My check-gcc runs are completely dominated by the time it takes to
test compile.exp=20001226-1.c
On sparc when compiling this function at -O1 the lowest hanging fruit
is some sillyness in reorg. It is trying to test a very specific
condition within a well contained code block, but the label scanning
is not constrained properly so things go haywire for large functions.
Specifically it is looking at:
INSN SEQ (delay_insn
delay_slot_1
...)
...
NEXT
LABEL:
next_active_insn (NEXT)
and wants to scan backwards to find if LABEL exists, starting at
next_active_insn (NEXT), and if so are NEXT and delay_slot_1 equal
instructions (equal meaning rtx_equal_p()).
But it just does a blind prev_label() call which will happily scan all
the way to the beginning of the function. Compilation of this
testcase at -O1 spends 1/3 of it's time in prev_insn ().
In this specific reorg check, there is no reason to scan further back
than INSN.
So I've added a limited scanning helper function to reorg.c for this
purpose and got rid of prev_insn entirely since there are no longer
any users.
Unfortunately, at -O2 this testcase causes exponential cost problems
which are beyond my skills to fix. Specifically,
tail_merge_optimize() applies it's clusters and
iterate_fix_dominators() hits the worst case O(n) complexity of
et_splay for a CFG structured like this. :-/ %38 of the compilation
time is spent in et_splay().
Committed to trunk.
gcc/
* reorg.c (label_before_next_insn): New function.
(relax_delay_slots): Use it instead of prev_label.
* rtl.h (prev_label): Delete declaration.
* emit-rtl.c (prev_label): Remove.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@180674
138bc75d-0d04-0410-961f-82ee72b054a4
---
gcc/ChangeLog | 7 +++++++
gcc/emit-rtl.c | 15 ---------------
gcc/reorg.c | 17 ++++++++++++++++-
gcc/rtl.h | 1 -
4 files changed, 23 insertions(+), 17 deletions(-)
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 0eb34e5..e9bda2b 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2011-10-30 David S. Miller <da...@davemloft.net>
+
+ * reorg.c (label_before_next_insn): New function.
+ (relax_delay_slots): Use it instead of prev_label.
+ * rtl.h (prev_label): Delete declaration.
+ * emit-rtl.c (prev_label): Remove.
+
2011-10-30 Revital Eres <revital.e...@linaro.org>
* modulo-sched.c (generate_prolog_epilog): Mark prolog and epilog
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index 8465237..c2bc56b 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -3330,21 +3330,6 @@ next_label (rtx insn)
return insn;
}
-/* Return the last CODE_LABEL before the insn INSN, or 0 if there is none. */
-
-rtx
-prev_label (rtx insn)
-{
- while (insn)
- {
- insn = PREV_INSN (insn);
- if (insn == 0 || LABEL_P (insn))
- break;
- }
-
- return insn;
-}
-
/* Return the last label to mark the same position as LABEL. Return LABEL
itself if it is null or any return rtx. */
diff --git a/gcc/reorg.c b/gcc/reorg.c
index f77a3a0..40d73a7 100644
--- a/gcc/reorg.c
+++ b/gcc/reorg.c
@@ -3349,6 +3349,21 @@ delete_jump (rtx insn)
delete_computation (insn);
}
+static rtx
+label_before_next_insn (rtx x, rtx scan_limit)
+{
+ rtx insn = next_active_insn (x);
+ while (insn)
+ {
+ insn = PREV_INSN (insn);
+ if (insn == scan_limit || insn == NULL_RTX)
+ return NULL_RTX;
+ if (LABEL_P (insn))
+ break;
+ }
+ return insn;
+}
+
/* Once we have tried two ways to fill a delay slot, make a pass over the
code to try to improve the results and to do such things as more jump
@@ -3634,7 +3649,7 @@ relax_delay_slots (rtx first)
identical to the one in its delay slot. In this case, we can just
delete the branch and the insn in its delay slot. */
if (next && NONJUMP_INSN_P (next)
- && prev_label (next_active_insn (next)) == target_label
+ && label_before_next_insn (next, insn) == target_label
&& simplejump_p (insn)
&& XVECLEN (pat, 0) == 2
&& rtx_equal_p (PATTERN (next), PATTERN (XVECEXP (pat, 0, 1))))
diff --git a/gcc/rtl.h b/gcc/rtl.h
index 81958a5..41536be 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -1812,7 +1812,6 @@ extern rtx next_real_insn (rtx);
extern rtx prev_active_insn (rtx);
extern rtx next_active_insn (rtx);
extern int active_insn_p (const_rtx);
-extern rtx prev_label (rtx);
extern rtx next_label (rtx);
extern rtx skip_consecutive_labels (rtx);
extern rtx next_cc0_user (rtx);
--
1.7.6.401.g6a319
