fwprop may propagate a SET_SRC that contains the last use of a REG to a
later point, but it will leave the REG_DEAD note in place, even though
it is no longer correct. I noticed this while investigating PR50826:
the initialization of the internal_arg_pointer has a REG_DEAD note for
%r29, but even after it is fwpropped, the note remains there. This
patch fixes this bug.
It also reduces the risk of code divergence in VTA-enabled compilations,
by enabling the simpler test in all_uses_available_at when there are
debug insns between the def and the use.
Regstrapped on x86_64-linux-gnu and i686-linux-gnu. Ok to install?
for gcc/ChangeLog
from Alexandre Oliva <aol...@redhat.com>
* fwprop.c (all_uses_available_at): Skip debug insns.
(try_fwprop_subst): Drop outdated REG_DEAD notes.
Index: gcc/fwprop.c
===================================================================
--- gcc/fwprop.c.orig 2011-10-26 06:37:08.154321512 -0200
+++ gcc/fwprop.c 2011-10-26 06:52:44.163150398 -0200
@@ -801,7 +801,7 @@ all_uses_available_at (rtx def_insn, rtx
/* If target_insn comes right after def_insn, which is very common
for addresses, we can use a quicker test. */
- if (NEXT_INSN (def_insn) == target_insn
+ if (next_nondebug_insn (def_insn) == target_insn
&& REG_P (SET_DEST (def_set)))
{
rtx def_reg = SET_DEST (def_set);
@@ -1019,6 +1019,22 @@ try_fwprop_subst (df_ref use, rtx *loc,
}
}
+ if (ok)
+ {
+ rtx *link = ®_NOTES (def_insn);
+
+ while (*link)
+ if (REG_NOTE_KIND (*link) == REG_DEAD
+ && reg_mentioned_p (XEXP (*link, 0), new_rtx))
+ /* We could propagate the REG_DEAD note if we knew we're
+ propagating into what will become a death point.
+ Considering multiple uses in different BBs, some of which
+ may be debug uses requiring debug stmts to be introduced,
+ how about we just let DF take care of it? */
+ *link = XEXP (*link, 1);
+ else
+ link = &XEXP (*link, 1);
+ }
if ((ok || note) && !CONSTANT_P (new_rtx))
update_df (insn, note);
--
Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/ FSF Latin America board member
Free Software Evangelist Red Hat Brazil Compiler Engineer
