[PATCH] Fix PR71059

[PATCH] Fix PR71059

[Richard Biener]

The following works around the issue that PRE inserts expressions into
the VN hashes without having a representative for them.  First the
patch avoids inserting fully constant expressions and second it deals
with the above by assigning a representative once VN insertion needs one.

The way PRE uses the VN hashes here probably needs some (big) overhaul
but the following should get us past the failure point in a reasonable
way as well.

Bootstrap and regtest running on x86_64-unknown-linux-gnu.

Richard.

2016-05-11  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/71059
	* tree-ssa-pre.c (phi_translate_1): Fully fold translated
	nary before looking up or entering the expression into the VN
	hashes.
	* tree-ssa-sccvn.c (vn_nary_build_or_lookup): Fix comment typo.
	Make sure to re-use NARYs without result as inserted by
	phi-translation.

	* gcc.dg/torture/pr71059.c: New testcase.

Index: gcc/tree-ssa-pre.c
===================================================================
*** gcc/tree-ssa-pre.c	(revision 236069)
--- gcc/tree-ssa-pre.c	(working copy)
*************** phi_translate_1 (pre_expr expr, bitmap_s
*** 1464,1469 ****
--- 1464,1475 ----
  	    pre_expr constant;
  	    unsigned int new_val_id;
  
+ 	    PRE_EXPR_NARY (expr) = newnary;
+ 	    constant = fully_constant_expression (expr);
+ 	    PRE_EXPR_NARY (expr) = nary;
+ 	    if (constant != expr)
+ 	      return constant;
+ 
  	    tree result = vn_nary_op_lookup_pieces (newnary->length,
  						    newnary->opcode,
  						    newnary->type,
*************** phi_translate_1 (pre_expr expr, bitmap_s
*** 1478,1487 ****
  	    if (nary)
  	      {
  		PRE_EXPR_NARY (expr) = nary;
- 		constant = fully_constant_expression (expr);
- 		if (constant != expr)
- 		  return constant;
- 
  		new_val_id = nary->value_id;
  		get_or_alloc_expression_id (expr);
  	      }
--- 1484,1489 ----
*************** phi_translate_1 (pre_expr expr, bitmap_s
*** 1495,1503 ****
  						 &newnary->op[0],
  						 result, new_val_id);
  		PRE_EXPR_NARY (expr) = nary;
- 		constant = fully_constant_expression (expr);
- 		if (constant != expr)
- 		  return constant;
  		get_or_alloc_expression_id (expr);
  	      }
  	    add_to_value (new_val_id, expr);
--- 1497,1502 ----
Index: gcc/testsuite/gcc.dg/torture/pr71059.c
===================================================================
*** gcc/testsuite/gcc.dg/torture/pr71059.c	(revision 0)
--- gcc/testsuite/gcc.dg/torture/pr71059.c	(working copy)
***************
*** 0 ****
--- 1,15 ----
+ /* { dg-do compile } */
+ 
+ short a, c;
+ union {
+     unsigned f0;
+     unsigned short f1;
+ } b;
+ volatile int d;
+ short fn1(short p1) { return p1 + a; }
+ void fn2()
+ {
+   b.f0 = 0;
+   for (;; b.f0 = fn1(b.f0))
+     (c && b.f1) || d;
+ }
Index: gcc/tree-ssa-sccvn.c
===================================================================
*** gcc/tree-ssa-sccvn.c	(revision 236159)
--- gcc/tree-ssa-sccvn.c	(working copy)
*************** vn_nary_build_or_lookup (code_helper rco
*** 1632,1638 ****
  {
    tree result = NULL_TREE;
    /* We will be creating a value number for
!        ROCDE (OPS...).
       So first simplify and lookup this expression to see if it
       is already available.  */
    mprts_hook = vn_lookup_simplify_result;
--- 1632,1638 ----
  {
    tree result = NULL_TREE;
    /* We will be creating a value number for
!        RCODE (OPS...).
       So first simplify and lookup this expression to see if it
       is already available.  */
    mprts_hook = vn_lookup_simplify_result;
*************** vn_nary_build_or_lookup (code_helper rco
*** 1682,1687 ****
--- 1682,1697 ----
        gimple_seq_add_stmt_without_update (&VN_INFO (result)->expr,
  					  new_stmt);
        VN_INFO (result)->needs_insertion = true;
+       /* ???  PRE phi-translation inserts NARYs without corresponding
+          SSA name result.  Re-use those but set their result according
+ 	 to the stmt we just built.  */
+       vn_nary_op_t nary = NULL;
+       vn_nary_op_lookup_stmt (new_stmt, &nary);
+       if (nary)
+ 	{
+ 	  gcc_assert (nary->result == NULL_TREE);
+ 	  nary->result = gimple_assign_lhs (new_stmt);
+ 	}
        /* As all "inserted" statements are singleton SCCs, insert
  	 to the valid table.  This is strictly needed to
  	 avoid re-generating new value SSA_NAMEs for the same
*************** vn_nary_build_or_lookup (code_helper rco
*** 1689,1695 ****
  	 optimistic table gets cleared after each iteration).
  	 We do not need to insert into the optimistic table, as
  	 lookups there will fall back to the valid table.  */
!       if (current_info == optimistic_info)
  	{
  	  current_info = valid_info;
  	  vn_nary_op_insert_stmt (new_stmt, result);
--- 1699,1705 ----
  	 optimistic table gets cleared after each iteration).
  	 We do not need to insert into the optimistic table, as
  	 lookups there will fall back to the valid table.  */
!       else if (current_info == optimistic_info)
  	{
  	  current_info = valid_info;
  	  vn_nary_op_insert_stmt (new_stmt, result);