Re: (gcc 4.2) how to create an ADDR_EXPR that refers to a linkage name?

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(gcc 4.2) how to create an ADDR_EXPR that refer...
\ Gary Funck (1 Sep 2007)
. \ Diego Novillo (1 Sep 2007)
. . \ Gary Funck (1 Sep 2007)

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Subject:	Re: (gcc 4.2) how to create an ADDR_EXPR that refers to a linkage name?
Group:	Gcc
From:	Gary Funck
Date:	1 Sep 2007

On Sat, Sep 01, 2007 at 01:43:37PM -0400, Diego Novillo wrote:
>
> Have you considered using the data sharing machinery in OpenMP? We
> simply create a data structure holding all shared variables, allocate
> that in shared memory and re-write all references to shared variables
> as dereferences to that structure.

Diego, thanks. Some other implmentations of UPC reference
all shared variables indirectly through a table, built
at runtime. The compiler tells the runtime how much space
each variable reauires, and the runtime alloctes this from
the shared memory region.

The current strategy used by GCC/UPC is somewhat simpler;
it lets the linker create the layout of the shared
variable section. Perhaps we need to re-visit this design
decision, and adopt a scheme similar to that used by GOMP.
I'll review omp-low.c for ideas.

GCC/UPC does have a pthreads mode of operation, but that is
a special case. UPC threads are usually mapped to separate
processes. The shared memory region is potentially
distributed across network nodes, often accessed via a
high speed interconnect. The runtime that is part of the
GCC/UPC's release supports only SMP configurations and
relies on mmap(). However, GCC/UPC also works with a more
general runtime developed by Berkeley, which supports many
network interconnects.

>
> This trick you are implementing with cloning the VAR_DECLs is
> guaranteed not to work, sorry. We very explicitly assume that if
> DECL_UID (x1) == DECL_UID (x2) then x1 == x2. This is not something
> that will change.

Yeah, I suspected as much when I first wrote that code.
I wasn't too surprised to see that it failed a consistency
check in GCC 4.2.