Re: [df-scan.c] Optimise DF_REFs ordering in collection_rec, use HARD_REG_SETs instead of bitmaps

[Paolo Bonzini <bonzini@gnu.org>]

On 07/08/2011 11:05 AM, Dimitrios Apostolou wrote:
> On Fri, 8 Jul 2011, Jakub Jelinek wrote:
>> On Fri, Jul 08, 2011 at 06:20:04AM +0300, Dimitrios Apostolou wrote:
>>> The attached patch does two things for df_get_call_refs():
>>> * First it uses HARD_REG_SETs for defs_generated and
>>> regs_invalidated_by_call, instead of bitmaps. Replacing in total
>>> more than 400K calls (for my testcase) to bitmap_bit_p() with the
>>> much faster TEST_HARD_REG_BIT, reduces the total instruction count
>>> from about 13M to 1.5M.
>>
>> Have you verified that collection_rec->def_vec never contains pseudo
>> register references? Otherwise you couldn't use
>> HARD_REG_SET... gcc_checking_assert might be useful.
>>
>
> Hi Jakub, Steve pointed me to the following from GCC Internals Manual:
>
> call_insn insns have the same extra fields as insn insns, accessed in
> the same way and in addition contain a field CALL_INSN_FUNCTION_USAGE,
> which contains a list (chain of expr_list expressions) containing use
> and clobber expressions that denote hard registers and MEMs used or
> clobbered by the called function.
>
> So doesn't that mean that for CALL insns it should contain only HARD_REG
> DEFs? I will ofcourse use an assert to be sure.

That part is only for CALL_INSN_FUNCTION_USAGE, which is what 
df_get_call_refs handles.  However, if you rewrite the handling of 
defs_generated as required by your second patch, you'll then be sure 
that you will only have hard registers.

BTW, what testcase are you using?  I suggest that you try building 
stage1 with CFLAGS=--save-temps, and get some of the largest 
preprocessed .i files from there (combine and fold-const for example). 
You can then time them very easily from the old and new build 
directories, with "./cc1 /path/to/file.i -O2".

Paolo