[Bug tree-optimization/64130] vrp: handle non zero constant divided by range cannot be zero.

[kugan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64130

kugan at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kugan at gcc dot gnu.org

--- Comment #5 from kugan at gcc dot gnu.org ---
I think it should be in from front-end? 

Tried fixing it in VRP like:

--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -9943,12 +9943,43 @@ 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);

       switch (rhs_code)
        {
        case EQ_EXPR:
        case NE_EXPR:
-          /* Transform EQ_EXPR, NE_EXPR into BIT_XOR_EXPR or identity
+
+         /* PR64130.  If there is a statement (integer_cst / var == 0) and
+            integer_cst >= TYPE_MAX (TREE_TYPE (var))
+            then (integer_cst / var) cannot be 0. Hence this condition will
+            be always false.  */
+         if (rhs_code == EQ_EXPR
+             && TREE_CODE (rhs1) == SSA_NAME
+             && integer_zerop (rhs2))
+           {
+             gimple g = SSA_NAME_DEF_STMT (rhs1);
+
+             if (is_gimple_assign (g)
+                 && INTEGRAL_TYPE_P (TREE_TYPE (gimple_assign_rhs1 (g)))
+                 && TREE_CODE (gimple_assign_rhs1 (g)) == INTEGER_CST
+                 && TREE_CODE (gimple_assign_rhs2 (g)) == SSA_NAME
+                 && gimple_assign_rhs_code (g) == TRUNC_DIV_EXPR)
+               {
+                 tree r1 = gimple_assign_rhs1 (g);
+                 tree r2 = gimple_assign_rhs2 (g);
+                 tree max = TYPE_MAX_VALUE (TREE_TYPE (r2));
+                 if (compare_values (r1, max) == -1
+                     || compare_values (r1, max) == 0)
+                   {
+                     gimple_assign_set_rhs_with_ops (gsi, NOP_EXPR, rhs2);
+                     update_stmt (stmt);
+                     return true;
+                   }
+               }
+           }
+
+         /* Transform EQ_EXPR, NE_EXPR into BIT_XOR_EXPR or identity
             if the RHS is zero or one, and the LHS are known to be boolean
             values.  */
          if (INTEGRAL_TYPE_P (TREE_TYPE (rhs1)))


But by the time we are in VRP, variable "a" is already promoted to that fits
the constant.