[PATCH, libitm]: Optimize x86_64 gtm_jmpbuf layout

[Uros Bizjak <ubizjak at gmail dot com>]

Hello!

Attached patch optimizes x86_64 gtm_jmpbuf layout to avoid copying
return address. Optimized layout uses the same trick as x86_32 - call
used registers are saved just below return address. And there is just
enough space in the call alignment hole to put all of them there.

2012-01-24  Uros Bizjak  <ubizjak@gmail.com>

	* config/x86/target.h (gtm_jmpbuf) [__x86_64__]: Move rip to the
	end of struct.
	* config/x86/sjlj.S (_ITM_beginTransaction) [__x86_64__]: Update
	offset values.  Do not copy return address.  Decrement stack
	by 56 bytes only.
	(GTM_longjump) [__x86_64__]: Update offset values.

Tested on x86_64-pc-linux-gnu.

OK for mainline?

BTW: Do we really need move at the end of GTM_longjump:

	movq	48(%rsi), %r15
	movq	56(%rsi), %rdx
>>	movl	%edi, %eax
	cfi_def_cfa(%rcx, 0)
	cfi_register(%rip, %rdx)
	movq	%rcx, %rsp
	jmp	*%rdx

Uros.

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