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- Subject: Re: Computed goto optimization of vanilla Lua
- From: Roberto Ierusalimschy <roberto@...>
- Date: Fri, 5 Feb 2016 09:51:25 -0200
> On 04/02/16 12:45, Roberto Ierusalimschy wrote:
> > These macros are there exactly for this reason. However, my ealier
> > tests (a few years ago, when we introduced the macros) did not show
> > any perceptible improvement. In particular, the GCC compiler insisted
> > in applying a space optimization that merged the common code at the
> > end of different branches in a conditional (most of 'vmbreak', in our
> > case), therefore throwing away any possibility of optimized branch
> > predictions. (All opcodes ended up using the same indirect jump in the
> > final code.) I will try it again.
> Did you compile the code with '-fno-gcse -fno-crossjumping'?
As I said, I used 'gcc -O2'. I will try these.