From: Aldy Hernandez <aldyh@redhat.com>
Date: Tue, 28 Sep 2021 08:19:57 +0000 (+0200)
Subject: Improve jump threading dump output.
X-Git-Tag: basepoints/gcc-13~4385
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0400ca17f361dcc7f8230bb69a25de22497c73c3;p=thirdparty%2Fgcc.git

Improve jump threading dump output.

In analyzing PR102511, it has become abundantly clear that we need
better debugging aids for the jump threader solver.  Currently
debugging these issues is a nightmare if you're not intimately
familiar with the code.  This patch attempts to improve this.

First, I'm enabling path solver dumps with TDF_THREADING.  None of the
available TDF_* flags are a good match, and using TDF_DETAILS would blow
up the dump file, since both threaders continually call the solver to
try out candidates.  This will allow dumping path solver details without
having to resort to hacking the source.

I am also dumping the current registered_jump_thread dbg counter used
by the registry, in the solver.  That way narrowing down a problematic
thread can then be examined by -fdump-*-threading and looking at the
solver details surrounding the appropriate counter (which the dbgcnt
also dumps to the dump file).

You still need knowledge of the solver to debug these issues, but at
least now it's not entirely opaque.

Tested on x86-64 Linux.

gcc/ChangeLog:

	* dbgcnt.c (dbg_cnt_counter): New.
	* dbgcnt.h (dbg_cnt_counter): New.
	* dumpfile.c (dump_options): Add entry for TDF_THREADING.
	* dumpfile.h (enum dump_flag): Add TDF_THREADING.
	* gimple-range-path.cc (DEBUG_SOLVER): Use TDF_THREADING.
	* tree-ssa-threadupdate.c (dump_jump_thread_path): Dump out
	debug counter.
---

diff --git a/gcc/dbgcnt.c b/gcc/dbgcnt.c
index 934bbe033eeb..6a7eb34cd3ed 100644
--- a/gcc/dbgcnt.c
+++ b/gcc/dbgcnt.c
@@ -98,6 +98,14 @@ dbg_cnt (enum debug_counter index)
     return false;
 }
 
+/* Return the counter for INDEX.  */
+
+unsigned
+dbg_cnt_counter (enum debug_counter index)
+{
+  return count[index];
+}
+
 /* Compare limit_tuple intervals by first item in descending order.  */
 
 static int
diff --git a/gcc/dbgcnt.h b/gcc/dbgcnt.h
index 17f2091f5a72..3c35dcc3e0a7 100644
--- a/gcc/dbgcnt.h
+++ b/gcc/dbgcnt.h
@@ -33,6 +33,7 @@ enum debug_counter {
 
 extern bool dbg_cnt_is_enabled (enum debug_counter index);
 extern bool dbg_cnt (enum debug_counter index);
+extern unsigned dbg_cnt_counter (enum debug_counter index);
 extern void dbg_cnt_process_opt (const char *arg);
 extern void dbg_cnt_list_all_counters (void);
 
diff --git a/gcc/dumpfile.c b/gcc/dumpfile.c
index 8169daf7f596..e6ead5debe56 100644
--- a/gcc/dumpfile.c
+++ b/gcc/dumpfile.c
@@ -145,6 +145,7 @@ static const kv_pair<dump_flags_t> dump_options[] =
   {"missed", MSG_MISSED_OPTIMIZATION},
   {"note", MSG_NOTE},
   {"optall", MSG_ALL_KINDS},
+  {"threading", TDF_THREADING},
   {"all", dump_flags_t (TDF_ALL_VALUES
 			& ~(TDF_RAW | TDF_SLIM | TDF_LINENO | TDF_GRAPH
 			    | TDF_STMTADDR | TDF_RHS_ONLY | TDF_NOUID
diff --git a/gcc/dumpfile.h b/gcc/dumpfile.h
index 892bfc9ae90b..6c7758dd2fb6 100644
--- a/gcc/dumpfile.h
+++ b/gcc/dumpfile.h
@@ -197,6 +197,9 @@ enum dump_flag
   /* For error.  */
   TDF_ERROR = (1 << 26),
 
+  /* Dumping for range path solver.  */
+  TDF_THREADING = (1 << 27),
+
   /* All values.  */
   TDF_ALL_VALUES = (1 << 29) - 1
 };
diff --git a/gcc/gimple-range-path.cc b/gcc/gimple-range-path.cc
index 9da67d2a35be..a29d5318ca9b 100644
--- a/gcc/gimple-range-path.cc
+++ b/gcc/gimple-range-path.cc
@@ -34,7 +34,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-iterator.h"
 
 // Internal construct to help facilitate debugging of solver.
-#define DEBUG_SOLVER (0 && dump_file)
+#define DEBUG_SOLVER (dump_file && dump_flags & TDF_THREADING)
 
 path_range_query::path_range_query (gimple_ranger &ranger, bool resolve)
   : m_ranger (ranger)
diff --git a/gcc/tree-ssa-threadupdate.c b/gcc/tree-ssa-threadupdate.c
index 71e602ffa2da..dcabfdb30d2c 100644
--- a/gcc/tree-ssa-threadupdate.c
+++ b/gcc/tree-ssa-threadupdate.c
@@ -218,10 +218,15 @@ dump_jump_thread_path (FILE *dump_file,
 		       const vec<jump_thread_edge *> &path,
 		       bool registering)
 {
-  fprintf (dump_file,
-	   "  %s jump thread: (%d, %d) incoming edge; ",
-	   (registering ? "Registering" : "Cancelling"),
-	   path[0]->e->src->index, path[0]->e->dest->index);
+  if (registering)
+    fprintf (dump_file,
+	     "  [%u] Registering jump thread: (%d, %d) incoming edge; ",
+	     dbg_cnt_counter (registered_jump_thread),
+	     path[0]->e->src->index, path[0]->e->dest->index);
+  else
+    fprintf (dump_file,
+	     "  Cancelling jump thread: (%d, %d) incoming edge; ",
+	     path[0]->e->src->index, path[0]->e->dest->index);
 
   for (unsigned int i = 1; i < path.length (); i++)
     {