re PR middle-end/34450 (compile takes up 1.8 GB RAM at -O1)

2007-12-13  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/34450
	* params.def (PARAM_SCCVN_MAX_SCC_SIZE): New param.
	* invoke.texi (sccvn-max-scc-size): Document.
	* Makefile.in (tree-ssa-sccvn.o): Add $(PARAMS_H) dependency.
	* tree-ssa-sccvn.h (run_scc_vn): Return true on success, false
	on error.
	* tree-ssa-sccvn.c (params.h): Include.
	(DFS): Return true if all went well, return false as soon as
	a SCC exceeds the size of PARAM_SCCVN_MAX_SCC_SIZE.
	(run_scc_vn): Return true if all went well, return false if
	we aborted during DFS.
	* tree-ssa-pre.c (execute_pre): Check if SCCVN finished
	successfully, otherwise bail out.

From-SVN: r130895

gcc/ChangeLog

@@ -1,3 +1,19 @@
+2007-12-13  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/34450
+	* params.def (PARAM_SCCVN_MAX_SCC_SIZE): New param.
+	* invoke.texi (sccvn-max-scc-size): Document.
+	* Makefile.in (tree-ssa-sccvn.o): Add $(PARAMS_H) dependency.
+	* tree-ssa-sccvn.h (run_scc_vn): Return true on success, false
+	on error.
+	* tree-ssa-sccvn.c (params.h): Include.
+	(DFS): Return true if all went well, return false as soon as
+	a SCC exceeds the size of PARAM_SCCVN_MAX_SCC_SIZE.
+	(run_scc_vn): Return true if all went well, return false if
+	we aborted during DFS.
+	* tree-ssa-pre.c (execute_pre): Check if SCCVN finished
+	successfully, otherwise bail out.
+
 2007-12-13  Olga Golovanevsky  <olga@il.ibm.com>
 
 	* ipa-struct-reorg.c (is_candidate): Print information to dump 

gcc/Makefile.in

@@ -2075,7 +2075,8 @@ tree-ssa-sccvn.o : tree-ssa-sccvn.c $(TREE_FLOW_H) $(CONFIG_H) \
    $(SYSTEM_H) $(TREE_H) $(GGC_H) $(DIAGNOSTIC_H) $(TIMEVAR_H) \
    $(TM_H) coretypes.h $(TREE_DUMP_H) tree-pass.h $(FLAGS_H) $(CFGLOOP_H) \
    alloc-pool.h $(BASIC_BLOCK_H) bitmap.h $(HASHTAB_H) $(TREE_GIMPLE_H) \
-   $(TREE_INLINE_H) tree-iterator.h tree-ssa-propagate.h tree-ssa-sccvn.h
+   $(TREE_INLINE_H) tree-iterator.h tree-ssa-propagate.h tree-ssa-sccvn.h \
+   $(PARAMS_H)
 tree-vn.o : tree-vn.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(GGC_H) \
    $(TREE_H) $(TREE_FLOW_H) $(HASHTAB_H) langhooks.h tree-pass.h \
    $(TREE_DUMP_H) $(DIAGNOSTIC_H) tree-ssa-sccvn.h

gcc/doc/invoke.texi

@@ -7182,6 +7182,12 @@ parameter sets a limit on the length of the sets that are computed,
 which prevents the runaway behaviour.  Setting a value of 0 for
 this paramter will allow an unlimited set length.
 
+@item sccvn-max-scc-size
+Maximum size of a strongly connected component (SCC) during SCCVN
+processing.  If this limit is hit, SCCVN processing for the whole
+function will not be done and optimizations depending on it will
+be disabled.  The default maximum SCC size is 10000.
+
 @end table
 @end table
 

gcc/params.def

@@ -713,6 +713,17 @@ DEFPARAM (PARAM_MAX_PARTIAL_ANTIC_LENGTH,
 	  "Maximum length of partial antic set when performing tree pre optimization",
 	  100, 0, 0)
 
