https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104674
Bug ID: 104674
Summary: i686 sse2: The two results of __divmoddi4 are mixed up
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: xavier.leroy at inria dot fr
Target Milestone: ---
Created attachment 52505
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52505&action=edit
Repro case
Configuration: GCC 11.2.0 configured for i686-pc-cygwin, as packaged by Cygwin,
running under Cygwin.
When compiled with
gcc -O2 -mfpmath=sse -msse2
the attached repro case incorrectly prints
888888.08889
The correct result is 888888.00000.
"gcc -O2" and "gcc -O1 -mfpmath=sse -msse2" produce the correct result.
Looking at the assembly code generated by "gcc -O2 -mfpmath=sse -msse2", we see
that the two results of __divmoddi4 (the quotient and the remainder) end up
stored at the same stack location:
leal 40(%esp), %eax <-- address where to store the remainder
movl 68(%esp), %edx
movl $10000000, 8(%esp)
movl %eax, 16(%esp)
movl 64(%esp), %eax
movl $0, 12(%esp)
movl %eax, (%esp)
movl %edx, 4(%esp)
call ___divmoddi4 <-- quotient is in edx:eax
movsd LC1, %xmm2
movd %eax, %xmm0
movd %edx, %xmm3
punpckldq %xmm3, %xmm0 <-- quotient is in xmm0
movq %xmm0, 40(%esp) <-- overwrites the remainder
Regards,
- Xavier Leroy
