> > gcc/ChangeLog:
> >
> > * loop-invariant.c (find_invariants_bb): Check profile count
> > before motion.
> > (find_invariants_body): Add argument.
> > ---
> > gcc/loop-invariant.c | 10 +++++++---
> > 1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/gcc/loop-invariant.c b/gcc/loop-invariant.c
> > index 5eee2e5c9f8..c61c8612fae 100644
> > --- a/gcc/loop-invariant.c
> > +++ b/gcc/loop-invariant.c
> > @@ -1183,9 +1183,14 @@ find_invariants_insn (rtx_insn *insn, bool
> > always_reached, bool always_executed)
> > call. */
> >
> > static void
> > -find_invariants_bb (basic_block bb, bool always_reached, bool
> > always_executed)
> > +find_invariants_bb (class loop *loop, basic_block bb, bool always_reached,
> > + bool always_executed)
> > {
> > rtx_insn *insn;
> > + basic_block preheader = loop_preheader_edge (loop)->src;
> > +
> > + if (preheader->count > bb->count)
> > + return;
>
> Please add a comment explaining the conditional and if possible also a
> testcase. Since profile updating and use is sensitive topic and it may
> trigger regressions later, it is important to keep track of info why
> given tests was added.
>
> I wonder why the cost model chose to move any invariatns to preheader
> why preheader->count > bb->count?
Thinking about this more, you want to test:
if (!always_executed && preheader->count > bb->count)
return;
This will rule out some profile misupates.
Also the code updating always_reached is worng:
if (always_reached
&& CALL_P (insn)
&& (RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)
|| ! RTL_CONST_OR_PURE_CALL_P (insn)))
always_reached = false;
It misses the case where statement can trhow external exception or
volatile asms that can also terminate execution.
I bit worry on how often the test will have false positives with guessed
profile where earlier loop optimizations reduced trip count below
realistic estimate.
Honza
>
> Honza
> >
> > FOR_BB_INSNS (bb, insn)
> > {
> > @@ -1214,8 +1219,7 @@ find_invariants_body (class loop *loop, basic_block
> > *body,
> > unsigned i;
> >
> > for (i = 0; i < loop->num_nodes; i++)
> > - find_invariants_bb (body[i],
> > - bitmap_bit_p (always_reached, i),
> > + find_invariants_bb (loop, body[i], bitmap_bit_p (always_reached, i),
> > bitmap_bit_p (always_executed, i));
> > }
> >
> > --
> > 2.25.1
> >
