On Mon, Aug 17, 2015 at 5:44 PM, Richard Henderson <[email protected]> wrote: > On 08/17/2015 04:35 AM, Artyom Tarasenko wrote: >> Hi Richard, >> >> this patch seems to break a build when USE_LIVENESS_ANALYSIS is undefined. > > I suppose that's possible. If so, it must be a trivial error somewhere. > Why in the world would you want !USE_LIVENESS_ANALYSIS? > > Are you simply trying to see what sort of performance impact it has? I can > tell you it's fairly important for generating x86 code. The two operand > nature > of the ISA means that if we don't know that the source operand is dead, we > often have to introduce an extra move to preserve it.
~ a year ago there was a report that !USE_LIVENESS_ANALYSIS brings 5% speed improvement when running qemu-system-sparc64 . I'd like to see how does it look today. I see tcg_liveness_analysis taking 3%-5% in a perf top output, on the other hand the produced code must be more efficient, so it's interesting to see how does it sum up. Artyom -- Regards, Artyom Tarasenko SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu
