[llvm-commits] two-byte return optimization for AMD

[Evan Cheng]

I am not crazy about adding a subtarget feature for a micro- 
optimization. If you want to enable a family of optimizations for AMD  
chips, please just add something like a FeatureAMD feature.

Also, it seems awfully expensive to perform a full machine function  
pass. This seems like something that can be done at instruction  
selection time?

Evan

On Dec 7, 2008, at 12:19 AM, Nick Lewycky wrote:

> The AMD optimization manual suggests avoiding branches to 'ret'  
> instructions, preferring to emit 'rep; ret'. The attached patch  
> implements this.
>
> This doesn't apply very often across llvm-test. The largest is  
> kimwitu++ which produces 28 of these two-byte rets. The performance  
> impact seems to be less than noise, at least on my system.
>
> Please review!
>
> Nick
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