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From: Aldy Hernandez <aldyh@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-2225] [ranger] x == -0.0 does not mean we can replace x with -0.0 Date: Fri, 26 Aug 2022 16:14:07 +0000 (GMT) [thread overview] Message-ID: <20220826161407.2D24838515ED@sourceware.org> (raw) https://gcc.gnu.org/g:d085901e0e3b3d490fb756b3e939750e7ea2b7fc commit r13-2225-gd085901e0e3b3d490fb756b3e939750e7ea2b7fc Author: Aldy Hernandez <aldyh@redhat.com> Date: Fri Aug 26 16:55:52 2022 +0200 [ranger] x == -0.0 does not mean we can replace x with -0.0 On the true side of x == -0.0, we can't just blindly value propagate the -0.0 into every use of x because x could be +0.0. With this change, we only allow the transformation if !HONOR_SIGNED_ZEROS or if the range is known not to contain 0. gcc/ChangeLog: * range-op-float.cc (foperator_equal::op1_range): Do not blindly copy op2 range when honoring signed zeros. Diff: --- gcc/range-op-float.cc | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc index ad2fae578d2..ff9fe312acf 100644 --- a/gcc/range-op-float.cc +++ b/gcc/range-op-float.cc @@ -252,8 +252,21 @@ foperator_equal::op1_range (frange &r, tree type, switch (get_bool_state (r, lhs, type)) { case BRS_TRUE: - // If it's true, the result is the same as OP2. - r = op2; + if (HONOR_SIGNED_ZEROS (type) + && op2.contains_p (build_zero_cst (type))) + { + // With signed zeros, x == -0.0 does not mean we can replace + // x with -0.0, because x may be either +0.0 or -0.0. + r.set_varying (type); + } + else + { + // If it's true, the result is the same as OP2. + // + // If the range does not actually contain zeros, this should + // always be OK. + r = op2; + } // The TRUE side of op1 == op2 implies op1 is !NAN. r.set_nan (fp_prop::NO); break;
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