pkg/55841: Mowitz: mfpmath=sse segfaults on gcc10/i386

[jbryn%students.wcpss.net@localhost]

>Number:         55841
>Category:       pkg
>Synopsis:       Mowitz: mfpmath=sse segfaults on gcc10/i386
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Dec 05 08:25:00 +0000 2020
>Originator:     Jackson Bryn
>Release:        NetBSD-current 9.99.76
>Organization:
N/A
>Environment:
build.localdomain 9.99.76 NetBSD 9.99.76 (GENERIC) #0: Mon Nov 30 07:53:42 UTC 2020  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/i386/compile/GENERIC i386
>Description:
Mowitz segfaults in draw_segment due to SSE optimization causing undefined behavior. Tested this on a Haswell CPU in 32-bit mode, VMWare.
>How-To-Repeat:
Install siag and Mowitz with mfpmath=sse (also used -O2, march/mtune=bonnell, and -fomit-frame-pointer + -pipe). Make sure to use lang/gcc10 to give exact reproduction.
>Fix:
Workaround is to just force -mfpmath to 387.