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Changing mips-elf-as behavior on delayed branches

Thiemo Seufer ths@networkno.de
Mon Jun 25 13:19:00 GMT 2007 
nkavv@physics.auth.gr wrote:
> Hi fellow binutilers
> 
> i have to comment on something that caught me by surprise. The binutils MIPS
> target (actually for binutils-2.15.94 of a build for a no-cost development
> environment) does not provide any options on delayed branching.
>
> The "mips-elf-as" assembler supposes that what is ALWAYS targeted is a MIPS
> microarchitecture with delayed branches (this applies for example for -mips1
> and -mips32). It does not even provide the option to switch this assumption
> off. At first i expected that there would exist something close to the gcc
> option (-fno-delayed-branch) that is resolved by gcc RTL emission. But is seems
> impossible to the assembler making the decision.

ISTR that version had already -O0 (and -g) implying no swapped branches.

> I work on embedded systems (embedded processor architecture) since 2000 and i
> always thought that delayed branching is a bad-to-the-bone design practice.

It also makes a CPU a lot faster without having to pay the cost of a branch
predictor. :-)


Thiemo
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