[LLVMdev] Google's Go

[John McCall]

Jon Harrop wrote:
> On Thursday 19 November 2009 19:48:18 Owen Anderson wrote:
>   
>> On Nov 19, 2009, at 10:25 AM, Jon Harrop wrote:
>>     
>>>> In this case, the assertion that LLVM is slow is correct: it's
>>>> definitely slower than a non-optimizing compiler.
>>>>         
>>> I'm *very* surprised by this and will test it myself...
>>>       
>
> I've tested it and LLVM is indeed 2x slower to compile, although it generates 
> code that is 2x faster to run...
>
>   
>> Compared to a compiler in the same category as PCC, whose pinnacle of
>> optimization is doing register allocation?  I'm not surprised at all.
>>     
>
> What else does LLVM do with optimizations turned off that makes it slower?
>   

My guess would be primarily (1) respectable instruction selection, 
followed by (2) good register allocation.  But at some point, the 
overhead of going through an abstract IR will slow you down.  You're 
never going to beat a splat compiler except with another splat compiler.

John.
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