[Bug tree-optimization/61839] More optimize opportunity for VRP

["kugan at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61839

kugan at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kugan at gcc dot gnu.org
      Known to fail|4.10.0                      |5.0

--- Comment #2 from kugan at gcc dot gnu.org ---

> -  c = b != 0 ? 486097858 : 972195717;
> +  c = a + 972195718 >> (b != 0);

...

> until the very end, not transforming c_6.  Note that VRP could do the
> missing transform as it knows that _5 is [0, 1] (it has to jump through
> the shift - the value-range for the shift itself is too broad).
> 
> If written this kind of transform should be applied more generally, not
> just for shifts.  It basically wants to ask whether a conditional test
> can be carried out against another SSA name (and another constant) if
> an intermediate compute can be omitted in that case.

Do you mean something like,

diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index bbdf9ce..dfce619 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -9902,6 +9902,47 @@ 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)
+
+       {
+         gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
+         value_range *vr = get_value_range (var);
+         if (range_int_cst_p (vr)
+             && integer_zerop (vr->min)
+             && integer_onep (vr->max))
+           {
+
+             tree lhs = gimple_assign_lhs (stmt);
+             tree new_rhs1 =  int_const_binop (rhs_code, rhs1, vr->min);
+             tree new_rhs2 =  int_const_binop (rhs_code, rhs1, vr->max);
+
+             gimple *s = gimple_build_assign (lhs, COND_EXPR, var,
+                                              new_rhs1,
+                                              new_rhs2 PASS_MEM_STAT);
+             gsi_replace (&gsi, s, false);
+             return true;
+           }
+       }

       switch (rhs_code)
        {