[PATCH][haifa-sched] PR rtl-optimization/68236: Exit early from autoprefetcher lookahead if not in haifa sched

[Kyrill Tkachov <kyrylo dot tkachov at arm dot com>]

Hi all,

In this PR there are tons of ICEs throughout the aarch64 testsuite when compiled with -fselective-scheduling -fselective-scheduling2 --param=sched-autopref-queue-depth=10.
Admittedly that's a rare combination as we don't use selective scheduling by default on aarch64.
The problem is that after my patch to enable auto-prefetcher modelling in the scheduler for aarch64 we now call
into autopref_multipass_dfa_lookahead_guard from the aarch64 backend hook.
However, autopref_multipass_dfa_lookahead_guard only makes sense when doing normal scheduling, the necessary structs are not
setup properly otherwise. So we end up trying to access the insn_queue, which is either NULL, or contains garbage
because it has not been properly initialised from earlier.

The solution in this patch is to exit early from autopref_multipass_dfa_lookahead_guard if insn_queue is NULL.
I'm using insn_queue as an indication that we entered from haifa-sched because I couldn't see any other
variable that keeps track of which scheduling approach we're using.
Also, I needed a hunk to reset insn_queue to NULL in haifa_sched_finish so that if we run selective scheduling
after a round of normal haifa scheduling (for example after sched fusion on aarch64) we don't end up accessing
bogus memory locations from insn_queue.

With this patch a testsuite with -fselective-scheduling/-fselective-scheduling2/--param=sched-autopref-queue-depth=10
runs sanely rather than ICE'ing in almost every test.

Bootstrapped and tested in a normal configuration on arm, aarch64 and x86_64 too.

Ok for trunk?

Thanks,
Kyrill

2015-11-09  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

    PR rtl-optimization/68236
    * haifa-sched.c (autopref_multipass_dfa_lookahead_guard): Return 0
    if insn_queue doesn't exist.
    (haifa_sched_finish): Reset insn_queue to NULL.

commit f7995307c6f66bd4be3895f6cd7e5d14d30b7fe2
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Fri Nov 6 14:39:38 2015 +0000

    [haifa-sched] PR rtl-optimization/68236: Exit early from autoprefetcher lookahead if not in haifa sched

diff --git a/gcc/haifa-sched.c b/gcc/haifa-sched.c
index caadc11..a926f4d 100644
--- a/gcc/haifa-sched.c
+++ b/gcc/haifa-sched.c
@@ -5806,7 +5806,10 @@ autopref_multipass_dfa_lookahead_guard (rtx_insn *insn1, int ready_index)
 {
   int r = 0;
 
-  if (PARAM_VALUE (PARAM_SCHED_AUTOPREF_QUEUE_DEPTH) <= 0)
+  /* Exit early if the param forbids this or if we're not entering here through
+     normal haifa scheduling.  This can happen if selective scheduling is
+     explicitly enabled.  */
+  if (!insn_queue || PARAM_VALUE (PARAM_SCHED_AUTOPREF_QUEUE_DEPTH) <= 0)
     return 0;
 
   if (sched_verbose >= 2 && ready_index == 0)
@@ -7483,6 +7486,7 @@ haifa_sched_finish (void)
   sched_deps_finish ();
   sched_finish_luids ();
   current_sched_info = NULL;
+  insn_queue = NULL;
   sched_finish ();
 }