🚀 go-pugleaf

When compiling the following code, gcc emits a call to mcount that
trashes register 2 (the value return register).  What's wrong here?

MC8 /usr0/cmaeda : cat testgcc.c
struct xxx {
  struct xxx *next;
  struct xxx *prev;
  int data;
} foo;

void
function()
{
  foo.next = foo.prev = &foo;
}
MC8 /usr0/cmaeda : gcc -v -S -O -pg testgcc.c
Reading specs from /usr/misc/.gnu-comp/lib/gcc-lib/mips-dec-mach/2.3.1/specs
gcc version 2.3.1
 /usr/misc/.gnu-comp/lib/gcc-lib/mips-dec-mach/2.3.1/cpp -lang-c -v -iprefix /afs/cs.cmu.edu/project/mach3/latest/release/@sys/lib/gcc-mips-dec-mach/2.3.1/ -undef -D__GNUC__=2 -D__ANSI_COMPAT -DMIPSEL -DR3000 -DSYSTYPE_BSD -Dbsd4_2 -Dhost_mips -Dmips -Dpmax -Dunix -DMACH -DCMU -DCMUCS -DMTXINU -D__ANSI_COMPAT -D__MIPSEL__ -D__R3000__ -D__SYSTYPE_BSD__ -D__bsd4_2__ -D__host_mips__ -D__mips__ -D__pmax__ -D__unix__ -D__MACH__ -D__CMU__ -D__CMUCS__ -D__MTXINU__ -D__ANSI_COMPAT -D__MIPSEL -D__R3000 -D__SYSTYPE_


BSD -D__bsd4_2 -D__host_mips -D__mips -D__pmax -D__unix -D__MACH -D__CMU -D__CMUCS -D__MTXINU -D__OPTIMIZE__ -D__LANGUAGE_C__ -D__LANGUAGE_C -DLANGUAGE_C testgcc.c /usr/tmp/cc000517.i
GNU CPP version 2.3.1 [AL 1.1, MM 28] DECstation running Mach
 /usr/misc/.gnu-comp/lib/gcc-lib/mips-dec-mach/2.3.1/cc1 /usr/tmp/cc000517.i -mgpopt -quiet -dumpbase testgcc.c -O -version -p -o testgcc.s
GNU C version 2.3.1 [AL 1.1, MM 28] DECstation running Mach compiled by GNU C version 2.3.1.
MC8 /usr0/cmaeda : cat testgcc.s
        .file   1 "testgcc.c"
        .set    nobopt

 # GNU C 2.3.1 [AL 1.1, MM 28] DECstation running Mach compiled by GNU C

 # Cc1 defaults:

 # Cc1 arguments (-G value = 8, Cpu = default, ISA = 1):
 # -mgpopt -quiet -dumpbase -O -version -p -o

gcc2_compiled.:
        .space  4
        .text
        .align  2
        .globl  function

        .comm   foo,16

        .text

        .loc    1 10
        .ent    function
function:
        .frame  $sp,0,$31               # vars= 0, regs= 0/0, args = 0, extra= 0
        .mask   0x00000000,0
        .fmask  0x00000000,0
        la      $2,foo
        .data
        .align  2
$LP1:
        .word   0
        .text
        .set    noreorder
        .set    noat
        move    $1,$31          # save current return address
        jal     _mcount
        subu    $sp,$sp,8               # _mcount pops 2 words from  stack
        .set    reorder
        .set    at
        sw      $2,4($2)
        .set    noreorder
        .set    nomacro
        j       $31
        sw      $2,0($2)
        .set    macro
        .set    reorder

        .end    function