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Date: Thu, 11 May 2006 11:31:25 +0930
From: Alan Modra <amodra@bigpond.net.au>
To: Paul Mackerras <paulus@samba.org>
Subject: Re: [RFC/PATCH] Make powerpc64 use __thread for per-cpu variables
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On Thu, May 11, 2006 at 11:21:15AM +1000, Paul Mackerras wrote:
> Alan Modra writes:
> 
> > gcc shouldn't think there is any reason to cache the address.
> 
> Can I rely on that being true in the future?

It isn't true in the *present*, except with a compiler on my home
machine.  :-) 

__thread int i1;
void
f3 (void)
{
  int x = i1;
  __asm__ __volatile__ ("#dragons be here.  %0" : "+r" (x));
  i1 = x;
}

current mainline with -O2 -S -mtls-size=16

f3:
        addi 9,2,i1@tprel
        lwz 0,0(9)
#APP
        #dragons be here.  0
#NO_APP
        stw 0,0(9)
        blr

Same thing with my modified compiler.

f3:
        lwz 0,i1@tprel(2)
#APP
        #dragons be here.  0
#NO_APP
        stw 0,i1@tprel(2)
        blr

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre