Got it, thanks.
(Now there are phi instead of if)
On Fri, Oct 10, 2014 at 6:18 PM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Fri, Oct 10, 2014 at 3:44 PM, Evgeniya Maenkova
> <evgeniya.maenk...@gmail.com> wrote:
>> Hi,
>> could anyone clarify about predicated code motion in lim?
>>
>> After reading a TODO in /tree-ssa-loop-im.c (see [1]) I tried several
>> examples, say [2]. However, in all of them the code was moved out of
>> the loop successfully (either by pre or by lim, as in [2]).
>>
>> So my question is: what the author of this code did mean by
>> "predicated code motion"? (what is the TODO)
>
> It means transforming
>
>> Thanks,
>>
>> Evgeniya
>>
>> [1]
>> TODO: Support for predicated code motion. I.e.
>>
>> while (1)
>> {
>> if (cond)
>> {
>> a = inv;
>> something;
>> }
>> }
>
> this to
>
> if (cond)
> {
> a= inv;
> something;
> }
> while (1)
> ;
>
> which is currently supported in a very limited way by emitting
> this as
>
> a = cond ? inv : a;
>
> for at most two statements. As it executes stmts unconditionally
> that way it is limited to non-trapping operations.
>
> Richard.
>
>
>> [2]
>>
>> void foo(int cond, int inv)
>> {
>>
>> int a;
>> int i = 0;
>> int j = 0;
>> while (j++ < 100) {
>> while (i++ < 2000)
>> {
>> if (j % 2)
>> {
>> a = 528*j;
>> printf("Hey1%d %d", a, i);//something;
>> }
>> }
>>
>> }
>> }
>>
>> lim:
>>
>> ;; Function foo (foo, funcdef_no=0, decl_uid=1394, cgraph_uid=0,
>> symbol_order=0)
>>
>> foo (int cond, int inv)
>> {
>> int j;
>> int i;
>> int a;
>> unsigned int j.0_12;
>> unsigned int _13;
>> unsigned int _18;
>> unsigned int _21;
>>
>> <bb 2>:
>> goto <bb 8>;
>>
>> <bb 3>:
>> if (_13 != 0)
>> goto <bb 4>;
>> else
>> goto <bb 10>;
>>
>> <bb 10>:
>> goto <bb 5>;
>>
>> <bb 4>:
>> printf ("Hey1%d %d", a_14, i_11);
>>
>> <bb 5>:
>>
>> <bb 6>:
>> # i_1 = PHI <i_22(8), i_11(5)>
>> i_11 = i_1 + 1;
>> if (i_1 <= 1999)
>> goto <bb 3>;
>> else
>> goto <bb 7>;
>>
>> <bb 7>:
>> # i_20 = PHI <i_11(6)>
>> j_9 = j_23 + 1;
>> if (j_23 != 100)
>> goto <bb 11>;
>> else
>> goto <bb 9>;
>>
>> <bb 11>:
>>
>> <bb 8>:
>> # i_22 = PHI <i_20(11), 0(2)>
>> # j_23 = PHI <j_9(11), 1(2)>
>> j.0_12 = (unsigned int) j_23;
>> _13 = j.0_12 & 1;
>> _21 = (unsigned int) j_23;
>> _18 = _21 * 528;
>> a_14 = (int) _18;
>> goto <bb 6>;
>>
>> <bb 9>:
>> return;
>>
>> }
>>
>>
>> However, in loopinit (the optimization before lim) there was no motion
>> (So this was done by lim:
>> <bb 4>:
>> a_14 = j_23 * 528;
>> printf ("Hey1%d %d", a_14, i_11);
--
Thanks,
Evgeniya
perfstories.wordpress.com
