[PATCH] Remove some useless work in PRE

[PATCH] Remove some useless work in PRE

[Richard Biener]

VN already sees if an expresion is fully constant so there's no reason
to duplicate that work during PHI translation.  I've verified with
an assert the paths are indeed unreachable.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.

Richard.

2017-11-17  Richard Biener  <rguenther@suse.de>

	* tree-ssa-pre.c (phi_translate_1): Remove redundant constant
	folding of references.

Index: gcc/tree-ssa-pre.c
===================================================================
--- gcc/tree-ssa-pre.c	(revision 254797)
+++ gcc/tree-ssa-pre.c	(working copy)
@@ -1566,7 +1566,6 @@ phi_translate_1 (pre_expr expr, bitmap_s
 	if (changed || newvuse != vuse)
 	  {
 	    unsigned int new_val_id;
-	    pre_expr constant;
 
 	    tree result = vn_reference_lookup_pieces (newvuse, ref->set,
 						      ref->type,
@@ -1611,15 +1610,7 @@ phi_translate_1 (pre_expr expr, bitmap_s
 	    expr->id = 0;
 
 	    if (newref)
-	      {
-		PRE_EXPR_REFERENCE (expr) = newref;
-		constant = fully_constant_expression (expr);
-		if (constant != expr)
-		  return constant;
-
-		new_val_id = newref->value_id;
-		get_or_alloc_expression_id (expr);
-	      }
+	      new_val_id = newref->value_id;
 	    else
 	      {
 		if (changed || !same_valid)
@@ -1637,12 +1628,9 @@ phi_translate_1 (pre_expr expr, bitmap_s
 						     newoperands,
 						     result, new_val_id);
 		newoperands = vNULL;
-		PRE_EXPR_REFERENCE (expr) = newref;
-		constant = fully_constant_expression (expr);
-		if (constant != expr)
-		  return constant;
-		get_or_alloc_expression_id (expr);
 	      }
+	    PRE_EXPR_REFERENCE (expr) = newref;
+	    get_or_alloc_expression_id (expr);
 	    add_to_value (new_val_id, expr);
 	  }
 	newoperands.release ();