More embarrassing microbenchmars for D's GC.

[Walter Bright]

Leandro Lucarella wrote:
> But there are a few other results I can't explain:
> 1) Why is D gc (disabled or not) version ~25% slower than the D version
>    that uses malloc when iterating the list? It shouldn't be any GC
>    activity in that part. Could be some GC locallity issue that yields
>    more cache misses?

There are so many factors that can influence this, it's hard to say 
without spending a lot of time carefully examining it.

> 2) Why is D malloc version ~33% slower than the C version? I took a look
>    at the generated assembly and it's almost identical:
> 	<_Dmain+198>:   lea    -0x20(%ebp),%eax
> 	<_Dmain+201>:   lea    0x0(%esi,%eiz,1),%esi
> 	<_Dmain+208>:   addl   $0x1,0x8(%eax)
> 	<_Dmain+212>:   adcl   $0x0,0xc(%eax)
> 	<_Dmain+216>:   mov    (%eax),%eax
> 	<_Dmain+218>:   test   %eax,%eax
> 	<_Dmain+220>:   jne    0x804a240 <_Dmain+208>
> 
> 
> 	<main+248>:     lea    -0x1c(%ebp),%eax
> 	<main+251>:     nop
> 	<main+252>:     lea    0x0(%esi,%eiz,1),%esi
> 	<main+256>:     addl   $0x1,0x4(%eax)
> 	<main+260>:     adcl   $0x0,0x8(%eax)
> 	<main+264>:     mov    (%eax),%eax
> 	<main+266>:     test   %eax,%eax
> 	<main+268>:     jne    0x8048550 <main+256>
> 	<main+270>:     movl   $0x0,0x4(%esp)
> 	<main+278>:     movl   $0x8049800,(%esp)
> 
> Tests attached.

Without running a profiler, there's no way to be sure about just where 
in the code the time is being consumed.