[RFC][PR61839]Convert CST BINOP COND_EXPR to COND_EXPR ? (CST BINOP 1) : (CST BINOP 0)

[kugan]

As explained in PR61839,

Following difference results in extra instructions:
-  c = b != 0 ? 486097858 : 972195717;
+  c = a + 972195718 >> (b != 0);
As suggested in PR, attached patch converts CST BINOP COND_EXPR to 
COND_EXPR ? (CST BINOP 1) : (CST BINOP 0).

Bootstrapped and regression tested for x86-64-linux-gnu with no new 
regression. Is this OK for statege-1.

Thanks,
Kugan

gcc/ChangeLog:

2016-04-17  Kugan Vivekanandarajah  <kug...@linaro.org>

        * tree-vrp.c (simplify_stmt_using_ranges): Convert CST BINOP COND_EXPR 
to
        COND_EXPR ? (CST BINOP 1) : (CST BINOP 0) when possible.
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index bbdf9ce..caf7a2a 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -9902,6 +9902,49 @@ simplify_stmt_using_ranges (gimple_stmt_iterator *gsi)
     {
       enum tree_code rhs_code = gimple_assign_rhs_code (stmt);
       tree rhs1 = gimple_assign_rhs1 (stmt);
+      tree rhs2 = gimple_assign_rhs2 (stmt);
+      tree var;
+
+      /* Convert:
+        COND_RES = X COMPARE Y
+        TMP = (CAST) COND_RES
+        LHS = CST BINOP TMP
+
+        To:
+        LHS = COND_RES ? (CST BINOP 1) : (CST BINOP 0) */
+
+      if (TREE_CODE_CLASS (rhs_code) == tcc_binary
+         && TREE_CODE (rhs1) == INTEGER_CST
+         && TREE_CODE (rhs2) == SSA_NAME
+         && is_gimple_assign (SSA_NAME_DEF_STMT (rhs2))
+         && gimple_assign_rhs_code (SSA_NAME_DEF_STMT (rhs2)) == NOP_EXPR
+         && (var = gimple_assign_rhs1 (SSA_NAME_DEF_STMT (rhs2)))
+         && TREE_CODE (var) == SSA_NAME
+         && is_gimple_assign (SSA_NAME_DEF_STMT (var))
+         && TREE_CODE_CLASS (gimple_assign_rhs_code (SSA_NAME_DEF_STMT (var)))
+         == tcc_comparison)
+
+       {
+         value_range *vr = get_value_range (var);
+         if (range_int_cst_p (vr)
+             && integer_zerop (vr->min)
+             && integer_onep (vr->max))
+           {
+
+             tree new_rhs1 =  int_const_binop (rhs_code, rhs1, vr->max);
+             tree new_rhs2 =  int_const_binop (rhs_code, rhs1, vr->min);
+
+             if (new_rhs1 && new_rhs2)
+               {
+                 gimple_assign_set_rhs_with_ops (gsi,
+                                                 COND_EXPR, var,
+                                                 new_rhs1,
+                                                 new_rhs2);
+                 update_stmt (gsi_stmt (*gsi));
+                 return true;
+               }
+           }
+       }
 
       switch (rhs_code)
        {