[patch] tree-vrp.c: Remove has_assert_expr.

[Kazu Hirata <kazu at cs dot umass dot edu>]

Hi,

Attached is a patch to remove has_assert_expr as it is currently a
no-op.

AFAICT, has_assert_expr was designed to avoid insertions of redundant
ASSERT_EXPRs.  For example, given

  p->a = 3;
  p->b = 5;

we do not want to insert two ASSERT_EXPRs like so

  p->a = 3;
  p = ASSERT_EXPR <p, p != 0B>;
  p->b = 5;
  p = ASSERT_EXPR <p, p != 0B>;

because the second is totally redundant given the first one.  However,
it's not functioning at all.  The reason is that it always returns
false immediately.

  if (TREE_CODE (def_stmt) != MODIFY_EXPR
      || TREE_CODE (TREE_OPERAND (def_stmt, 1)) != ASSERT_EXPR)
    return false;

While inserting ASSERT_EXPRs, there is no SSA_NAME that has at least
one use and is defined by an ASERT_EXPR.  This is because ASSERT_EXPRs
are born in VRP.  They aren't present in prior passes.

Tested on i686-pc-linux-gnu.  OK to apply?

p.s.
I am playing with a quick-n-dirty pruning now.  Specifically, for each
SSA_NAME, I am keeping track of a basic block where a "nonnull"
ASSERT_EXPR is last inserted.  This cuts down the number of
ASSERT_EXPRs significantly, about 50%.  I'll post a separate message
about this.

Kazu Hirata

2005-05-04  Kazu Hirata  <kazu@cs.umass.edu>

	PR tree-optimization/pr21348
	* tree-vrp.c (has_assert_expr): Remove.
	(maybe_add_assert_expr): Don't call has_assert_expr.

Index: tree-vrp.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-vrp.c,v
retrieving revision 2.16
diff -u -d -p -r2.16 tree-vrp.c
--- tree-vrp.c	2 May 2005 22:54:37 -0000	2.16
+++ tree-vrp.c	3 May 2005 02:23:50 -0000
@@ -1431,61 +1431,6 @@ infer_value_range (tree stmt, tree op)
 }
 
 
-/* Return true if OP is the result of an ASSERT_EXPR that tests the
-   same condition as COND.  */
-
-static bool
-has_assert_expr (tree op, tree cond)
-{
-  tree def_stmt = SSA_NAME_DEF_STMT (op);
-  tree assert_expr, other_cond, other_op;
-
-  /* If OP was not generated by an ASSERT_EXPR, return false.  */
-  if (TREE_CODE (def_stmt) != MODIFY_EXPR
-      || TREE_CODE (TREE_OPERAND (def_stmt, 1)) != ASSERT_EXPR)
-    return false;
-
-  assert_expr = TREE_OPERAND (def_stmt, 1);
-  other_cond = ASSERT_EXPR_COND (assert_expr);
-  other_op = ASSERT_EXPR_VAR (assert_expr);
-
-  if (TREE_CODE (cond) == TREE_CODE (other_cond))
-    {
-      tree t1, t2;
-
-      /* If COND is not a comparison predicate, something is wrong.  */
-      gcc_assert (COMPARISON_CLASS_P (cond));
-
-      /* Note that we only need to compare against one of the operands
-	 of OTHER_COND.  
-	 
-	 Suppose that we are about to insert the assertion ASSERT_EXPR
-	 <x_4, x_4 != 0> and the defining statement for x_4 is x_4 =
-	 ASSERT_EXPR <x_3, x_3 != 0>.
-
-	 In this case, we don't really want to insert a new
-	 ASSERT_EXPR for x_4 because that would be redundant.  We
-	 already know that x_4 is not 0.  So, when comparing the
-	 conditionals 'x_3 != 0' and 'x_4 != 0', we don't want to
-	 compare x_3 and x_4, we just want to compare the predicate's
-	 code (!=) and the other operand (0).  */
-      if (TREE_OPERAND (cond, 0) == op)
-	t1 = TREE_OPERAND (cond, 1);
-      else
-	t1 = TREE_OPERAND (cond, 0);
-
-      if (TREE_OPERAND (other_cond, 0) == other_op)
-	t2 = TREE_OPERAND (other_cond, 1);
-      else
-	t2 = TREE_OPERAND (other_cond, 0);
-
-      return (t1 == t2 || operand_equal_p (t1, t2, 0));
-    }
-
-  return false;
-}
-
-
 /* Traverse all the statements in block BB looking for used variables.
    Variables used in BB are added to bitmap FOUND.  The algorithm
    works in three main parts:
@@ -1584,9 +1529,6 @@ maybe_add_assert_expr (basic_block bb)
 	     (unless OP already has an ASSERT_EXPR).  */
 	  gcc_assert (!is_ctrl_stmt (stmt));
 
-	  if (has_assert_expr (op, cond))
-	    continue;
-
 	  if (!stmt_ends_bb_p (stmt))
 	    {
 	      /* If STMT does not end the block, we can insert the new