Simon Kagstrom <simon.kagstrom@xxxxxx> writes:
> So, I used the -fno-delayed-branch instruction when compiling, which
> is documented as
>
> If supported for the target machine, attempt to reorder
> instructions to exploit instruction slots available after delayed
> branch instructions.
>
> I use GCC 3.4.4 from the emdebian project,
>
> mips-linux-gcc (GCC) 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)
>
> -fno-delayed-branch seems to mostly work, i.e., I get code as
>
> 10001d0: 27a40010 addiu a0,sp,16
> 10001d4: 0c400008 jal 1000020 <game_loop>
> 10001d8: 00000000 nop
>
> which is what I want. However, on conditional branches, it doesn't
> work as expected:
>
> 1000160: 8c670000 lw a3,0(v1)
> 1000164: 24020013 li v0,19
> 1000168: 0000000c syscall
> 100016c: 25080001 addiu t0,t0,1
> 1000170: 29020018 slti v0,t0,24
> 1000174: 1440fff9 bnez v0,100015c <game_init+0x7c>
> 1000178: 24630060 addiu v1,v1,96
>
> Here, I would have expected that the addiu would go before bnez, and
> that a nop is inserted after the branch.
>
>
> So the question is if this is the intended behavior, or if it simply
> is a bug with the -fno-delayed-branch implementation?
This looks like a bug to me. You may want to open a bug report; see
http://gcc.gnu.org/bugs.html
I suspect the bug is that -fdelayed-branch is failing to pass -O0 to
the assembler. Try compiling with -Wa,-O0.
Ian
