From 5e6597064b0c7eb93b8f720afc4aa970eefb0628 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Fri, 8 Apr 2022 09:14:44 +0200 Subject: [PATCH] fold-const: Fix up make_range_step [PR105189] The following testcase is miscompiled, because fold_truth_andor incorrectly folds (unsigned) foo () >= 0U && 1 into foo () >= 0 For the unsigned comparison (which is useless in this case, as >= 0U is always true, but hasn't been folded yet), previous make_range_step derives exp (unsigned) foo () and +[0U, -] range for it. Next we process the NOP_EXPR. We have special code for unsigned to signed casts, already earlier punt if low or high aren't representable in arg0_type or if it is a narrowing conversion. For the signed to unsigned casts, I think if high is specified we are still fine, as we punt for non-representable values in arg0_type, n_high is then still representable and so was smaller or equal to signed maximum and either low is not present (equivalent to 0U), or low must be smaller or equal to high and so for unsigned exp +[low, high] the signed exp +[n_low, n_high] will be correct. Similarly, if both low and high aren't specified (always true or always false), it is ok too. But if we have for unsigned exp +[low, -] or -[low, -], using +[n_low, -] or -[n_high, -] is incorrect. Because low is smaller or equal to signed maximum and high is unspecified (i.e. unsigned maximum), when signed that range is a union of +[n_low, -] and +[-, -1] which is equivalent to -[0, n_low-1], unless low is 0, in that case we can treat it as [-, -]. 2022-04-08 Jakub Jelinek PR tree-optimization/105189 * fold-const.cc (make_range_step): Fix up handling of (unsigned) x +[low, -] ranges for signed x if low fits into typeof (x). * g++.dg/torture/pr105189.C: New test. --- gcc/fold-const.cc | 28 ++++++++++++++++++++++++- gcc/testsuite/g++.dg/torture/pr105189.C | 19 +++++++++++++++++ 2 files changed, 46 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/torture/pr105189.C diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc index fb08fa1dbc60..7226bc5af01a 100644 --- a/gcc/fold-const.cc +++ b/gcc/fold-const.cc @@ -5212,7 +5212,7 @@ make_range_step (location_t loc, enum tree_code code, tree arg0, tree arg1, n_high = fold_convert_loc (loc, arg0_type, n_high); /* If we're converting arg0 from an unsigned type, to exp, - a signed type, we will be doing the comparison as unsigned. + a signed type, we will be doing the comparison as unsigned. The tests above have already verified that LOW and HIGH are both positive. @@ -5274,6 +5274,32 @@ make_range_step (location_t loc, enum tree_code code, tree arg0, tree arg1, } } + /* Otherwise, if we are converting arg0 from signed type, to exp, + an unsigned type, we will do the comparison as signed. If + high is non-NULL, we punt above if it doesn't fit in the signed + type, so if we get through here, +[-, high] or +[low, high] are + equivalent to +[-, n_high] or +[n_low, n_high]. Similarly, + +[-, -] or -[-, -] are equivalent too. But if low is specified and + high is not, the +[low, -] range is equivalent to union of + +[n_low, -] and +[-, -1] ranges, so +[low, -] is equivalent to + -[0, n_low-1] and similarly -[low, -] to +[0, n_low-1], except for + low being 0, which should be treated as [-, -]. */ + else if (TYPE_UNSIGNED (exp_type) + && !TYPE_UNSIGNED (arg0_type) + && low + && !high) + { + if (integer_zerop (low)) + n_low = NULL_TREE; + else + { + n_high = fold_build2_loc (loc, PLUS_EXPR, arg0_type, + n_low, build_int_cst (arg0_type, -1)); + n_low = build_zero_cst (arg0_type); + in_p = !in_p; + } + } + *p_low = n_low; *p_high = n_high; *p_in_p = in_p; diff --git a/gcc/testsuite/g++.dg/torture/pr105189.C b/gcc/testsuite/g++.dg/torture/pr105189.C new file mode 100644 index 000000000000..a3870772cfe2 --- /dev/null +++ b/gcc/testsuite/g++.dg/torture/pr105189.C @@ -0,0 +1,19 @@ +// PR tree-optimization/105189 +// { dg-do run } + +int +foo () +{ + return -1; +} + +int +main () +{ + int c = foo () >= 0U && 1; + if (c != 1) + __builtin_abort (); + int d = foo () >= 3U && 1; + if (d != 1) + __builtin_abort (); +} -- 2.43.0