[PATCH][tree-optimization/59597] Reinstate code to cancel some jump threads

Jeff Law law@redhat.com
Wed Jan 22 21:28:00 GMT 2014


I had taken this code out as the original cases I'd encountered were 
better handled by reorganization the order in which we thread blocks.

However, as seen in 59597, there's still clearly cases where a jump 
threading path with a joiner block can have a threaded subpath. 
Threading the joiner block in this case is just wasteful (compile-time, 
memory consumption, code bloat) and as seen in 59597 can inhibit 
optimizations and result in significant performance degradations.

So this brings that code back with some improvements in the debugging 
dumps so we can see when it happens.  It should restore the performance 
of the sample code in 59597 back to where we were a while ago.

Bootstrapped & regression tested on x86_64-unknown-linux-gnu, confirmed 
the testcase's runtime is dramatically improved as well.  Installed on 
the trunk.

Jeff
-------------- next part --------------
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index bcbb7dd..ea08f1f 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,14 @@
+2014-01-22  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/59597
+	* tree-ssa-threadupdate.c (dump_jump_thread_path): Move to earlier
+	in file.  Accept new argument REGISTERING and use it to modify
+	dump output appropriately.
+	(register_jump_thread): Corresponding changes.
+	(mark_threaded_blocks): Reinstate code to cancel unprofitable
+	thread paths involving joiner blocks.  Add code to dump cancelled
+	jump threading paths.
+
 2014-01-21  Vladimir Makarov  <vmakarov@redhat.com>
 
 	PR rtl-optimization/59896
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 447d3c7..b7d7ce3 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2014-01-22  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/59597
+	* gcc.dg/tree-ssa/pr59597.c: New test.
+
 2014-01-22  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
 
 	* gcc.dg/vmx/insert-vsx-be-order.c: New.
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr59597.c b/gcc/testsuite/gcc.dg/tree-ssa/pr59597.c
new file mode 100644
index 0000000..814d299
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr59597.c
@@ -0,0 +1,55 @@
+/* { dg-do compile } */
+/* { dg-options "-Ofast -fdump-tree-vrp1-details" } */
+
+typedef unsigned short u16;
+typedef unsigned char u8;
+typedef unsigned int u32;
+#define NNN 10
+
+u32 f[NNN], t[NNN];
+
+u16 Calc_crc8(u8 data, u16 crc )
+{
+  u8 i=0,x16=0,carry=0;
+  for (i = 0; i < 8; i++)
+    {
+      x16 = (u8)((data & 1) ^ ((u8)crc & 1));
+      data >>= 1;
+ 
+      if (x16 == 1)
+	{
+	  crc ^= 0x4002;
+	  carry = 1;
+	}
+      else
+	carry = 0;
+      crc >>= 1;
+      if (carry)
+	crc |= 0x8000;
+      else
+	crc &= 0x7fff;
+    }
+  return crc;
+}
+int main (int argc, char argv[])
+{
+  int i, j; u16 crc;
+  for (j = 0; j < 10000000; j++)
+    {
+      for (i = 0; i < NNN; i++)
+	{
+	  f[i] = random(i);
+	  t[i] = random(NNN - i - 1);
+	}
+      for (i=0; i<NNN; i++) 
+	{
+	  crc=Calc_crc8(f[i],(u16)argc);
+	  crc=Calc_crc8(t[i],crc);
+	}
+    }
+  return crc;
+}
+
+/* { dg-final { scan-tree-dump "Cancelling" "vrp1" } } */
+/* { dg-final { cleanup-tree-dump "vrp1" } } */
+
diff --git a/gcc/tree-ssa-threadupdate.c b/gcc/tree-ssa-threadupdate.c
index c0476b4..f458d6a 100644
--- a/gcc/tree-ssa-threadupdate.c
+++ b/gcc/tree-ssa-threadupdate.c
@@ -148,6 +148,40 @@ struct redirection_data : typed_free_remove<redirection_data>
   static inline int equal (const value_type *, const compare_type *);
 };
 
+/* Dump a jump threading path, including annotations about each
+   edge in the path.  */
+
+static void
+dump_jump_thread_path (FILE *dump_file, 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);
+
+  for (unsigned int i = 1; i < path.length (); i++)
+    {
+      /* We can get paths with a NULL edge when the final destination
+	 of a jump thread turns out to be a constant address.  We dump
+	 those paths when debugging, so we have to be prepared for that
+	 possibility here.  */
+      if (path[i]->e == NULL)
+	continue;
+
+      if (path[i]->type == EDGE_COPY_SRC_JOINER_BLOCK)
+	fprintf (dump_file, " (%d, %d) joiner; ",
+		 path[i]->e->src->index, path[i]->e->dest->index);
+      if (path[i]->type == EDGE_COPY_SRC_BLOCK)
+       fprintf (dump_file, " (%d, %d) normal;",
+		 path[i]->e->src->index, path[i]->e->dest->index);
+      if (path[i]->type == EDGE_NO_COPY_SRC_BLOCK)
+       fprintf (dump_file, " (%d, %d) nocopy;",
+		 path[i]->e->src->index, path[i]->e->dest->index);
+    }
+  fputc ('\n', dump_file);
+}
+
 /* Simple hashing function.  For any given incoming edge E, we're going
    to be most concerned with the final destination of its jump thread
    path.  So hash on the block index of the final edge in the path.  */
@@ -1394,16 +1428,61 @@ mark_threaded_blocks (bitmap threaded_blocks)
   edge e;
   edge_iterator ei;
 
