Hi, On Thu, 7 Jul 2011, Richard Guenther wrote:
> + tree rhs1 = gimple_assign_rhs1 (stmt); > + gimple def_stmt = SSA_NAME_DEF_STMT (rhs1); > + value_range_t *final, *inner; > + > + /* Obtain final and inner value-ranges for a conversion > + sequence (final-type)(intermediate-type)inner-type. */ > + final = get_value_range (gimple_assign_lhs (stmt)); > + if (final->type != VR_RANGE) > + return false; > + if (!is_gimple_assign (def_stmt) > + || !CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt))) > + return false; > + rhs1 = gimple_assign_rhs1 (def_stmt); > + if (TREE_CODE (rhs1) != SSA_NAME) > + return false; > + inner = get_value_range (rhs1); > + if (inner->type != VR_RANGE) > + return false; > + if (!tree_int_cst_equal (final->min, inner->min) > + || !tree_int_cst_equal (final->max, inner->max)) > + return false; I think that's a bit too conservative. Granted in current VRP it might work, but think about an intermediate truncation plus widening: short s; short d = (short)(signed char)s; It wouldn't be wrong for VRP to assign d the range [-16384,16383], suboptimal but correct. That would trigger your function in removing the truncation, and _that_ would be incorrect. The bounds of VRP aren't reliably tight. You probably want to recheck if the intermediate conversion isn't truncating the known input range of rhs1. Ciao, Michael.
