[PATCH] D102401: [AMDGPU] Allocate LDS globals in sorted order of their alignment and size.

[Jay Foad via Phabricator via llvm-commits]

foad added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/Utils/AMDGPULDSUtils.cpp:115
+  SmallVector<const GlobalVariable *, 8> StaticLDSGlobals =
+      collectStaticLDSGlobals(&M);
+
----------------
hsmhsm wrote:
> hsmhsm wrote:
> > foad wrote:
> > > hsmhsm wrote:
> > > > rampitec wrote:
> > > > > hsmhsm wrote:
> > > > > > rampitec wrote:
> > > > > > > Maybe just pass a filter lambda there?
> > > > > > I personally think that it will be over complicated - collectStaticLDSGlobals() is called by both findVariablesToLower() and getSortedUsedLDSGlobals().  Further filtering of LDS globals is required for findVariablesToLower(), but not for getSortedUsedLDSGlobals().
> > > > > I do not like the idea of allocating memory, then copying.
> > > > Then you mean to say, let's return vector, instead of passing it as reference arg? then we cannot use SmallVectorImpl<> as return type, so, we need to go back to returning SmallVector<> itself.
> > > To avoid allocating memory for a copy of the data, you could filter StaticLDSGlobals in-place with `erase(remove_if(StaticLDSGlobals.begin(), StaticLDSGlobals.end(), predicate), StaticLDSGlobals.end())`.
> > Probably, we land-up with code like below. We still need to copy to `LocalVars`, because findVariablesToLower() expect return std::vector. And, based on earlier reveiw comments, I have made changes to collectStaticLDSGlobals() to work with SmallVector. Additionally, look at the complexity of the code change in terms of understanding it. So, I thought it is not worth, since we still need to copy anyway.
> > 
> > ```
> >   StaticLDSGlobals.erase(
> >     std::remove_if(StaticLDSGlobals.begin(), StaticLDSGlobals.end(),
> >                  [&](const GlobalVariable *GV) {
> >                    GlobalVariable *GV2 = const_cast<GlobalVariable *>(GV);
> >                     if (std::none_of(GV2->user_begin(), GV2->user_end(), [&](User *U) {
> >                           return userRequiresLowering(UsedList, U);
> >                         })) {
> >                       return true;
> >                     }
> >                     return false;
> >                  }),
> >     StaticLDSGlobals.end());
> > 
> >   std::vector<llvm::GlobalVariable *> LocalVars(StaticLDSGlobals.begin(),
> >                                                 StaticLDSGlobals.end());
> > ```
> Additionally, there is also a added complexity of handling "constness" of "GlobalVariable *"
```
                  if (std::none_of(GV2->user_begin(), GV2->user_end(), [&](User *U) {
                        return userRequiresLowering(UsedList, U);
                      })) {
                    return true;
                  }
                  return false;
```
This should just `return std::none_of(...);`

> Additionally, there is also a added complexity of handling "constness" of "GlobalVariable *"

Then fix `userRequiresLowering` first? Something like: https://reviews.llvm.org/differential/diff/346095/


Repository:
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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102401/new/

https://reviews.llvm.org/D102401