[Bug c/16584] New: -msse2 also enabling -mfpmath=sse option causing illegal instruction errors

["aron-gcc at sightspeed dot com" <gcc-bugzilla at gcc dot gnu dot org>]

The gcc command line option -msse2 seems to be implicitly turning on the -
mfpmath=sse option. The man pages describe the -msse2 as only enabling the use 
of SSE2 intrinsics rather than automatic use.

This bug is very dangorous since it breaks using runtime detection of SSE2 
support. We use the -msse2 option to only generate SSE2 code in areas where we 
have written intrinsics so that a single binary is platform safe.

A simple example is:
gcc -msse2 test.c

<file test.c>
int main(void)
{
        int i = 1;
        float temp2 = 1.0 * (i*i); // Allow for an optimal sse2 int to float 
conversion

        return 0;
}

<test.s> output

        .file   "test.c"
        .text
.globl main
        .type   main, @function
main:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $24, %esp
        andl    $-16, %esp
        movl    $0, %eax
        addl    $15, %eax
        addl    $15, %eax
        shrl    $4, %eax
        sall    $4, %eax
        subl    %eax, %esp
        movl    $1, -4(%ebp)
        movl    -4(%ebp), %eax
        imull   -4(%ebp), %eax
        cvtsi2sd        %eax, %xmm0
        cvtsd2ss        %xmm0, %xmm0
        movss   %xmm0, -8(%ebp)
        movl    $0, %eax
        leave
        ret
        .size   main, .-main
        .section        .note.GNU-stack,"",@progbits
        .ident  "GCC: (GNU) 3.4.0"

<end>
Note that the movss, cvtsi2sd and cvtsd2ss instructions are used which should 
not happen.
When this is compiled and run on a Pentium 3 machine a SIGILL is generated.



<Additional Information>
<file test.i>
# 1 "test.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test.c"
int main(void)
{
 int i = 1;
 float temp2 = 1.0 * (i*i);

 return 0;
}
<end file>



Reading specs from /usr/lib/gcc/i486-slackware-linux/3.4.0/specs
Configured with: ../gcc-3.4.0/configure --prefix=/usr --enable-shared --enable-
threads=posix --enable-__cxa_atexit --disable-checking --with-gnu-ld --verbose -
-target=i486-slackware-linux --host=i486-slackware-linux
Thread model: posix
gcc version 3.4.0
 /usr/libexec/gcc/i486-slackware-linux/3.4.0/cc1 -E -quiet -v test.c -msse2 -
mtune=i486 -o test.i
ignoring nonexistent directory "/usr/lib/gcc/i486-slackware-
linux/3.4.0/../../../../i486-slackware-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc/i486-slackware-linux/3.4.0/include
 /usr/include
End of search list.
 /usr/libexec/gcc/i486-slackware-linux/3.4.0/cc1 -fpreprocessed test.i -quiet -
dumpbase test.c -msse2 -mtune=i486 -auxbase test -version -o test.s
GNU C version 3.4.0 (i486-slackware-linux)
        compiled by GNU C version 3.4.0.
GGC heuristics: --param ggc-min-expand=64 --param ggc-min-heapsize=64518
 /usr/lib/gcc/i486-slackware-linux/3.4.0/../../../../i486-slackware-
linux/bin/as -V -Qy -o test.o test.s
GNU assembler version 2.15.90.0.3 (i486-slackware-linux) using BFD version 
2.15.90.0.3 20040415
 /usr/libexec/gcc/i486-slackware-linux/3.4.0/collect2 --eh-frame-hdr -m 
elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/gcc/i486-slackware-
linux/3.4.0/../../../crt1.o /usr/lib/gcc/i486-slackware-
linux/3.4.0/../../../crti.o /usr/lib/gcc/i486-slackware-linux/3.4.0/crtbegin.o -
L/usr/lib/gcc/i486-slackware-linux/3.4.0 -L/usr/lib/gcc/i486-slackware-
linux/3.4.0 -L/usr/lib/gcc/i486-slackware-linux/3.4.0/../../../../i486-
slackware-linux/lib -L/usr/lib/gcc/i486-slackware-linux/3.4.0/../../.. test.o -
lgcc -lgcc_eh -lc -lgcc -lgcc_eh /usr/lib/gcc/i486-slackware-
linux/3.4.0/crtend.o /usr/lib/gcc/i486-slackware-linux/3.4.0/../../../crtn.o

Also tested and found under gcc-3.3.4

-- 
           Summary: -msse2 also enabling -mfpmath=sse option causing illegal
                    instruction errors
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: aron-gcc at sightspeed dot com
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16584