adding -fnoalias ... would a patch be accepted ?

[torbenh]

On Tue, Jan 05, 2010 at 02:46:30PM +0100, Richard Guenther wrote:
> On Tue, Jan 5, 2010 at 2:40 PM, torbenh <torbenh@gmx.de> wrote:
> > __restrict__ is of no help here. which leads me to the question whats
> > the point of a restricted this pointer ? members of structs arent
> > unaliased by a __restrict__ pointer to the struct.
> >
> > my favourite solution would be __noalias__ ... msvc has that.
> > but -fnoalias would make me happy too.
> >
> > i havent read much of the gcc code yet, so i am not sure what i need to
> > patch.
> >
> > refs_may_alias_p_1() is my current bet though.
> 
> The -fno-alias-X things do not make much sense for user code (they
> have been historically used from Frontends).  If restrict doesn't work
> for you (do you have a testcase that can reproduce your issue?)
> then you probably need to wait for IPA pointer analysis to be
> fixed in GCC 4.6.

can you please explain, why you reject the idea of -fnoalias ? 
msvc has declspec(noalias) icc has -fnoalias 


ramp.cc attached.
compiling it with gcc -S -O3 ramp.cc on x86_64 yields:

------------------------------------------------------------
_Z11fill_bufferPfm:
.LFB1:
	testq	%rsi, %rsi
	je	.L1
	xorl	%eax, %eax
	movss	.LC0(%rip), %xmm2
	.align 16
.L3:
	movss	ramp(%rip), %xmm0
	movaps	%xmm0, %xmm1
	addss	%xmm2, %xmm1
	movss	%xmm1, ramp(%rip)
	movss	%xmm0, (%rdi,%rax,4)
	addq	$1, %rax
	cmpq	%rax, %rsi
	ja	.L3
.L1:
	rep
	ret
-----------------------------------------------------------


-- 
torben Hohn