[llvm] 952c274 - [RDA] Use TinyPtrVector to store reaching defs (NFCI)

[Mikael Holmén via llvm-commits]

On Thu, 2020-04-09 at 10:55 +0200, Nikita Popov wrote:
> On Thu, Apr 9, 2020 at 7:53 AM Mikael Holmén <
> mikael.holmen at ericsson.com> wrote:
> > Hi,
> > 
> > In our downstream bots running with sanitizers we see lots of
> > complaints like
> > 
> > ../include/llvm/CodeGen/ReachingDefAnalysis.h:47:43: runtime error:
> > left shift of negative value -1
> > 
> > I haven't verified that they really start occuring with this patch,
> > but
> > the left shift it complains on was at least added here.
> > 
> > I think the same can be seen here:
> > http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast
> > 
> > /Mikael
> 
> Thanks for the pointer! This should be fixed with 
> https://github.com/llvm/llvm-project/commit/8f66f25f52f9b4089d216a33283acdb87ea3c250
> .

Great!

Thanks,
Mikael

> 
> Regards,
> Nikita
> 
> > On Wed, 2020-04-08 at 08:52 -0700, Nikita Popov via llvm-commits
> > wrote:
> > > Author: Nikita Popov
> > > Date: 2020-04-08T17:46:24+02:00
> > > New Revision: 952c2741599ed492cedd37da895d7e81bc175ab9
> > > 
> > > URL: 
> > > 
> > https://github.com/llvm/llvm-project/commit/952c2741599ed492cedd37da895d7e81bc175ab9
> > > DIFF: 
> > > 
> > https://github.com/llvm/llvm-project/commit/952c2741599ed492cedd37da895d7e81bc175ab9.diff
> > > 
> > > LOG: [RDA] Use TinyPtrVector to store reaching defs (NFCI)
> > > 
> > > RDA currently uses SmallVector<int, 1> to store reaching
> > definitions.
> > > A SmallVector<int, 1> is 24 bytes large, and X86 currently has
> > > 164 register units, which means we need 3936 bytes per block.
> > > If you have a large function with 1000 blocks, that's already
> > 4MB.
> > > 
> > > A large fraction of these reg units will not have any reaching
> > defs
> > > (say, those corresponding to zmm registers), and many will have
> > just
> > > one. A TinyPtrVector serves this use-case much better, as it only
> > > needs 8 bytes per register if it has 0 or 1 reaching defs.
> > > 
> > > As the name implies, TinyPtrVector is designed to work with
> > pointers,
> > > so we need to add some boilerplate to treat our reaching def
> > integers
> > > as pointers, using an appropriate encoding. We need to keep the
> > low
> > > bit free for tagging, and make sure at least one bit is set to
> > > distinguish the null pointer.
> > > 
> > > Differential Revision: https://reviews.llvm.org/D77513
> > > 
> > > Added: 
> > >     
> > > 
> > > Modified: 
> > >     llvm/include/llvm/CodeGen/ReachingDefAnalysis.h
> > > 
> > > Removed: 
> > >     
> > > 
> > > 
> > >
> > ###################################################################
> > ##
> > > ###########
> > > diff  --git a/llvm/include/llvm/CodeGen/ReachingDefAnalysis.h
> > > b/llvm/include/llvm/CodeGen/ReachingDefAnalysis.h
> > > index 608f0dff4ccb..8def1a6d39fc 100644
> > > --- a/llvm/include/llvm/CodeGen/ReachingDefAnalysis.h
> > > +++ b/llvm/include/llvm/CodeGen/ReachingDefAnalysis.h
> > > @@ -23,6 +23,7 @@
> > >  
> > >  #include "llvm/ADT/DenseMap.h"
> > >  #include "llvm/ADT/SmallVector.h"
> > > +#include "llvm/ADT/TinyPtrVector.h"
> > >  #include "llvm/CodeGen/LoopTraversal.h"
> > >  #include "llvm/CodeGen/MachineFunctionPass.h"
> > >  #include "llvm/InitializePasses.h"
> > > @@ -32,6 +33,37 @@ namespace llvm {
> > >  class MachineBasicBlock;
> > >  class MachineInstr;
> > >  
> > > +/// Thin wrapper around "int" used to store reaching
> > definitions,
> > > +/// using an encoding that makes it compatible with
> > TinyPtrVector.
> > > +/// The 0th LSB is forced zero (and will be used for pointer
> > union
> > > tagging),
> > > +/// The 1st LSB is forced one (to make sure the value is non-
> > zero).
> > > +class ReachingDef {
> > > +  uintptr_t Encoded;
> > > +  friend struct PointerLikeTypeTraits<ReachingDef>;
> > > +  explicit ReachingDef(uintptr_t Encoded) : Encoded(Encoded) {}
> > > +
> > > +public:
> > > +  ReachingDef(int Instr) : Encoded((Instr << 2) | 2) {}
> > > +  operator int() const { return ((int) Encoded) >> 2; }
> > > +};
> > > +
> > > +template<>
> > > +struct PointerLikeTypeTraits<ReachingDef> {
> > > +  static constexpr int NumLowBitsAvailable = 1;
> > > +
> > > +  static inline void *getAsVoidPointer(const ReachingDef &RD) {
> > > +    return reinterpret_cast<void *>(RD.Encoded);
> > > +  }
> > > +
> > > +  static inline ReachingDef getFromVoidPointer(void *P) {
> > > +    return ReachingDef(reinterpret_cast<uintptr_t>(P));
> > > +  }
> > > +
> > > +  static inline ReachingDef getFromVoidPointer(const void *P) {
> > > +    return ReachingDef(reinterpret_cast<uintptr_t>(P));
> > > +  }
> > > +};
> > > +
> > >  /// This class provides the reaching def analysis.
> > >  class ReachingDefAnalysis : public MachineFunctionPass {
> > >  private:
> > > @@ -61,7 +93,7 @@ class ReachingDefAnalysis : public
> > > MachineFunctionPass {
> > >    DenseMap<MachineInstr *, int> InstIds;
> > >  
> > >    /// All reaching defs of a given RegUnit for a given MBB.
> > > -  using MBBRegUnitDefs = SmallVector<int, 1>;
> > > +  using MBBRegUnitDefs = TinyPtrVector<ReachingDef>;
> > >    /// All reaching defs of all reg units for a given MBB
> > >    using MBBDefsInfo = std::vector<MBBRegUnitDefs>;
> > >    /// All reaching defs of all reg units for a all MBBs
> > > 
> > > 
> > >         
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