[PATCH] D92115: AMDGPU - Add diagnostic for compiling modules with AMD HSA OS type and GFX 6 arch

[Stanislav Mekhanoshin via Phabricator via cfe-commits]

rampitec added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp:62-72
+static AMDGPUSubtarget::Generation initializeGen(const Triple &TT,
+                                                 StringRef GPU) {
+  if (GPU.contains("generic")) {
+    return TT.getOS() == Triple::AMDHSA
+               ? AMDGPUSubtarget::Generation::SEA_ISLANDS
+               : AMDGPUSubtarget::Generation::SOUTHERN_ISLANDS;
+  } else {
----------------
t-tye wrote:
> I am not clear what this function is doing. It seems to be returning a generation unrelated to to the actual target generation to satisfy the one place it is called. If the target is not SEA_ISLANDS it seems incorrect to be returning SEA_ISLANDS. If this function is doing something special for the one place it is called perhaps it should be expanded there?
It is probably better just print an error if amdhsa is requested but no compatible -mcpu specified (e.g. when we have generic/tahiti etc).


================
Comment at: llvm/lib/Target/AMDGPU/AMDGPUSubtarget.cpp:134
+  if (isAmdHsaOS() && getGeneration() == AMDGPUSubtarget::SOUTHERN_ISLANDS) {
+    report_fatal_error("GFX6 (SI) ASICs does not support AMD HSA OS type \n",
+                       false);
----------------
pvellien wrote:
> t-tye wrote:
> > pvellien wrote:
> > > t-tye wrote:
> > > > rampitec wrote:
> > > > > "do not support". I would also drop "(SI)" from the message. Maybe even better just "GFX6 does not support AMD HSA".
> > > > Make the message include the full target triple text so the user understands how to resolve the issue. For example:
> > > > 
> > > >   The target triple %s is not supported: the processor %s does not support the amdhsa OS
> > > > 
> > > > Do the r600 targets also produce a similar error message?
> > > > 
> > > > Is this really the right test? My understanding is that the issue is not that gfx60x does not support the amdhsa OS, but that it does not use the FLAT address space.
> > > > 
> > > > My understanding is that the current problem is that FLAT instructions are being used for the GLOBAL address space accesses. The use of FLAT instructions for the global address space was introduced after gfx60x was initially being supported on amdhsa. Originally BUFFER instructions that use an SRD that has a 0 base and are marked as addr64 where used for GLOBAL address space accesses. This was changed to use FLAT instructions due to later targets dropping the SRD addr64 support. I suspect it is that change that broke gfx60x as there were no tests to catch it.
> > > > 
> > > > So the real fix seems to find that change and make the code still use use BUFFER instructions for gfxx60x and FLAT instructions for gfx70x+. The tests can then be updated to test gfx60x for amdhsa but to omit the FLAT address space tests. The error would then indicate that the gfx60x does not support the FLAT address space (and that is not conditional on the OS). The documentation in AMDGPUUsage can state that gfx60x does not support the FLAT address space in the Address Space section. The Processor table can add a column for processor characteristics and mention that the gfx60x targets do not support the FLAT address space.
> > > Previously in the internal review process it mentioned that gfx60x does not support HSA and agreed to add a diagnostic to report that GFX6 do not support HSA OS type, @rampitec mentioned that SI ASICs cannot support HSA because we can't able to map memory on SI as HSA requires so the user will just have weird runtime failures. But based on your comment it seems like we have to use MUBUF instructions for -mtriple=amdgcn-amd-amdhsa -mcpu=gfx60x combination and use FLAT instructions for -mtriple=amdgcn-amd-amdhsa -mcpu=gfx70x+. Is my understanding correct? If the compiler emits the MUBUF instructions for global address space accesses, it is still required to produce the error msg? 
> > In the early days of implementing HSA I believe we were bringing up on gfx6. It could not support all HSA features, but it did function with the parts it could support. So I was suggesting we restore the code to support what it did originally. That would mean using MUBUF for the GLOBAL address space like it used to do (is that code still present?).
> > 
> > The compiler can then report errors for the features it cannot support, which in this case is it cannot support instruction selection of the GENERIC address space on gfx6.
> > 
> > If you could find the commit that switched to using FLAT instructions to access the GLOBAL address space that will likely provide the necessary information to decide the best thing to do for this issue.
> I code to select MUBUF instructions for Global address space is still present, In fact my first patch for this issue is to generate MUBUF instructions instead of reporting error. But it got rejected due to SI ASICs do not support HSA. 
> This is the patch [[ https://reviews.llvm.org/D15543 |  https://reviews.llvm.org/D15543 ]] which switched to using FLAT instructions for global. 
> So whether the new approach is to off FlatForGlobal flag for -mtriple=amdgcn-amd-amdhsa -mcpu=gfx60x combination and generate MUBUF instructions instead. It would be very much to know what is the expectation :)  whether we wait for @rampitec for a comment
> Btw, thanks a lot for your feedback. 
We can try to use MUBUF for global, but we certainly cannot support HSA and/or generic pointers on SI.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D92115/new/

https://reviews.llvm.org/D92115