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From: Jakub Jelinek <jakub@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-6580] range-op-float: Extend lhs by 0.5ulp rather than 1ulp if not -frounding-math [PR109008] Date: Fri, 10 Mar 2023 11:41:06 +0000 (GMT) [thread overview] Message-ID: <20230310114106.053233858D1E@sourceware.org> (raw) https://gcc.gnu.org/g:44f80a370b76fd1564e280f08d6640d0f641d487 commit r13-6580-g44f80a370b76fd1564e280f08d6640d0f641d487 Author: Jakub Jelinek <jakub@redhat.com> Date: Fri Mar 10 12:40:23 2023 +0100 range-op-float: Extend lhs by 0.5ulp rather than 1ulp if not -frounding-math [PR109008] This patch, incremental to the just posted one, improves the reverse operation ranges significantly by widening just by 0.5ulp in each direction rather than 1ulp. Again, REAL_VALUE_TYPE has both wider exponent range and wider mantissa precision (160 bits) than any supported type, this patch uses the latter property. The patch doesn't do it if -frounding-math, because then the rounding can be +-1ulp in each direction depending on the rounding mode which we don't know, or for IBM double double because that type is just weird and we can't trust in sane properties. I've performed testing of these 2 patches on 300000 random tests as with yesterday's patch, exact numbers are in the PR, but I see very significant improvement in the precision of the ranges while keeping it conservatively correct. 2023-03-10 Jakub Jelinek <jakub@redhat.com> PR tree-optimization/109008 * range-op-float.cc (float_widen_lhs_range): If not -frounding-math and not IBM double double format, extend lhs range just by 0.5ulp rather than 1ulp in each direction. Diff: --- gcc/range-op-float.cc | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc index 58606aa4611..204b3911cc4 100644 --- a/gcc/range-op-float.cc +++ b/gcc/range-op-float.cc @@ -2205,8 +2205,8 @@ zero_to_inf_range (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, int signbit_known) [1., 1.] = op1 + [1., 1.]. op1's range is not [0., 0.], but [-0x1.0p-54, 0x1.0p-53] (when not -frounding-math), any value for which adding 1. to it results in 1. after rounding to nearest. - So, for op1_range/op2_range extend the lhs range by 1ulp in each - direction. See PR109008 for more details. */ + So, for op1_range/op2_range extend the lhs range by 1ulp (or 0.5ulp) + in each direction. See PR109008 for more details. */ static frange float_widen_lhs_range (tree type, const frange &lhs) @@ -2230,6 +2230,14 @@ float_widen_lhs_range (tree type, const frange &lhs) lb = dconstm1; SET_REAL_EXP (&lb, FLOAT_MODE_FORMAT (TYPE_MODE (type))->emax + 1); } + if (!flag_rounding_math && !MODE_COMPOSITE_P (TYPE_MODE (type))) + { + /* If not -frounding-math nor IBM double double, actually widen + just by 0.5ulp rather than 1ulp. */ + REAL_VALUE_TYPE tem; + real_arithmetic (&tem, PLUS_EXPR, &lhs.lower_bound (), &lb); + real_arithmetic (&lb, RDIV_EXPR, &tem, &dconst2); + } } if (real_isfinite (&ub)) { @@ -2240,6 +2248,14 @@ float_widen_lhs_range (tree type, const frange &lhs) ub = dconst1; SET_REAL_EXP (&ub, FLOAT_MODE_FORMAT (TYPE_MODE (type))->emax + 1); } + if (!flag_rounding_math && !MODE_COMPOSITE_P (TYPE_MODE (type))) + { + /* If not -frounding-math nor IBM double double, actually widen + just by 0.5ulp rather than 1ulp. */ + REAL_VALUE_TYPE tem; + real_arithmetic (&tem, PLUS_EXPR, &lhs.upper_bound (), &ub); + real_arithmetic (&ub, RDIV_EXPR, &tem, &dconst2); + } } /* Temporarily disable -ffinite-math-only, so that frange::set doesn't reduce the range back to real_min_representable (type) as lower bound
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