Re: [PATCH] mm/pg-r4k.c: Dump the generated code

[Nigel Stephens <nigel@mips.com>]

Franck Bui-Huu wrote:
> Thiemo Seufer wrote:
>   
>> Could you check what "-march=mips32r2 -smartmips -mtune=4ksd" does?
>> I expect it to have the same result than "-march=4ksd".
>>
>>     
>
> OK, I give it a try and here are some figures:
>
> $ mipsel-linux-size mipssde-6.05.00-20061023/vmlinux~*
>    text    data     bss     dec     hex filename
> 1446130   58456   93056 1597642  1860ca mipssde-6.05.00-20061023/vmlinux~4ksd
> 1472034   58456   93056 1623546  18c5fa mipssde-6.05.00-20061023/vmlinux~mips32r2-smartmips
> 1446130   58456   93056 1597642  1860ca mipssde-6.05.00-20061023/vmlinux~mips32r2-smartmips-mtune4ksd
>
> So you're right "-march=mips32r2 -smartmips -mtune=4ksd" gives the
> same result as "-march=4ksd"
>
>   

IIRC that should be -msmartmips, not -smartmips.

> And the extra space given by "-march=mips32r2 -smartmips" is coming
> from some additional nop instructions:
>
> $ mipsel-linux-objdump -D vmlinux~mips32r2-smartmips > vmlinux~mips32r2-smartmips.S
> $ mipsel-linux-objdump -D vmlinux~4ksd > vmlinux~4ksd.S
> $ grep -c nop *.S
> vmlinux~4ksd.S:18708
> vmlinux~mips32r2-smartmips.S:27895
>
> It seems that these extra nops are used for load delays. For example:
>
> vmlinux~4ksd.S:
> --------------
> <snip>
> c00008b4:      8fa40040        lw      a0,64(sp)
> c00008b8:      27a40018        addiu   a0,sp,24
> c00008bc:      0c000148        jal     c0000520 <try_name>
> <snip>
>
> vmlinux~mips32r2-smartmips.S:
> ---------------------------
> c00008b8:      8fa40040        lw      a0,64(sp)
> c00008bc:      00000000        nop
> c00008c0:      27a40018        addiu   a0,sp,24
> c00008c4:      0c000148        jal     c0000520 <try_name>
>
>   

That's weird: load delay slots should only be required by -march=mips1 
(or no -march)

Are you sure that the -march=mips32r2 option is really getting passed to 
the compiler and assembler?

Nigel