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[RFA][PATCH] Improve VRP of COND_EXPR_CONDs



Given something like this:

 <bb 6>:
  _23 = changed_17 ^ 1;
  _12 = (_Bool) _23;
  if (_12 != 0)
    goto <bb 10>;
  else
    goto <bb 7>;

Assume _23 and changed_17 have integer types wider than a boolean, but VRP has determined they have a range [0..1].

We should be turning that into:

 <bb 6>:
  _23 = changed_17 ^ 1;
  _12 = (_Bool) _23;
  if (_23 != 0)
    goto <bb 10>;
  else
    goto <bb 7>;

Note the change in the conditional.  This also makes the statement
_12 = (_Bool) _23 dead which should be eliminated by DCE.

This kind of thing happens regularly in GCC itself and is fixed by the attached patch.

Bootstrapped and regression tested on x86_64-unknown-linux-gnu.

OK for the trunk?

commit fd82eea6f208bb12646e0e0e307fb86f043c1649
Author: Jeff Law <law@redhat.com>
Date:   Sat Apr 6 06:46:58 2013 -0600

           * tree-vrp.c (simplify_cond_using_ranges): Simplify test of boolean
           when the boolean was created by converting a wider object which
           had a boolean range.
    
            * gcc.dg/tree-ssa/vrp87.c: New test

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 44797cc..d34ecde 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,9 @@
 2013-04-06  Jeff Law  <law@redhat.com>
 
+	* tree-vrp.c (simplify_cond_using_ranges): Simplify test of boolean
+	when the boolean was created by converting a wider object which
+	had a boolean range.
+
 	* gimple.c (canonicalize_cond_expr_cond): Rewrite x ^ y into
 	x != y.
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 601ca66..6ed8af2 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,7 @@
 2013-04-06  Jeff Law  <law@redhat.com>
 
+	* gcc.dg/tree-ssa/vrp87.c: New test
+
 	* gcc.dg/tree-ssa/forwprop-25.c: New test
 
 2013-04-03  Jeff Law  <law@redhat.com>
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp87.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp87.c
new file mode 100644
index 0000000..7feff81
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp87.c
@@ -0,0 +1,81 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-vrp2-details -fdump-tree-cddce2-details" } */
+
+struct bitmap_head_def;
+typedef struct bitmap_head_def *bitmap;
+typedef const struct bitmap_head_def *const_bitmap;
+
+
+typedef unsigned long BITMAP_WORD;
+typedef struct bitmap_element_def
+{
+  struct bitmap_element_def *next;
+  unsigned int indx;
+  BITMAP_WORD bits[((128 + (8 * 8 * 1u) - 1) / (8 * 8 * 1u))];
+} bitmap_element;
+
+
+
+
+
+
+typedef struct bitmap_head_def
+{
+  bitmap_element *first;
+
+} bitmap_head;
+
+
+
+static __inline__ unsigned char
+bitmap_elt_ior (bitmap dst, bitmap_element * dst_elt,
+		bitmap_element * dst_prev, const bitmap_element * a_elt,
+		const bitmap_element * b_elt, unsigned char changed)
+{
+
+  if (a_elt)
+    {
+
+      if (!changed && dst_elt)
+	{
+	  changed = 1;
+	}
+    }
+  else
+    {
+      changed = 1;
+    }
+  return changed;
+}
+
+unsigned char
+bitmap_ior_into (bitmap a, const_bitmap b)
+{
+  bitmap_element *a_elt = a->first;
+  const bitmap_element *b_elt = b->first;
+  bitmap_element *a_prev = ((void *) 0);
+  unsigned char changed = 0;
+
+  while (b_elt)
+    {
+
+      if (!a_elt || a_elt->indx == b_elt->indx)
+	changed = bitmap_elt_ior (a, a_elt, a_prev, a_elt, b_elt, changed);
+      else if (a_elt->indx > b_elt->indx)
+	changed = 1;
+      b_elt = b_elt->next;
+
+
+    }
+
+  return changed;
+}
+
+/* Verify that VRP simplified an "if" statement.  */
+/* { dg-final { scan-tree-dump "Folded into: if.*" "vrp2"} } */
+/* Verify that DCE after VRP2 eliminates a dead conversion
+   to a (Bool).  */
+/* { dg-final { scan-tree-dump "Deleting.*_Bool.*;" "cddce2"} } */
+/* { dg-final { cleanup-tree-dump "vrp2" } } */
+/* { dg-final { cleanup-tree-dump "cddce2" } } */
+
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 250a506..d76cead 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -8584,6 +8584,43 @@ simplify_cond_using_ranges (gimple stmt)
 	}
     }
 
+  /* If we have a comparison of a SSA_NAME boolean against
+     a constant (which obviously must be [0..1]).  See if the
+     SSA_NAME was set by a type conversion where the source
+     of the conversion is another SSA_NAME with a range [0..1].
+
+     If so, we can replace the SSA_NAME in the comparison with
+     the RHS of the conversion.  This will often make the type
+     conversion dead code which DCE will clean up.  */
+  if (TREE_CODE (op0) == SSA_NAME
+      && TREE_CODE (TREE_TYPE (op0)) == BOOLEAN_TYPE
+      && is_gimple_min_invariant (op1))
+    {
+      gimple def_stmt = SSA_NAME_DEF_STMT (op0);
+      tree innerop;
+
+      if (!is_gimple_assign (def_stmt)
+	  || !CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt)))
+	return false;
+
+      innerop = gimple_assign_rhs1 (def_stmt);
+
+      if (!SSA_NAME_OCCURS_IN_ABNORMAL_PHI (innerop))
+	{
+	  value_range_t *vr = get_value_range (innerop);
+
+          if (vr->type == VR_RANGE
+	      && operand_equal_p (vr->min, integer_zero_node, 0)
+	      && operand_equal_p (vr->max, integer_one_node, 0))
+	    {
+	      tree newconst = fold_convert (TREE_TYPE (innerop), op1);
+	      gimple_cond_set_lhs (stmt, innerop);
+	      gimple_cond_set_rhs (stmt, newconst);
+	      return true;
+	    }
+	}
+    }
+
   return false;
 }
 

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