https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68498
Bug ID: 68498
Summary: Replace LOOPS_MAY_HAVE_MULTIPLE_LATCHES with
LOOPS_HAVE_SINGLE_LATCH
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: other
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
Consider apply_loop_flags:
...
static void
apply_loop_flags (unsigned flags)
{
if (flags & LOOPS_MAY_HAVE_MULTIPLE_LATCHES)
{
/* If the loops may have multiple latches, we cannot canonicalize
them further (and most of the loop manipulation functions will
not work). However, we avoid modifying cfg, which some
passes may want. */
gcc_assert ((flags & ~(LOOPS_MAY_HAVE_MULTIPLE_LATCHES
| LOOPS_HAVE_RECORDED_EXITS)) == 0);
loops_state_set (LOOPS_MAY_HAVE_MULTIPLE_LATCHES);
}
else
disambiguate_loops_with_multiple_latches ();
/* Create pre-headers. */
if (flags & LOOPS_HAVE_PREHEADERS)
{
int cp_flags = CP_SIMPLE_PREHEADERS;
if (flags & LOOPS_HAVE_FALLTHRU_PREHEADERS)
cp_flags |= CP_FALLTHRU_PREHEADERS;
create_preheaders (cp_flags);
}
/* Force all latches to have only single successor. */
if (flags & LOOPS_HAVE_SIMPLE_LATCHES)
force_single_succ_latches ();
/* Mark irreducible loops. */
if (flags & LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS)
mark_irreducible_loops ();
if (flags & LOOPS_HAVE_RECORDED_EXITS)
record_loop_exits ();
}
...
Most properties in there have a handling bit: if property, do something.
The odd one out is LOOPS_MAY_HAVE_MULTIPLE_LATCHES, where we have if !property,
do something.
LOOPS_MAY_HAVE_MULTIPLE_LATCHES is not really a property, it's the absence of
LOOPS_MAY_HAVE_MULTIPLE_LATCHES that's a property, which we might call
LOOPS_HAVE_SINGLE_LATCH).
It would properly be better to replace uses of LOOPS_MAY_HAVE_MULTIPLE_LATCHES
with uses of LOOPS_HAVE_SINGLE_LATCH. We would get in apply_loop_flags:
...
if (flags & LOOPS_HAVE_SINGLE_LATCH)
disambiguate_loops_with_multiple_latches ();
else
{
/* If the loops may have multiple latches, we cannot canonicalize
them further (and most of the loop manipulation functions will
not work). However, we avoid modifying cfg, which some
passes may want. */
gcc_assert ((flags & ~(LOOPS_HAVE_RECORDED_EXITS)) == 0);
}
...