+/* The following is used as a stop-gap limit for cases where really huge
+   SCCs blow up memory and compile-time use too much.  If we hit this limit,
+   SCCVN and such FRE and PRE will be not done at all for the current
+   function.  */
+
+DEFPARAM (PARAM_SCCVN_MAX_SCC_SIZE,
+	  "sccvn-max-scc-size",
+	  "Maximum size of a SCC before SCCVN stops processing a function",
+	  10000, 10, 0)
+
+
 /*
 Local variables:
 mode:c

gcc/tree-ssa-pre.c

@@ -3933,7 +3933,13 @@ execute_pre (bool do_fre)
     insert_fake_stores ();
 
   /* Collect and value number expressions computed in each basic block.  */
-  run_scc_vn ();
+  if (!run_scc_vn ())
+    {
+      if (!do_fre)
+	remove_dead_inserted_code ();
+      fini_pre ();
+      return;
+    }
   switch_to_PRE_table ();
   compute_avail ();
 

gcc/tree-ssa-sccvn.c

@@ -42,6 +42,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "bitmap.h"
 #include "langhooks.h"
 #include "cfgloop.h"
+#include "params.h"
 #include "tree-ssa-propagate.h"
 #include "tree-ssa-sccvn.h"
 
@@ -1837,9 +1838,11 @@ process_scc (VEC (tree, heap) *scc)
 /* Depth first search on NAME to discover and process SCC's in the SSA
    graph.
    Execution of this algorithm relies on the fact that the SCC's are
-   popped off the stack in topological order.  */
+   popped off the stack in topological order.
+   Returns true if successful, false if we stopped processing SCC's due
+   to ressource constraints.  */
 
-static void
+static bool
 DFS (tree name)
 {
   ssa_op_iter iter;
@@ -1870,7 +1873,8 @@ DFS (tree name)
 
 	  if (! (VN_INFO (use)->visited))
 	    {
-	      DFS (use);
+	      if (!DFS (use))
+		return false;
 	      VN_INFO (name)->low = MIN (VN_INFO (name)->low,
 					 VN_INFO (use)->low);
 	    }
@@ -1899,6 +1903,17 @@ DFS (tree name)
 	  VEC_safe_push (tree, heap, scc, x);
 	} while (x != name);
 
+      /* Bail out of SCCVN in case a SCC turns out to be incredibly large.  */
+      if (VEC_length (tree, scc)
+	    > (unsigned)PARAM_VALUE (PARAM_SCCVN_MAX_SCC_SIZE))
+	{
+	  if (dump_file)
+	    fprintf (dump_file, "WARNING: Giving up with SCCVN due to "
+		     "SCC size %u exceeding %u\n", VEC_length (tree, scc),
+		     (unsigned)PARAM_VALUE (PARAM_SCCVN_MAX_SCC_SIZE));
+	  return false;
+	}
+
       if (VEC_length (tree, scc) > 1)
 	sort_scc (scc);
 
@@ -1909,6 +1924,8 @@ DFS (tree name)
 
       VEC_free (tree, heap, scc);
     }
+
+  return true;
 }
 
 static void
@@ -2074,7 +2091,10 @@ free_scc_vn (void)
     }
 }
 
-void
+/* Do SCCVN.  Returns true if it finished, false if we bailed out
+   due to ressource constraints.  */
+
+bool
 run_scc_vn (void)
 {
   size_t i;
@@ -2100,7 +2120,11 @@ run_scc_vn (void)
       if (name
 	  && VN_INFO (name)->visited == false
 	  && !has_zero_uses (name))
-	DFS (name);
+	if (!DFS (name))
+	  {
+	    free_scc_vn ();
+	    return false;
+	  }
     }
 
   if (dump_file && (dump_flags & TDF_DETAILS))
@@ -2123,4 +2147,6 @@ run_scc_vn (void)
 	    }
 	}
     }
+
+  return true;
 }

gcc/tree-ssa-sccvn.h

@@ -48,7 +48,7 @@ typedef struct vn_ssa_aux
 /* Return the value numbering info for an SSA_NAME.  */
 extern vn_ssa_aux_t VN_INFO (tree);
 extern vn_ssa_aux_t VN_INFO_GET (tree);
-void run_scc_vn (void);
+bool run_scc_vn (void);
 void free_scc_vn (void);
 void switch_to_PRE_table (void);
 tree vn_binary_op_lookup (tree);