re PR tree-optimization/42438 (Fix for PR38819 is too conservative)

2010-01-03  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/42438
	* tree-ssa-pre.c (struct bb_bitmap_sets): Add
	contains_may_not_return_call flag.
	(BB_MAY_NOTRETURN): New.
	(valid_in_sets): Trapping nary operations are not valid
	in blocks that may not return.
	(insert_into_preds_of_block): Remove check for trapping
	expressions.
	(compute_avail): Compute also BB_MAY_NOTRETURN.

	* gcc.dg/tree-ssa/ssa-pre-27.c: New testcase.

From-SVN: r155584

4 files changed, 78 insertions, 11 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c133aac..8065b24 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,15 @@
+2010-01-03  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/42438
+	* tree-ssa-pre.c (struct bb_bitmap_sets): Add
+	contains_may_not_return_call flag.
+	(BB_MAY_NOTRETURN): New.
+	(valid_in_sets): Trapping nary operations are not valid
+	in blocks that may not return.
+	(insert_into_preds_of_block): Remove check for trapping
+	expressions.
+	(compute_avail): Compute also BB_MAY_NOTRETURN.
+
 2010-01-03  Gerald Pfeifer  <gerald@pfeifer.com>
 
 	* doc/invoke.texi: Add 2010 to copyright years.
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index d1580fa..609589c 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2010-01-03  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/42438
+	* gcc.dg/tree-ssa/ssa-pre-27.c: New testcase.
+
 2010-01-02  Richard Guenther  <rguenther@suse.de>
 
 	PR testsuite/41651
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-27.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-27.c
new file mode 100644
index 0000000..1d60a30
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-27.c
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-pre" } */
+
+int foo (int i, int j, int b)
+{
+  int res = 0;
+  if (b)
+    res = i/j;
+  /* We should insert the possibly trapping i/j.  */
+  res += i/j;
+  return res;
+}
+
+extern void bar (void);
+int foo2 (int i, int j, int b)
+{
+  int res = 0;
+  if (b)
+    res = i/j;
+  /* But we fail so here because of the possibly not returning
+     call in the same basic-block.  */
+  res += i/j;
+  bar ();
+  return res;
+}
+
+/* { dg-final { scan-tree-dump-times "# prephitmp" 1 "pre" } } */
+/* { dg-final { scan-tree-dump-times "# prephitmp" 2 "pre" { xfail *-*-* } } } */
+/* { dg-final { cleanup-tree-dump "pre" } } */
diff --git a/gcc/tree-ssa-pre.c b/gcc/tree-ssa-pre.c
index 52e973f..7d9b9bf 100644
--- a/gcc/tree-ssa-pre.c
+++ b/gcc/tree-ssa-pre.c
@@ -382,11 +382,14 @@ typedef struct bb_bitmap_sets
   bitmap expr_dies;
 
   /* True if we have visited this block during ANTIC calculation.  */
-  unsigned int visited:1;
+  unsigned int visited : 1;
 
   /* True we have deferred processing this block during ANTIC
      calculation until its successor is processed.  */
   unsigned int deferred : 1;
+
+  /* True when the block contains a call that might not return.  */
+  unsigned int contains_may_not_return_call : 1;
 } *bb_value_sets_t;
 
 #define EXP_GEN(BB)	((bb_value_sets_t) ((BB)->aux))->exp_gen
@@ -399,6 +402,7 @@ typedef struct bb_bitmap_sets
 #define EXPR_DIES(BB)	((bb_value_sets_t) ((BB)->aux))->expr_dies
 #define BB_VISITED(BB)	((bb_value_sets_t) ((BB)->aux))->visited
 #define BB_DEFERRED(BB) ((bb_value_sets_t) ((BB)->aux))->deferred
+#define BB_MAY_NOTRETURN(BB) ((bb_value_sets_t) ((BB)->aux))->contains_may_not_return_call
 
 
 /* Basic block list in postorder.  */
@@ -2032,6 +2036,13 @@ valid_in_sets (bitmap_set_t set1, bitmap_set_t set2, pre_expr expr,
 		  return false;
 	      }
 	  }
+	/* If the NARY may trap make sure the block does not contain
+	   a possible exit point.
+	   ???  This is overly conservative if we translate AVAIL_OUT
+	   as the available expression might be after the exit point.  */
+	if (BB_MAY_NOTRETURN (block)
+	    && vn_nary_may_trap (nary))
+	  return false;
 	return true;
       }
       break;
@@ -2469,6 +2480,7 @@ compute_antic (void)
 
       BB_VISITED (block) = 0;
       BB_DEFERRED (block) = 0;
+
       /* While we are here, give empty ANTIC_IN sets to each block.  */
       ANTIC_IN (block) = bitmap_set_new ();
       PA_IN (block) = bitmap_set_new ();
@@ -3187,16 +3199,6 @@ insert_into_preds_of_block (basic_block block, unsigned int exprnum,
 	}
     }
 
-  /* Make sure we are not inserting trapping expressions.  */
-  FOR_EACH_EDGE (pred, ei, block->preds)
-    {
-      bprime = pred->src;
-      eprime = avail[bprime->index];
-      if (eprime->kind == NARY
-	  && vn_nary_may_trap (PRE_EXPR_NARY (eprime)))
-	return false;
-    }
-
   /* Make the necessary insertions.  */
   FOR_EACH_EDGE (pred, ei, block->preds)
     {
@@ -3804,6 +3806,8 @@ compute_avail (void)
       for (gsi = gsi_start_phis (block); !gsi_end_p (gsi); gsi_next (&gsi))
 	make_values_for_phi (gsi_stmt (gsi), block);
 
+      BB_MAY_NOTRETURN (block) = 0;
+
       /* Now compute value numbers and populate value sets with all
 	 the expressions computed in BLOCK.  */
       for (gsi = gsi_start_bb (block); !gsi_end_p (gsi); gsi_next (&gsi))
@@ -3814,6 +3818,23 @@ compute_avail (void)
 	  stmt = gsi_stmt (gsi);
 	  gimple_set_uid (stmt, stmt_uid++);
 
+	  /* Cache whether the basic-block has any non-visible side-effect
+	     or control flow.
+	     If this isn't a call or it is the last stmt in the
+	     basic-block then the CFG represents things correctly.  */
+	  if (is_gimple_call (stmt)
+	      && !stmt_ends_bb_p (stmt))
+	    {
+	      /* Non-looping const functions always return normally.
+		 Otherwise the call might not return or have side-effects
+		 that forbids hoisting possibly trapping expressions
+		 before it.  */
+	      int flags = gimple_call_flags (stmt);
+	      if (!(flags & ECF_CONST)
+		  || (flags & ECF_LOOPING_CONST_OR_PURE))
+		BB_MAY_NOTRETURN (block) = 1;
+	    }
+
 	  FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_DEF)
 	    {
 	      pre_expr e = get_or_alloc_expr_for_name (op);