This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug c/84190] New: [7 Regression] double arithmetic on x86 no longer rounds to nearest
- From: "bruno at clisp dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sat, 03 Feb 2018 10:54:22 +0000
- Subject: [Bug c/84190] New: [7 Regression] double arithmetic on x86 no longer rounds to nearest
- Auto-submitted: auto-generated
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84190
Bug ID: 84190
Summary: [7 Regression] double arithmetic on x86 no longer
rounds to nearest
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: bruno at clisp dot org
Target Milestone: ---
Created attachment 43331
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43331&action=edit
test program
The attached program foo.c tests whether simple 'double' arithmetic does
round-to-nearest. It uses 'volatile double' types to make sure that on x86,
x86_64, and ia64, only 53 bits of precision are used instead of the "extended"
doubles that have 64 bits of precision.
With gcc versions 4.2.4 to 6.4.0:
$ gcc -m32 -O -Wall foo.c && ./a.out
1 1 1 1
With gcc versions 7.1.0 to 7.3.0:
$ gcc -m32 -O -Wall foo.c && ./a.out
0 0 0 0
This occurs even with -frounding-math:
$ gcc -m32 -O -frounding-math -Wall foo.c && ./a.out
0 0 0 0
It does not occur when inlining is disabled:
$ gcc -m32 -O -fno-inline -Wall foo.c && ./a.out
1 1 1 1