re PR tree-optimization/71866 (gcc locks up after fix for PR70159)

2016-07-14  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/71866
	* tree-ssa-pre.c (get_constant_for_value_id): Remove.
	(do_hoist_insertion): Avoid endless recursion when we
	didn't insert anything because we managed to simplify
	things down to a constant or SSA name.
	(fully_constant_expression): Re-write in terms of ...
	* tree-ssa-sccvn.h (vn_nary_simplify): ... this.  Declare.
	* tree-ssa-sccvn.c (vn_nary_simplify): New wrapper around
	vn_nary_build_or_lookup_1.
	(vn_nary_build_or_lookup_1): Added flag and renamed from ...
	(vn_nary_build_or_lookup): ... this which now wraps it.

	* gcc.dg/torture/pr71866.c: New testcase.

From-SVN: r238334

1 files changed, 21 insertions, 96 deletions

diff --git a/gcc/tree-ssa-pre.c b/gcc/tree-ssa-pre.c
index a5f3f71..518346a 100644
--- a/gcc/tree-ssa-pre.c
+++ b/gcc/tree-ssa-pre.c
@@ -1164,29 +1164,6 @@ get_or_alloc_expr_for_constant (tree constant)
   return newexpr;
 }
 
-/* Given a value id V, find the actual tree representing the constant
-   value if there is one, and return it. Return NULL if we can't find
-   a constant.  */
-
-static tree
-get_constant_for_value_id (unsigned int v)
-{
-  if (value_id_constant_p (v))
-    {
-      unsigned int i;
-      bitmap_iterator bi;
-      bitmap exprset = value_expressions[v];
-
-      EXECUTE_IF_SET_IN_BITMAP (exprset, 0, i, bi)
-	{
-	  pre_expr expr = expression_for_id (i);
-	  if (expr->kind == CONSTANT)
-	    return PRE_EXPR_CONSTANT (expr);
-	}
-    }
-  return NULL;
-}
-
 /* Get or allocate a pre_expr for a piece of GIMPLE, and return it.
    Currently only supports constants and SSA_NAMES.  */
 static pre_expr
@@ -1236,76 +1213,16 @@ fully_constant_expression (pre_expr e)
     case NARY:
       {
 	vn_nary_op_t nary = PRE_EXPR_NARY (e);
-	switch (TREE_CODE_CLASS (nary->opcode))
-	  {
-	  case tcc_binary:
-	  case tcc_comparison:
-	    {
-	      /* We have to go from trees to pre exprs to value ids to
-		 constants.  */
-	      tree naryop0 = nary->op[0];
-	      tree naryop1 = nary->op[1];
-	      tree result;
-	      if (!is_gimple_min_invariant (naryop0))
-		{
-		  pre_expr rep0 = get_or_alloc_expr_for (naryop0);
-		  unsigned int vrep0 = get_expr_value_id (rep0);
-		  tree const0 = get_constant_for_value_id (vrep0);
-		  if (const0)
-		    naryop0 = fold_convert (TREE_TYPE (naryop0), const0);
-		}
-	      if (!is_gimple_min_invariant (naryop1))
-		{
-		  pre_expr rep1 = get_or_alloc_expr_for (naryop1);
-		  unsigned int vrep1 = get_expr_value_id (rep1);
-		  tree const1 = get_constant_for_value_id (vrep1);
-		  if (const1)
-		    naryop1 = fold_convert (TREE_TYPE (naryop1), const1);
-		}
-	      result = fold_binary (nary->opcode, nary->type,
-				    naryop0, naryop1);
-	      if (result && is_gimple_min_invariant (result))
-		return get_or_alloc_expr_for_constant (result);
-	      /* We might have simplified the expression to a
-		 SSA_NAME for example from x_1 * 1.  But we cannot
-		 insert a PHI for x_1 unconditionally as x_1 might
-		 not be available readily.  */
-	      return e;
-	    }
-	  case tcc_reference:
-	    if (nary->opcode != REALPART_EXPR
-		&& nary->opcode != IMAGPART_EXPR
-		&& nary->opcode != VIEW_CONVERT_EXPR)
-	      return e;
-	    /* Fallthrough.  */
-	  case tcc_unary:
-	    {
-	      /* We have to go from trees to pre exprs to value ids to
-		 constants.  */
-	      tree naryop0 = nary->op[0];
-	      tree const0, result;
-	      if (is_gimple_min_invariant (naryop0))
-		const0 = naryop0;
-	      else
-		{
-		  pre_expr rep0 = get_or_alloc_expr_for (naryop0);
-		  unsigned int vrep0 = get_expr_value_id (rep0);
-		  const0 = get_constant_for_value_id (vrep0);
-		}
-	      result = NULL;
-	      if (const0)
-		{
-		  tree type1 = TREE_TYPE (nary->op[0]);
-		  const0 = fold_convert (type1, const0);
-		  result = fold_unary (nary->opcode, nary->type, const0);
-		}
-	      if (result && is_gimple_min_invariant (result))
-		return get_or_alloc_expr_for_constant (result);
-	      return e;
-	    }
-	  default:
-	    return e;
-	  }
+	tree res = vn_nary_simplify (nary);
+	if (!res)
+	  return e;
+	if (is_gimple_min_invariant (res))
+	  return get_or_alloc_expr_for_constant (res);
+	/* We might have simplified the expression to a
+	   SSA_NAME for example from x_1 * 1.  But we cannot
+	   insert a PHI for x_1 unconditionally as x_1 might
+	   not be available readily.  */
+	return e;
       }
     case REFERENCE:
       {
@@ -3618,10 +3535,18 @@ do_hoist_insertion (basic_block block)
       gimple_seq stmts = NULL;
       tree res = create_expression_by_pieces (block, expr, &stmts,
 					      get_expr_type (expr));
-      if (gsi_end_p (last) || is_ctrl_stmt (gsi_stmt (last)))
-	gsi_insert_seq_before (&last, stmts, GSI_SAME_STMT);
+
+      /* Do not return true if expression creation ultimately
+         did not insert any statements.  */
+      if (gimple_seq_empty_p (stmts))
+	res = NULL_TREE;
       else
-	gsi_insert_seq_after (&last, stmts, GSI_NEW_STMT);
+	{
+	  if (gsi_end_p (last) || is_ctrl_stmt (gsi_stmt (last)))
+	    gsi_insert_seq_before (&last, stmts, GSI_SAME_STMT);
+	  else
+	    gsi_insert_seq_after (&last, stmts, GSI_NEW_STMT);
+	}
 
       /* Make sure to not return true if expression creation ultimately
          failed but also make sure to insert any stmts produced as they