Re: [PATCH] rs6000: Add "cannot_copy" attribute, use it (PR67788, PR67789)

[David Edelsohn <dje dot gcc at gmail dot com>]

On Thu, Oct 1, 2015 at 2:08 AM, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
> After the shrink-wrapping patches the prologue will often be pushed
> "deeper" into the function, which in turn means the software trace cache
> pass will more often want to duplicate the basic block containing the
> prologue.  This caused failures for 32-bit SVR4 with -msecure-plt PIC.
>
> This configuration uses the load_toc_v4_PIC_1 instruction, which creates
> assembler labels without using the normal machinery for that.  If now
> the compiler decides to duplicate the insn, it will emit the same label
> twice.  Boom.
>
> It isn't so easy to fix this to use labels the compiler knows about (let
> alone test that properly).  Instead, this patch wires up a "cannot_copy"
> attribute to be used by TARGET_CANNOT_COPY_P, and sets that attribute on
> these insns we do not want copied.
>
> Bootstrapped and tested on powerpc64-linux, with the usual configurations
> (-m32,-m32/-mpowerpc64,-m64,-m64/-mlra); new testcase fails before, works
> after (on 32-bit).
>
> Is this okay for mainline?

Is this expensive enough that it is worth limiting the definition of
the hook to configurations that include 32-bit SVR4 support so that
not every configuration incurs the overhead?

Thanks, David