This occurs when building the UW IMAP toolkit on Sparc (it compiles on i386
and alpha).  I have a workaround in place, so this is not that urgent. 
I'll attach a .i file which breaks (mbx.i.sparc), and one with a workaround
(mbx.i.good).  The compile:

[prospector@lisa c-client]$ cc -g -O2 -m32 -mtune=ultrasparc -fPIC
-I/usr/kerberos/include -I/usr/include/openssl   -c -o mbx.o mbx.c -v
--save-temps
Reading specs from /usr/lib/gcc-lib/sparc64-redhat-linux/2.96/specs
gcc version 2.96 20000731 (Red Hat Linux 7.0)
 /usr/lib/gcc-lib/sparc64-redhat-linux/2.96/cpp0 -lang-c -v
-I/usr/kerberos/include -I/usr/include/openssl -D__GNUC__=2
-D__GNUC_MINOR__=96 -D__GNUC_PATCHLEVEL__=0 -D__ELF__ -Dunix -D_LONGLONG
-D__sparc__ -Dlinux -D__ELF__ -D__unix__ -D_LONGLONG -D__sparc__
-D__linux__ -D__unix -D__linux -Asystem(unix) -Asystem(posix)
-D__OPTIMIZE__ -g -D__SIZE_TYPE__=unsigned int -D__PTRDIFF_TYPE__=int
-D__GCC_NEW_VARARGS__ -Acpu(sparc) -Amachine(sparc) -D__PIC__ -D__pic__
mbx.c mbx.i
GNU CPP version 2.96 20000731 (Red Hat Linux 7.0) (cpplib)
 (sparc64 GNU/Linux with ELF)
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory "/usr/sparc64-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/kerberos/include
 /usr/include/openssl
 /usr/lib/gcc-lib/sparc64-redhat-linux/2.96/include
 /usr/include
End of search list.
 /usr/lib/gcc-lib/sparc-redhat-linux/2.96/cc1 mbx.i -gstabs+ -quiet
-dumpbase mbx.c -m32 -mtune=ultrasparc -g -O2 -version -fPIC -o mbx.s
GNU C version 2.96 20000731 (Red Hat Linux 7.0) (sparc-redhat-linux)
compiled by GNU C version 2.96 20000731 (Red Hat Linux 7.0).
mbx.c: In function `mbx_hdrpos':
mbx.c:1371: Unrecognizable insn:
(insn 116 114 118 (set (reg:SI 135)
        (minus:SI (const_int 4 [0x4])
            (const_int -4096 [0xfffff000]))) -1 (nil)
    (expr_list:REG_EQUAL (const_int 4100 [0x1004])
        (nil)))
mbx.c:1371: Internal compiler error in extract_insn, at recog.c:2108
Please submit a full bug report.