Hi Andrew,
Andrew Stubbs wrote:
This is more-or-less what I was planning to do myself, but as I want
to include all the other features that get parametrized in gcn.cc,
gcn.h, gcn-hsa.h, gcn-opts.h, I hadn't got around to it yet.
Unfortunately, I think the gcn.opt and config.gcc will always need
manually updating, but if that's all it'll be an improvement.
Well, for .opt see how nvptx does it – it actually generates an .opt file.
I don't like the idea of including AMDGPU_ISA_UNSUPPORTED;
I concur – I was initially thinking of reporting the device name
("Unsupported %s") but I then realized that the agent returns a string
while only for GCC generated files (→ eflag) the hexcode is used. Thus,
I ended up not using it.
Ultimately, I want to replace many of the conditionals like
"TARGET_CDNA2_PLUS" from the code and replace them with feature flags
derived from a def file, or at least a header file. We've acquired too
many places where there are unsearchable conditionals that need
finding and fixing every time a new device comes along.
I was thinking of having more flags, but those where the only ones
required for the two files.
I had imagined that this .def file would exist in gcc/config/gcn, but
you've placed it in libgomp.... maybe it makes sense to have multiple
such files if they contain very different data, but I had imagined one
file and I'm not sure that the compiler definitions live in libgomp.
There is already:
gcc/config/darwin-c.cc:#include "../../libcpp/internal.h"
gcc/config/gcn/gcn-run.cc:#include
"../../../libgomp/config/gcn/libgomp-gcn.h"
gcc/fortran/cpp.cc:#include "../../libcpp/internal.h"
gcc/fortran/trigd_fe.inc:#include "../../libgfortran/intrinsics/trigd.inc"
But there is also the reverse:
libcpp/lex.cc:#include "../gcc/config/i386/cpuid.h"
libgfortran/libgfortran.h:#include "../gcc/fortran/libgfortran.h"
lto-plugin/lto-plugin.c:#include "../gcc/lto/common.h"
If you add more items, it is probably better to have it under
gcc/config/gcn/ - and I really prefer a single file for all.
* * *
Talking about feature sets: This would be a bit like LLVM (see below)
but I think they have a bit too much indirections. But I do concur that
we need to consolidate the current support – and hopefully make it
easier to keep adding more GPU support; we seem to have already covered
a larger chunk :-)
I also did wonder whether we should support, e.g., running a gfx1100
code (or a gfx11-generic one) on, e.g., a gfx1103 device. Alternatively,
we could keep the current check which requires an exact match.
BTW: I do note that looking at the feature sets in LLVM that all GFX110x
GPUs seem to have common silicon bugs: FeatureMSAALoadDstSelBug and
FeatureMADIntraFwdBug, while 1100 and 1102 additionally have the
FeatureUserSGPRInit16Bug but 1101 and 1103 don't. — For some reasons,
FeatureISAVersion11_Generic only consists of two of those bugs (it
doesn't have FeatureMADIntraFwdBug), which doesn't seem to be that
consistent. Maybe the workaround has issues elsewhere? If so, a generic
-march=gfx11 might be not as useful as one might hope for.
* * *
If I look at LLVM's
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AMDGPU/AMDGPU.td
,
they first define several features – like 'FeatureUnalignedScratchAccess'.
Then they combine them like in:
def FeatureISAVersion11_Common ... [FeatureGFX11, ...
FeatureAtomicFaddRtnInsts ...
And then they use those to map them to feature sets like:
def FeatureISAVersion11_0_Common ...
listconcat(FeatureISAVersion11_Common.Features,
[FeatureMSAALoadDstSelBug ...
And for gfx1103:
def FeatureISAVersion11_0_3 : FeatureSet<
!listconcat(FeatureISAVersion11_0_Common.Features,
[])>;
The mapping to gfx... names then happens in
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AMDGPU/GCNProcessors.td
such as:
def : ProcessorModel<"gfx1103", GFX11SpeedModel,
FeatureISAVersion11_0_3.Features
>;
Or for the generic one, i.e.:
// [gfx1100, gfx1101, gfx1102, gfx1103, gfx1150, gfx1151]
def : ProcessorModel<"gfx11-generic", GFX11SpeedModel,
FeatureISAVersion11_Generic.Features
LLVM also has some generic flags like the following in
https://github.com/llvm/llvm-project/blob/main/llvm/lib/TargetParser/TargetParser.cpp
{{"gfx1013"}, {"gfx1013"}, GK_GFX1013,
FEATURE_FAST_FMA_F32|FEATURE_FAST_DENORMAL_F32|FEATURE_WAVE32|FEATURE_XNACK|FEATURE_WGP},
I hope that this will give some inspiration – but I assume that at least
the initial implementation will be much shorter.
Tobias