-  /* Move the jump threading requests from PATHS to each edge
-     which starts a jump thread path.  */
+  /* It is possible to have jump threads in which one is a subpath
+     of the other.  ie, (A, B), (B, C), (C, D) where B is a joiner
+     block and (B, C), (C, D) where no joiner block exists.
+
+     When this occurs ignore the jump thread request with the joiner
+     block.  It's totally subsumed by the simpler jump thread request.
+
+     This results in less block copying, simpler CFGs.  More importantly,
+     when we duplicate the joiner block, B, in this case we will create
+     a new threading opportunity that we wouldn't be able to optimize
+     until the next jump threading iteration.
+
+     So first convert the jump thread requests which do not require a
+     joiner block.  */
   for (i = 0; i < paths.length (); i++)
     {
       vec<jump_thread_edge *> *path = paths[i];
-      edge e = (*path)[0]->e;
-      e->aux = (void *)path;
-      bitmap_set_bit (tmp, e->dest->index);
+
+      if ((*path)[1]->type != EDGE_COPY_SRC_JOINER_BLOCK)
+	{
+	  edge e = (*path)[0]->e;
+	  e->aux = (void *)path;
+	  bitmap_set_bit (tmp, e->dest->index);
+	}
     }
 
+  /* Now iterate again, converting cases where we want to thread
+     through a joiner block, but only if no other edge on the path
+     already has a jump thread attached to it.  */
+  for (i = 0; i < paths.length (); i++)
+    {
+      vec<jump_thread_edge *> *path = paths[i];
+
+      if ((*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK)
+	{
+	  unsigned int j;
+
+	  for (j = 0; j < path->length (); j++)
+	    if ((*path)[j]->e->aux != NULL)
+	      break;
+
+	  /* If we iterated through the entire path without exiting the loop,
+	     then we are good to go, attach the path to the starting edge.  */
+	  if (j == path->length ())
+	    {
+	      edge e = (*path)[0]->e;
+	      e->aux = path;
+	      bitmap_set_bit (tmp, e->dest->index);
+	    }
+	  else if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      dump_jump_thread_path (dump_file, *path, false);
+	    }
+	}
+    }
 
 
   /* If optimizing for size, only thread through block if we don't have
@@ -1712,38 +1791,6 @@ delete_jump_thread_path (vec<jump_thread_edge *> *path)
   path->release();
 }
 
-/* Dump a jump threading path, including annotations about each
-   edge in the path.  */
-
-static void
-dump_jump_thread_path (FILE *dump_file, vec<jump_thread_edge *> path)
-{
-  fprintf (dump_file,
-	   "  Registering 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++)
-    {
-      /* We can get paths with a NULL edge when the final destination
-	 of a jump thread turns out to be a constant address.  We dump
-	 those paths when debugging, so we have to be prepared for that
-	 possibility here.  */
-      if (path[i]->e == NULL)
-	continue;
-
-      if (path[i]->type == EDGE_COPY_SRC_JOINER_BLOCK)
-	fprintf (dump_file, " (%d, %d) joiner; ",
-		 path[i]->e->src->index, path[i]->e->dest->index);
-      if (path[i]->type == EDGE_COPY_SRC_BLOCK)
-       fprintf (dump_file, " (%d, %d) normal;",
-		 path[i]->e->src->index, path[i]->e->dest->index);
-      if (path[i]->type == EDGE_NO_COPY_SRC_BLOCK)
-       fprintf (dump_file, " (%d, %d) nocopy;",
-		 path[i]->e->src->index, path[i]->e->dest->index);
-    }
-  fputc ('\n', dump_file);
-}
-
 /* Register a jump threading opportunity.  We queue up all the jump
    threading opportunities discovered by a pass and update the CFG
    and SSA form all at once.
@@ -1770,7 +1817,7 @@ register_jump_thread (vec<jump_thread_edge *> *path)
 	  {
 	    fprintf (dump_file,
 		     "Found NULL edge in jump threading path.  Cancelling jump thread:\n");
-	    dump_jump_thread_path (dump_file, *path);
+	    dump_jump_thread_path (dump_file, *path, false);
 	  }
 
 	delete_jump_thread_path (path);
@@ -1778,7 +1825,7 @@ register_jump_thread (vec<jump_thread_edge *> *path)
       }
 
   if (dump_file && (dump_flags & TDF_DETAILS))
-    dump_jump_thread_path (dump_file, *path);
+    dump_jump_thread_path (dump_file, *path, true);
 
   if (!paths.exists ())
     paths.create (5);


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