From: Aldy Hernandez <aldyh@redhat.com>
To: GCC patches <gcc-patches@gcc.gnu.org>
Cc: Jakub Jelinek <jakub@redhat.com>,
Andrew MacLeod <amacleod@redhat.com>,
Aldy Hernandez <aldyh@redhat.com>
Subject: [PATCH] [ranger] x == -0.0 does not mean we can replace x with -0.0
Date: Fri, 26 Aug 2022 17:46:06 +0200 [thread overview]
Message-ID: <20220826154606.1155977-1-aldyh@redhat.com> (raw)
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 (or vice versa).
With this change, we only allow the transformation if
!HONOR_SIGNED_ZEROS or if the range is known not to contain 0.
Will commit after tests complete.
gcc/ChangeLog:
* range-op-float.cc (foperator_equal::op1_range): Do not blindly
copy op2 range when honoring signed zeros.
---
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;
--
2.37.1
next reply other threads:[~2022-08-26 15:46 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-26 15:46 Aldy Hernandez [this message]
2022-08-26 16:40 ` Jakub Jelinek
2022-08-29 13:13 ` Aldy Hernandez
2022-08-29 13:21 ` Jakub Jelinek
2022-08-29 13:31 ` Aldy Hernandez
2022-08-29 14:20 ` Jeff Law
2022-08-29 14:26 ` Aldy Hernandez
2022-08-29 15:08 ` Jeff Law
2022-08-29 15:13 ` Toon Moene
2022-08-29 17:07 ` Jeff Law
2022-08-29 17:37 ` Koning, Paul
2022-08-29 19:04 ` Toon Moene
2022-08-29 15:29 ` Aldy Hernandez
2022-08-31 10:08 ` Aldy Hernandez
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