[PATCH] Improve VRP for sign-changed/widened compares

[Richard Biener]

This improves VRP for cases of

  x = (T) y;
  if (y !=/== CST)
    {
      ... use of X

to insert asserts for X similar to how we handle x = y +- CST.

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

Richard.

2015-06-30  Richard Biener  <rguent...@suse.de>

        * tree-vrp.c (register_edge_assert_for_2): Also register
        asserts for dominating conversion results.

Index: gcc/tree-vrp.c
===================================================================
*** gcc/tree-vrp.c      (revision 225115)
--- gcc/tree-vrp.c      (working copy)
*************** register_edge_assert_for_2 (tree name, e
*** 5359,5365 ****
    /* In the case of post-in/decrement tests like if (i++) ... and uses
       of the in/decremented value on the edge the extra name we want to
       assert for is not on the def chain of the name compared.  Instead
!      it is in the set of use stmts.  */
    if ((comp_code == NE_EXPR
         || comp_code == EQ_EXPR)
        && TREE_CODE (val) == INTEGER_CST)
--- 5359,5367 ----
    /* In the case of post-in/decrement tests like if (i++) ... and uses
       of the in/decremented value on the edge the extra name we want to
       assert for is not on the def chain of the name compared.  Instead
!      it is in the set of use stmts.
!      Similar cases happen for conversions that were simplified through
!      fold_{sign_changed,widened}_comparison.  */
    if ((comp_code == NE_EXPR
         || comp_code == EQ_EXPR)
        && TREE_CODE (val) == INTEGER_CST)
*************** register_edge_assert_for_2 (tree name, e
*** 5368,5396 ****
        gimple use_stmt;
        FOR_EACH_IMM_USE_STMT (use_stmt, ui, name)
        {
-         /* Cut off to use-stmts that are in the predecessor.  */
-         if (gimple_bb (use_stmt) != e->src)
-           continue;
- 
          if (!is_gimple_assign (use_stmt))
            continue;
  
!         enum tree_code code = gimple_assign_rhs_code (use_stmt);
!         if (code != PLUS_EXPR
!             && code != MINUS_EXPR)
            continue;
  
!         tree cst = gimple_assign_rhs2 (use_stmt);
!         if (TREE_CODE (cst) != INTEGER_CST)
            continue;
  
!         tree name2 = gimple_assign_lhs (use_stmt);
!         if (live_on_edge (e, name2))
            {
              cst = int_const_binop (code, val, cst);
-             register_new_assert_for (name2, name2, comp_code, cst,
-                                      NULL, e, bsi);
            }
        }
      }
   
--- 5370,5406 ----
        gimple use_stmt;
        FOR_EACH_IMM_USE_STMT (use_stmt, ui, name)
        {
          if (!is_gimple_assign (use_stmt))
            continue;
  
!         /* Cut off to use-stmts that are dominating the predecessor.  */
!         if (!dominated_by_p (CDI_DOMINATORS, e->src, gimple_bb (use_stmt)))
            continue;
  
!         tree name2 = gimple_assign_lhs (use_stmt);
!         if (TREE_CODE (name2) != SSA_NAME
!             || !live_on_edge (e, name2))
            continue;
  
!         enum tree_code code = gimple_assign_rhs_code (use_stmt);
!         tree cst;
!         if (code == PLUS_EXPR
!             || code == MINUS_EXPR)
            {
+             cst = gimple_assign_rhs2 (use_stmt);
+             if (TREE_CODE (cst) != INTEGER_CST)
+               continue;
              cst = int_const_binop (code, val, cst);
            }
+         else if (CONVERT_EXPR_CODE_P (code))
+           cst = fold_convert (TREE_TYPE (name2), val);
+         else
+           continue;
+ 
+         if (TREE_OVERFLOW_P (cst))
+           cst = drop_tree_overflow (cst);
+         register_new_assert_for (name2, name2, comp_code, cst,
+                                  NULL, e, bsi);
        }
      }