Submitted by Richard Guenther on July 11, 2011, 12:12 p.m.

Message ID | alpine.LNX.2.00.1107111412220.810@zhemvz.fhfr.qr |
---|---|

State | New |

Headers | show |

Hi, On Mon, 11 Jul 2011, Richard Guenther wrote: > The following actually works. > > Bootstrapped and tested on x86_64-unknown-linux-gnu. > > Can you double-check it? Seems sensible. Given this: short s; int i; for (s = 0; s <= 127; s++) i += (signed char)(unsigned char)s; return i; (or similar), does it remove the conversions to signed and unsigned char now? And does it _not_ remove them if the upper bound is 128, or the lower bound is -1 ? Similar (now with extensions): signed char c; unsigned u; for (c = 1; c < 127; c++) u += (unsigned)(int)c; The conversion to int is not necessary; but it is when the lower bound is -1. Ciao, Michael.

On Mon, Jul 11, 2011 at 5:12 AM, Richard Guenther <rguenther@suse.de> wrote: > On Fri, 8 Jul 2011, Richard Guenther wrote: > >> On Fri, 8 Jul 2011, Michael Matz wrote: >> >> > Hi, >> > >> > On Fri, 8 Jul 2011, Richard Guenther wrote: >> > >> > > It should be indeed safe with the current handling of conversions, but >> > > better be safe. So, like the following? >> > >> > No. The point is that you can't compare the bounds that VRP computes with >> > each other when the outcome affects correctness. Think about a very >> > trivial and stupid VRP, that assigns the range [WIDEST_INT_MIN .. >> > WIDEST_UINT_MAX] to each and every SSA name without looking at types and >> > operations at all (assuming that this reflects the largest int type on the >> > target). It's useless but correct. Of course we wouldn't implement such >> > useless range discovery, but similar situations can arise when some VRP >> > algorithms give up for certain reasons, or computation of tight bounds >> > merely isn't implemented for some operations. >> > >> > Your routines need to work also in the presence of such imprecise ranges. >> > >> > Hence, the check that the intermediate conversion is useless needs to take >> > into account the input value range (that's conservatively correct), and >> > the precision and signedness of the target type (if it can represent all >> > value of the input range the conversion was useless). It must not look at >> > the suspected value range of the destination, precisely because it is >> > conservative only. >> >> Ok, indeed conservative is different for what VRP does and for what >> a transformation must assess. So the following patch makes >> a conservative attempt at checking the transformation (which of >> course non-surprisingly matches what the VRP part does). >> >> So, more like the following? > > The following actually works. > > Bootstrapped and tested on x86_64-unknown-linux-gnu. > > Can you double-check it? > > Thanks, > Richard. > > 2011-07-11 Richard Guenther <rguenther@suse.de> > > * tree-vrp.c (simplify_conversion_using_ranges): Manually > translate the source value-range through the conversion chain. > This may have caused: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50066

Index: gcc/tree-vrp.c =================================================================== --- gcc/tree-vrp.c (revision 176030) +++ gcc/tree-vrp.c (working copy) @@ -7347,30 +7347,55 @@ simplify_switch_using_ranges (gimple stm static bool simplify_conversion_using_ranges (gimple stmt) { - tree rhs1 = gimple_assign_rhs1 (stmt); - gimple def_stmt = SSA_NAME_DEF_STMT (rhs1); - value_range_t *final, *inner; + tree innerop, middleop, finaltype; + gimple def_stmt; + value_range_t *innervr; + double_int innermin, innermax, middlemin, middlemax; - /* 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; + finaltype = TREE_TYPE (gimple_assign_lhs (stmt)); + middleop = gimple_assign_rhs1 (stmt); + def_stmt = SSA_NAME_DEF_STMT (middleop); 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) + innerop = gimple_assign_rhs1 (def_stmt); + if (TREE_CODE (innerop) != SSA_NAME) return false; - inner = get_value_range (rhs1); - if (inner->type != VR_RANGE) + + /* Get the value-range of the inner operand. */ + innervr = get_value_range (innerop); + if (innervr->type != VR_RANGE + || TREE_CODE (innervr->min) != INTEGER_CST + || TREE_CODE (innervr->max) != INTEGER_CST) return false; - /* If the value-range is preserved by the conversion sequence strip - the intermediate conversion. */ - if (!tree_int_cst_equal (final->min, inner->min) - || !tree_int_cst_equal (final->max, inner->max)) + + /* Simulate the conversion chain to check if the result is equal if + the middle conversion is removed. */ + innermin = tree_to_double_int (innervr->min); + innermax = tree_to_double_int (innervr->max); + middlemin = double_int_ext (innermin, TYPE_PRECISION (TREE_TYPE (middleop)), + TYPE_UNSIGNED (TREE_TYPE (middleop))); + middlemax = double_int_ext (innermax, TYPE_PRECISION (TREE_TYPE (middleop)), + TYPE_UNSIGNED (TREE_TYPE (middleop))); + /* If the middle values do not represent a proper range fail. */ + if (double_int_cmp (middlemin, middlemax, + TYPE_UNSIGNED (TREE_TYPE (middleop))) > 0) return false; - gimple_assign_set_rhs1 (stmt, rhs1); + if (!double_int_equal_p (double_int_ext (middlemin, + TYPE_PRECISION (finaltype), + TYPE_UNSIGNED (finaltype)), + double_int_ext (innermin, + TYPE_PRECISION (finaltype), + TYPE_UNSIGNED (finaltype))) + || !double_int_equal_p (double_int_ext (middlemax, + TYPE_PRECISION (finaltype), + TYPE_UNSIGNED (finaltype)), + double_int_ext (innermax, + TYPE_PRECISION (finaltype), + TYPE_UNSIGNED (finaltype)))) + return false; + + gimple_assign_set_rhs1 (stmt, innerop); update_stmt (stmt); return true; }