optimizations

[Bonzini]

> > Could you please also tell me if 3.3 and 3.4 remove the extra mov's in
and out
> > of %eax. Ideally, there should be no more than 4 instructions in the
critical
> > loop.
>
> .L2:
> movl -4(%ebp), %eax <== still does the load
> cmpl $16, %eax
> je .L7
> incl %eax
> movl %eax, -4(%ebp) <== and store
> jmp .L2
> .L7:
>
> For some reason it is not (even with -fnew-ra), but on PPC there
> is no extra load/store.

Instruction counts do not tell the whole story; gcc is simply putting more
pressure on the decoding unit but less pressure on the execution unit (which
otherwise would execute two loads in the `taken' case).  Things might be
different if gcc is given other options like -mtune=i386.

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