phiopt: Improve minmax optimization [PR95699]

As discussed in the PR, the
x < 0x80000000U to (int) x >= 0
optimization stands in the way of minmax_replacement optimization,
so for comparisons with most of the constants it works well, but when the
above mentioned optimization triggers, it is unable to do it.
The match.pd (cond (cmp (convert? x) c1) (op x c2) c3) -> (op (minmax x c1) c2)
optimization is able to look through that and this patch
teaches minmax_replacement about it too.

2020-06-18  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/95699
	* tree-ssa-phiopt.c (minmax_replacement): Treat (signed int)x < 0
	as x > INT_MAX and (signed int)x >= 0 as x <= INT_MAX.  Move variable
	declarations to the statements that set them where possible.

	* gcc.dg/tree-ssa/pr95699.c: New test.

1 files changed, 53 insertions, 10 deletions

diff --git a/gcc/tree-ssa-phiopt.c b/gcc/tree-ssa-phiopt.c
index 5f283890..b97f863 100644
--- a/gcc/tree-ssa-phiopt.c
+++ b/gcc/tree-ssa-phiopt.c
@@ -1363,22 +1363,21 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb,
 		    edge e0, edge e1, gimple *phi,
 		    tree arg0, tree arg1)
 {
-  tree result, type, rhs;
-  gcond *cond;
+  tree result;
   edge true_edge, false_edge;
-  enum tree_code cmp, minmax, ass_code;
-  tree smaller, alt_smaller, larger, alt_larger, arg_true, arg_false;
+  enum tree_code minmax, ass_code;
+  tree smaller, larger, arg_true, arg_false;
   gimple_stmt_iterator gsi, gsi_from;
 
-  type = TREE_TYPE (PHI_RESULT (phi));
+  tree type = TREE_TYPE (PHI_RESULT (phi));
 
   /* The optimization may be unsafe due to NaNs.  */
   if (HONOR_NANS (type) || HONOR_SIGNED_ZEROS (type))
     return false;
 
-  cond = as_a <gcond *> (last_stmt (cond_bb));
-  cmp = gimple_cond_code (cond);
-  rhs = gimple_cond_rhs (cond);
+  gcond *cond = as_a <gcond *> (last_stmt (cond_bb));
+  enum tree_code cmp = gimple_cond_code (cond);
+  tree rhs = gimple_cond_rhs (cond);
 
   /* Turn EQ/NE of extreme values to order comparisons.  */
   if ((cmp == NE_EXPR || cmp == EQ_EXPR)
@@ -1401,8 +1400,8 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb,
 
   /* This transformation is only valid for order comparisons.  Record which
      operand is smaller/larger if the result of the comparison is true.  */
-  alt_smaller = NULL_TREE;
-  alt_larger = NULL_TREE;
+  tree alt_smaller = NULL_TREE;
+  tree alt_larger = NULL_TREE;
   if (cmp == LT_EXPR || cmp == LE_EXPR)
     {
       smaller = gimple_cond_lhs (cond);
@@ -1463,6 +1462,50 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb,
   else
     return false;
 
+  /* Handle the special case of (signed_type)x < 0 being equivalent
+     to x > MAX_VAL(signed_type) and (signed_type)x >= 0 equivalent
+     to x <= MAX_VAL(signed_type).  */
+  if ((cmp == GE_EXPR || cmp == LT_EXPR)
+      && INTEGRAL_TYPE_P (type)
+      && TYPE_UNSIGNED (type)
+      && integer_zerop (rhs))
+    {
+      tree op = gimple_cond_lhs (cond);
+      if (TREE_CODE (op) == SSA_NAME
+	  && INTEGRAL_TYPE_P (TREE_TYPE (op))
+	  && !TYPE_UNSIGNED (TREE_TYPE (op)))
+	{
+	  gimple *def_stmt = SSA_NAME_DEF_STMT (op);
+	  if (gimple_assign_cast_p (def_stmt))
+	    {
+	      tree op1 = gimple_assign_rhs1 (def_stmt);
+	      if (INTEGRAL_TYPE_P (TREE_TYPE (op1))
+		  && TYPE_UNSIGNED (TREE_TYPE (op1))
+		  && (TYPE_PRECISION (TREE_TYPE (op))
+		      == TYPE_PRECISION (TREE_TYPE (op1)))
+		  && useless_type_conversion_p (type, TREE_TYPE (op1)))
+		{
+		  wide_int w1 = wi::max_value (TREE_TYPE (op));
+		  wide_int w2 = wi::add (w1, 1);
+		  if (cmp == LT_EXPR)
+		    {
+		      larger = op1;
+		      smaller = wide_int_to_tree (TREE_TYPE (op1), w1);
+		      alt_smaller = wide_int_to_tree (TREE_TYPE (op1), w2);
+		      alt_larger = NULL_TREE;
+		    }
+		  else
+		    {
+		      smaller = op1;
+		      larger = wide_int_to_tree (TREE_TYPE (op1), w1);
+		      alt_larger = wide_int_to_tree (TREE_TYPE (op1), w2);
+		      alt_smaller = NULL_TREE;
+		    }
+		}
+	    }
+	}
+    }
+
   /* We need to know which is the true edge and which is the false
       edge so that we know if have abs or negative abs.  */
   extract_true_false_edges_from_block (cond_bb, &true_edge, &false_edge);