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From: "Paul Edwards" <mutazilah@gmail.com>
To: "Richard Guenther" <richard.guenther@gmail.com>
Cc: <gcc@gcc.gnu.org>
Subject: Re: i370 port - music/sp - possible generic gcc problem
Date: Sun, 29 Nov 2009 14:31:00 -0000
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Latest information - 

> Ok, based on this, I traced it back further:
> 
> rtx
> gen_rtx_fmt_e0 (code, mode, arg0)
>     RTX_CODE code;
>     enum machine_mode mode;
>     rtx arg0;
> {
>  rtx rt;
>  rt = ggc_alloc_rtx (2);
>  memset (rt, 0, sizeof (struct rtx_def) - sizeof (rtunion));

The request for 2 (I guess, rtx's) results in a malloc for 65536
bytes, so presumably each rtx is 32k.  It appears that only the 
single byte at offset 47072 needs to be initialized to some
appropriate value (I found that x'08' and x'81' also work, and
I am still experimenting on that) in order to circumvent the 
problem of garbage code generation.

> rtx
> gen_rtx_MEM (mode, addr)
>     enum machine_mode mode;
>     rtx addr;
> {
>  rtx rt = gen_rtx_raw_MEM (mode, addr);
> 
>  /* This field is not cleared by the mere allocation of the rtx, so
>     we clear it here.  */
>  MEM_ATTRS (rt) = 0;
> 
>  return rt;
> }

I wonder if another field like the above also needs to be
initialized?  Or maybe the same field, but it needs to be
for the second rtx?

I will try to see if I can map that offset onto a meaningful variable.

BFN.  Paul.