[PATCH] Stop putting operations after a tail call

[Tim Northover]

Ping?

On Tue, Jul 2, 2013 at 8:25 PM, Tim Northover <t.p.northover at gmail.com> wrote:
> Hi,
>
> compnerd recently pointed out a disturbingly trivial failure when
> enabling tail calls on ARM Linux targets (though fortunately probably
> inaccessible from clang):
>
>     declare i8* @g(i8*)
>
>     define i8* @f(i8* %a) {
>     entry:
>       %0 = tail call i8* @g(i8* %a)
>       ret i8* %0
>     }
>
> When compiled at -O0 this hits an assertion failure[1]. There are many
> steps along the way, but I think the first objectively wrong decision
> is putting a tokenfactor for vreg exports (and hence possibly other
> operations) after the TC_RETURN instruction.
>
> The attached patch simply forgets about any pending vreg exports when
> a tail-call is encountered. Intuitively this seems like right (or at
> least harmless) behaviour, but I'm not familiar enough with FastISel
> to be sure.
>
> Does it seem reasonable?
>
> Cheers.
>
> Tim.
>
> [1] Via Schroedinger's FastISel; not supported on Thumb Linux but
> still gets vregs set ready for it.
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