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Subject: Re: [Qemu-devel] [PULL 5/7] tcg: Add mmu helpers that take a return
 address argument
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To: Aurelien Jarno <aurelien@aurel32.net>
Cc: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, anthony@codemonkey.ws

On 08/27/2013 03:46 AM, Aurelien Jarno wrote:
> On the other hand calling the helper is the exception more than the
> rule (that's why they have been moved at the end of the TB), so we 
> should not look to much at generating fast code, but rather small code
> in order to use the caches (both TB and CPU caches) more efficiently.
> 
> Therefore even on x86, if we move the -1 at the helper level, it should
> be possible to use a tail call for the stores, something like:
> 
>     mov    %r14,%rdi
>     mov    %ebx,%edx
>     xor    %ecx,%ecx
>     lea    -0x10f(%rip),%r8        # 0x7f2541a6f69a
>     pushq  %r8
>     jmpq   0x7f25526757a0
> 
> Instead of:
> 
>     mov    %r14,%rdi
>     mov    %ebx,%edx
>     xor    %ecx,%ecx
>     lea    -0x10f(%rip),%r8        # 0x7f2541a6f69a
>     callq  0x7f25526757a0
>     jmpq   0x7f2541a6f69b

Fair enough.  I'll have a go at some follow-ups then.


r~