https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83327
Tom de Vries <vries at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Attachment #42817|0 |1
is obsolete| |
--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 42850
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42850&action=edit
Tentative trunk patch
I've re-enabled i86_spill_class on trunk, added a printf when the optimization
is effective and build gcc on my laptop (with kaby lake cpu) with march=haswell
enabled by default.
I investigated the trigger:
...
Spill r87 into hr24 for fn __eqtf2 in libgcc/soft-fp/eqtf2.c
...
and observed that the life-range r87 is stretched over different basic blocks.
Then I added a "lra_create_live_ranges (lra_reg_spill_p, true)" after lra_spill
to force the live range analysis to run.
I observed that the live range analysis was only run once, meaning that the
hr24 usage is not propagated, which is AFAIU a reproduction of the root cause
of this PR.
I added code to the end of process_bb_lives to trigger the second live range
analysis:
...
@@ -1049,6 +1049,24 @@ process_bb_lives (basic_block bb, int &curr_point, bool
dead_insn_p)
check_pseudos_live_through_calls (j, last_call_used_reg_set);
}
+ for (i = 0; i < FIRST_PSEUDO_REGISTER; ++i)
+ {
+ if (!TEST_HARD_REG_BIT (hard_regs_live, i))
+ continue;
+
+ if (!TEST_HARD_REG_BIT (hard_regs_spilled_into, i))
+ continue;
+
+ if (bitmap_bit_p (df_get_live_in (bb), i))
+ continue;
+
+ live_change_p = true;
+ if (lra_dump_file)
+ fprintf (lra_dump_file,
+ " hard reg r%d is added to live at bb%d start\n", i,
bb->index);
+ bitmap_set_bit (df_get_live_in (bb), i);
+ }
+
if (need_curr_point_incr)
next_program_point (curr_point, freq);
...
and ran into the assert at the end of lra_create_live_ranges because although
the register is noted as changing liveness, it's still not propagated, and we
don't reach fixed point.
I then added fixes in make_hard_regno_{born,dead} in the same style as the fix
for PR82353, and that allowed the live info to be propagated.
