re PR tree-optimization/46726 (x*x has different cost than pow(x,2) with -ffast-math)

2010-12-07  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/46726
	* tree-inline.c (estimate_num_insns): Special case pow (x, 2.0).

From-SVN: r167531

gcc/ChangeLog

 2010-12-07  Richard Guenther  <rguenther@suse.de>
 
+	PR tree-optimization/46726
+	* tree-inline.c (estimate_num_insns): Special case pow (x, 2.0).
+
+2010-12-07  Richard Guenther  <rguenther@suse.de>
+
 	* tree-ssa-math-opts.c (execute_optimize_widening_mul): Unlink
 	virtual operands.
 

gcc/tree-inline.c

@@ -3496,16 +3496,37 @@ estimate_num_insns (gimple stmt, eni_weights *weights)
 	/* Do not special case builtins where we see the body.
 	   This just confuse inliner.  */
 	if (!decl || cgraph_node (decl)->analyzed)
-	  cost = weights->call_cost;
+	  ;
 	/* For buitins that are likely expanded to nothing or
 	   inlined do not account operand costs.  */
 	else if (is_simple_builtin (decl))
 	  return 0;
 	else if (is_inexpensive_builtin (decl))
 	  return weights->target_builtin_call_cost;
-	else
-	  cost = weights->call_cost;
+	else if (DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL)
+	  {
+	    /* We canonicalize x * x to pow (x, 2.0) with -ffast-math, so
+	       specialize the cheap expansion we do here.
+	       ???  This asks for a more general solution.  */
+	    switch (DECL_FUNCTION_CODE (decl))
+	      {
+		case BUILT_IN_POW:
+		case BUILT_IN_POWF:
+		case BUILT_IN_POWL:
+		  if (TREE_CODE (gimple_call_arg (stmt, 1)) == REAL_CST
+		      && REAL_VALUES_EQUAL
+			   (TREE_REAL_CST (gimple_call_arg (stmt, 1)), dconst2))
+		    return estimate_operator_cost (MULT_EXPR, weights,
+						   gimple_call_arg (stmt, 0),
+						   gimple_call_arg (stmt, 0));
+		  break;
+
+		default:
+		  break;
+	      }
+	  }
 
+	cost = weights->call_cost;
 	if (decl)
 	  funtype = TREE_TYPE (decl);