On Fri, Oct 10, 2014 at 3:44 PM, Evgeniya Maenkova
<[email protected]> 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);
