[PATCH, 4/16] Implement -foffload-alias
Wed Nov 11 10:53:00 GMT 2015
On Mon, 9 Nov 2015, Tom de Vries wrote:
> On 09/11/15 16:35, Tom de Vries wrote:
> > Hi,
> > this patch series for stage1 trunk adds support to:
> > - parallelize oacc kernels regions using parloops, and
> > - map the loops onto the oacc gang dimension.
> > The patch series contains these patches:
> > 1 Insert new exit block only when needed in
> > transform_to_exit_first_loop_alt
> > 2 Make create_parallel_loop return void
> > 3 Ignore reduction clause on kernels directive
> > 4 Implement -foffload-alias
> > 5 Add in_oacc_kernels_region in struct loop
> > 6 Add pass_oacc_kernels
> > 7 Add pass_dominator_oacc_kernels
> > 8 Add pass_ch_oacc_kernels
> > 9 Add pass_parallelize_loops_oacc_kernels
> > 10 Add pass_oacc_kernels pass group in passes.def
> > 11 Update testcases after adding kernels pass group
> > 12 Handle acc loop directive
> > 13 Add c-c++-common/goacc/kernels-*.c
> > 14 Add gfortran.dg/goacc/kernels-*.f95
> > 15 Add libgomp.oacc-c-c++-common/kernels-*.c
> > 16 Add libgomp.oacc-fortran/kernels-*.f95
> > The first 9 patches are more or less independent, but patches 10-16 are
> > intended to be committed at the same time.
> > Bootstrapped and reg-tested on x86_64.
> > Build and reg-tested with nvidia accelerator, in combination with a
> > patch that enables accelerator testing (which is submitted at
> > https://gcc.gnu.org/ml/gcc-patches/2015-10/msg01771.html ).
> > I'll post the individual patches in reply to this message.
> this patch addresses the problem that once the offloading region has been
> split off from the original function, alias analysis can no longer use
> information available in the original function that would allow it to do a
> more precise analysis for the offloading function. [ At some point we could
> use fipa-pta for that, as discussed in PR46032, but that's not feasible now. ]
> The basic idea behind the patch is that for typical usage, the base pointers
> used in an offloaded region are non-aliasing. The patch works by adding
> restrict to the types of the fields used to pass data to an offloading region.
> The patch implements a new option
> The option -foffload-alias=none instructs the compiler to assume that
> object references and pointer dereferences in an offload region do not
> The option -foffload-alias=pointer instructs the compiler to assume that
> objects references in an offload region do not alias.
> The option -foffload-alias=all instructs the compiler to make no
> assumptions about aliasing in offload regions.
> The default value is -foffload-alias=none.
I think global options for this is nonsense. Please follow what
we do for #pragma GCC ivdep for example, thus allow the alias
behavior to be specified per "region" (whatever makes sense here
in the context of offloading).
> - Tom
Richard Biener <email@example.com>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)
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