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

[Gary Funck <gary at intrepid dot com>]

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.