choice of RA. If we switch %rax/%r9 in instructions I1/I2 as below:
>> ...
>> leaq 16(%r15), %r9
>> ...
>> movq %r15, %rax
>> pushq %r15
>>
>> Then I2 becomes redundant and can be removed.
>>
>> I will collect performance data on AArch64 to make sure there is no breakage either. So is it OK?
>
> I think the patch is ok - note that I have a hard time following the
> code, esp. the 'first' flag.
>
> + /* Add cost for sub uses in group. */
> + do
> + {
> + /* Compute cost for the first sub_use with different offset to
> + the first one and use it afterwards, because the cost could
> + be very different if the offset is different. */
> + if (first && use->addr_offset != sub_use->addr_offset)
> + {
> + first = false;
> + sub_cost = get_computation_cost (data, sub_use, cand, true,
> + NULL, &can_autoinc, NULL);
> + if (infinite_cost_p (sub_cost))
> + {
> + cost = infinite_cost;
> + break;
> + }
> + }
> +
> + cost = add_costs (cost, sub_cost);
> + sub_use = sub_use->next;
> + }
> + while (sub_use);
>
> we start this loop with first = true, so for each sub-use we compute
> no new sub-cost until
> use->addr_offset changes for the first time after which we will never
> compute sub-cost
> again. So we call get_computation_cost at most twice for al sub-uses.
>
> I suppose all sub-uses have equal ->addr_base. Suppose sub-uses are then sorted
> after ->addr_offset what keeps that list from having three different
> addr_offset but
> with "very different cost"? There seems to be group_address_uses but
> that suggests
> the cost might be actually the same for all sub-uses.
>
> So adding a little explaining before the loop over sub-uses would be
> appreciated.
Thanks for reviewing. Here is the patch with trivially revised comments.
I also collected benchmark data for spec2k6 on AArch64, there is no
surprise except for case 456.hmmer. I double checked generated
assembly and can confirm it's not real.
Will apply the patch later.
Thanks,
bin
>
> Thanks,
> Richard.
>
>> Thanks,
>> bin
>>
>> 2016-03-23 Bin Cheng <bin.cheng@arm.com>
>>
>> * tree-ssa-loop-ivopts.c (struct comp_cost): New scrach field.
>> (no_cost, infinite_cost): Initialize the new field.
>> (get_computation_cost_at): Record setup cost.
>> (determine_use_iv_cost_address): Skip cost computation for sub
>> uses if we can estimate it without losing accuracy.
>>
Attachment:
ivopt-time-20160330.txt
Description: Text document
| Index Nav: | [Date Index] [Subject Index] [Author Index] [Thread Index] | |
|---|---|---|
| Message Nav: | [Date Prev] [Date Next] | [Thread Prev] [Thread Next] |