registered var being stored/loaded from stack

[baver <baver at thebeever dot com>]

HI all,

Not sure if this fits in more with GCC or binutils.

We have amodified binutils/gcc to add a few opcodes to the MIPS-I ISA for a processor we've designed as part of our academics. One of these opcodes writes an index into a register we specify.

This works, but we're seeing

1) the value of the register before we write to it getting stored on the stack

2) our opcode loading the correct value into the register

3) the value then being read back from the stack instead of the register

 when we use any optimizations above -O0.

A sample code listing is at the bottom of the email, as well as the lines we've added to opcodes/mips-opc.c for our opcodes.

 

Anyone know how to stop the register from being stored and read from on the stack? We've defined it as

volatile register int idx asm("s0");

 

Thanks,

Richard

 

mips-opc.c:

const struct mips_opcode mips_builtin_opcodes[] =
{
{"spumov",  "d",    0x44000000, 0xffff07ff, WR_d,     0,      IK  },
{"setspu",  "j",    0x40000000, 0xffff0000, 0,      0,      IK  },
.....

 

 

code listing:

 

   1.
      500027a8:       afb0013c       sw    s0,316(sp)   <--------------- s0 is saved to stack
   2.
      500027ac:       24630001       addiu v1,v1,1
   3.
      500027b0:       afa30130       sw    v1,304(sp)
   4.
      500027b4:       0000f021       move  s8,zero
   5.
      500027b8:       00001010       mfhi  v0
   6.
      500027bc:       00021042       srl   v0,v0,0x1
   7.
      500027c0:       24420001       addiu v0,v0,1
   8.
      500027c4:       00f00018       mult  a3,s0
   9.
      500027c8:       00001812       mflo  v1
  10.
      500027cc:       afa30140       sw    v1,320(sp)
  11.
      500027d0:       00021840       sll   v1,v0,0x1
  12.
      500027d4:       00621821       addu  v1,v1,v0
  13.
      500027d8:       afa30144       sw    v1,324(sp)
  14.
      500027dc:       40000007       setspu        7
  15.
      500027e0:       44008000       spumov        s0   <-------------- We change value of s0
  16.
      500027e4:       8fa4017c       lw    a0,380(sp)
  17.
      500027e8:       8fa50130       lw    a1,304(sp)
  18.
      500027ec:       8fa6013c       lw    a2,316(sp)   <-------------- s0 is loaded from stack