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Re: [RFC] Clean up SSE variable shifts

From: Richard Henderson <rth at twiddle dot net>
To: "Lu, Hongjiu" <hongjiu dot lu at intel dot com>
Cc: "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>
Date: Sat, 21 Aug 2010 15:25:18 -0700
Subject: Re: [RFC] Clean up SSE variable shifts
References: <4C6EF1B7.7020508@twiddle.net> <8EA2C2C4116BF44AB370468FBF85A7770179ACA2E4@orsmsx504.amr.corp.intel.com>

On 08/21/2010 01:28 PM, Lu, Hongjiu wrote:
>> (1) Instead of having the compiler generate a jump table, use a
>> computed branch inside inline assembly.
> 
> Have you compared the generated code against C version in varshift.h?

Yes, it removes a memory access from .rodata.

> What is the performance impact of extra function call
> vs. multiple copies of the same jump table?

I don't know.  I would hope that an indirect call and return
would be just as predictable as an indirect jump and branch.

Fancy helping me benchmark?

r~

Follow-Ups:
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References:
- [RFC] Clean up SSE variable shifts
  - From: Richard Henderson
- RE: [RFC] Clean up SSE variable shifts
  - From: Lu, Hongjiu

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