Quoting Richard Sandiford <rdsandif...@googlemail.com>:
Joern Rennecke <joern.renne...@embecosm.com> writes:
When the condition is not fulfilled, we want to keep the length from the
previous iteration.
Right, that's what I mean. So we need to make sure that the difference
between the address of the current instruction and the address of the
next instruction also doesn't change. The code as posted was:
else
{
new_length = insn_current_length (insn);
insn_current_address += new_length;
}
#ifdef ADJUST_INSN_LENGTH
/* If needed, do any adjustment. */
tmp_length = new_length;
ADJUST_INSN_LENGTH (insn, new_length);
insn_current_address += (new_length - tmp_length);
#endif
if (new_length != insn_lengths[uid]
&& (new_length > insn_lengths[uid] || first_pass))
{
insn_lengths[uid] = new_length;
something_changed = 1;
}
which always leaves insn_current_address based off new_length,
even if new_length is out of kilter with insn_lengths[uid].
Indeed.
I have attached a patch which I believe addresses the issues you raised.
Because making the length sticky is problematic when UIDs aren't unique,
I have tested this patch on top of that patch:
http://gcc.gnu.org/ml/gcc-patches/2012-10/msg01806.html
regression tested on i686-pc-linux-gnu X cris-elf and
i686-pc-linux-gnu X mipsel-elf.
2012-10-19 J"orn Rennecke <joern.renne...@arc.com>
* final.c (shorten_branches): When optimizing, start with small
length and increase from there, and don't decrease lengths.
Index: final.c
===================================================================
--- final.c (revision 192573)
+++ final.c (working copy)
@@ -1066,7 +1066,15 @@ shorten_branches (rtx first ATTRIBUTE_UN
}
#endif /* CASE_VECTOR_SHORTEN_MODE */
+ /* When optimizing, we start assuming minimum length, and keep increasing
+ lengths as we find the need for this, till nothing changes.
+ When not optimizing, we start assuming maximum lengths, and
+ do a single pass to update the lengths. */
+ bool increasing = optimize != 0;
+
/* Compute initial lengths, addresses, and varying flags for each insn. */
+ int (*length_fun) (rtx) = increasing ? insn_min_length : insn_default_length;
+
for (insn_current_address = 0, insn = first;
insn != 0;
insn_current_address += insn_lengths[uid], insn = NEXT_INSN (insn))
@@ -1117,6 +1125,8 @@ shorten_branches (rtx first ATTRIBUTE_UN
#else
const_delay_slots = 0;
#endif
+ int (*inner_length_fun) (rtx)
+ = const_delay_slots ? length_fun : insn_default_length;
/* Inside a delay slot sequence, we do not do any branch shortening
if the shortening could change the number of delay slots
of the branch. */
@@ -1131,7 +1141,7 @@ shorten_branches (rtx first ATTRIBUTE_UN
inner_length = (asm_insn_count (PATTERN (inner_insn))
* insn_default_length (inner_insn));
else
- inner_length = insn_default_length (inner_insn);
+ inner_length = inner_length_fun (inner_insn);
insn_lengths[inner_uid] = inner_length;
if (const_delay_slots)
@@ -1149,7 +1159,7 @@ shorten_branches (rtx first ATTRIBUTE_UN
}
else if (GET_CODE (body) != USE && GET_CODE (body) != CLOBBER)
{
- insn_lengths[uid] = insn_default_length (insn);
+ insn_lengths[uid] = length_fun (insn);
varying_length[uid] = insn_variable_length_p (insn);
}
@@ -1165,6 +1175,7 @@ shorten_branches (rtx first ATTRIBUTE_UN
get the current insn length. If it has changed, reflect the change.
When nothing changes for a full pass, we are done. */
+ bool first_pass ATTRIBUTE_UNUSED = true;
while (something_changed)
{
something_changed = 0;
@@ -1220,6 +1231,7 @@ shorten_branches (rtx first ATTRIBUTE_UN
rtx prev;
int rel_align = 0;
addr_diff_vec_flags flags;
+ enum machine_mode vec_mode;
/* Avoid automatic aggregate initialization. */
flags = ADDR_DIFF_VEC_FLAGS (body);
@@ -1298,9 +1310,12 @@ shorten_branches (rtx first ATTRIBUTE_UN
else
max_addr += align_fuzz (max_lab, rel_lab, 0, 0);
}
- PUT_MODE (body, CASE_VECTOR_SHORTEN_MODE (min_addr - rel_addr,
- max_addr - rel_addr,
- body));
+ vec_mode = CASE_VECTOR_SHORTEN_MODE (min_addr - rel_addr,
+ max_addr - rel_addr, body);
+ if (first_pass
+ || (GET_MODE_SIZE (vec_mode)
+ >= GET_MODE_SIZE (GET_MODE (body))))
+ PUT_MODE (body, vec_mode);
if (JUMP_TABLES_IN_TEXT_SECTION
|| readonly_data_section == text_section)
{
@@ -1362,10 +1377,15 @@ shorten_branches (rtx first ATTRIBUTE_UN
if (inner_length != insn_lengths[inner_uid])
{
- insn_lengths[inner_uid] = inner_length;
- something_changed = 1;
+ if (!increasing || inner_length > insn_lengths[inner_uid])
+ {
+ insn_lengths[inner_uid] = inner_length;
+ something_changed = 1;
+ }
+ else
+ inner_length = insn_lengths[inner_uid];
}
- insn_current_address += insn_lengths[inner_uid];
+ insn_current_address += inner_length;
new_length += inner_length;
}
}
@@ -1382,15 +1402,19 @@ shorten_branches (rtx first ATTRIBUTE_UN
insn_current_address += (new_length - tmp_length);
#endif
- if (new_length != insn_lengths[uid])
+ if (new_length != insn_lengths[uid]
+ && (!increasing || new_length > insn_lengths[uid]))
{
insn_lengths[uid] = new_length;
something_changed = 1;
}
+ else
+ insn_current_address += insn_lengths[uid] - new_length;
}
/* For a non-optimizing compile, do only a single pass. */
- if (!optimize)
+ if (!increasing)
break;
+ first_pass = false;
}
free (varying_length);
