[llvm] r270449 - llvm-dwp: Add an abstraction for the DWP string pool

[Rafael Espíndola via llvm-commits]

Nah, it is fine. Just surprised that computing strlen once didn't make
it worth it.

Thanks,
Rafael

On 24 May 2016 at 11:39, David Blaikie <dblaikie at gmail.com> wrote:
>
>
> On Tue, May 24, 2016 at 4:54 AM, Rafael Espíndola
> <rafael.espindola at gmail.com> wrote:
>>
>> On 23 May 2016 at 12:32, David Blaikie via llvm-commits
>> <llvm-commits at lists.llvm.org> wrote:
>> > Author: dblaikie
>> > Date: Mon May 23 11:32:11 2016
>> > New Revision: 270449
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=270449&view=rev
>> > Log:
>> > llvm-dwp: Add an abstraction for the DWP string pool
>> >
>> > Also reference strings in the memory mapped file, reduces memory usage
>> > on a large test case by 18.5%.
>> >
>> > Added:
>> >     llvm/trunk/tools/llvm-dwp/DWPStringPool.h
>> > Modified:
>> >     llvm/trunk/tools/llvm-dwp/DWPError.h
>> >     llvm/trunk/tools/llvm-dwp/llvm-dwp.cpp
>> >
>> > Modified: llvm/trunk/tools/llvm-dwp/DWPError.h
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-dwp/DWPError.h?rev=270449&r1=270448&r2=270449&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/tools/llvm-dwp/DWPError.h (original)
>> > +++ llvm/trunk/tools/llvm-dwp/DWPError.h Mon May 23 11:32:11 2016
>> > @@ -1,6 +1,10 @@
>> > +#ifndef TOOLS_LLVM_DWP_DWPERROR
>> > +#define TOOLS_LLVM_DWP_DWPERROR
>> > +
>> >  #include "llvm/Support/Error.h"
>> >  #include "llvm/Support/ErrorHandling.h"
>> >  #include <string>
>> > +
>> >  namespace llvm {
>> >  class DWPError : public ErrorInfo<DWPError> {
>> >  public:
>> > @@ -15,3 +19,5 @@ private:
>> >    std::string Info;
>> >  };
>> >  }
>> > +
>> > +#endif
>> >
>> > Added: llvm/trunk/tools/llvm-dwp/DWPStringPool.h
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/tools/llvm-dwp/DWPStringPool.h?rev=270449&view=auto
>> >
>> > ==============================================================================
>> > --- llvm/trunk/tools/llvm-dwp/DWPStringPool.h (added)
>> > +++ llvm/trunk/tools/llvm-dwp/DWPStringPool.h Mon May 23 11:32:11 2016
>> > @@ -0,0 +1,54 @@
>> > +#ifndef TOOLS_LLVM_DWP_DWPSTRINGPOOL
>> > +#define TOOLS_LLVM_DWP_DWPSTRINGPOOL
>> > +
>> > +#include "llvm/ADT/DenseMap.h"
>> > +#include "llvm/MC/MCSection.h"
>> > +#include "llvm/MC/MCStreamer.h"
>> > +#include <cassert>
>> > +
>> > +class DWPStringPool {
>> > +
>> > +  struct CStrDenseMapInfo {
>> > +    static inline const char *getEmptyKey() {
>> > +      return reinterpret_cast<const char
>> > *>(~static_cast<uintptr_t>(0));
>> > +    }
>> > +    static inline const char *getTombstoneKey() {
>> > +      return reinterpret_cast<const char
>> > *>(~static_cast<uintptr_t>(1));
>> > +    }
>> > +    static unsigned getHashValue(const char *Val) {
>> > +      assert(Val != getEmptyKey() && "Cannot hash the empty key!");
>> > +      assert(Val != getTombstoneKey() && "Cannot hash the tombstone
>> > key!");
>> > +      return (unsigned)hash_value(StringRef(Val));
>> > +    }
>> > +    static bool isEqual(const char *LHS, const char *RHS) {
>> > +      if (RHS == getEmptyKey())
>> > +        return LHS == getEmptyKey();
>> > +      if (RHS == getTombstoneKey())
>> > +        return LHS == getTombstoneKey();
>> > +      return strcmp(LHS, RHS) == 0;
>> > +    }
>> > +  };
>> > +
>> > +  MCStreamer &Out;
>> > +  MCSection *Sec;
>> > +  DenseMap<const char *, uint32_t, CStrDenseMapInfo> Pool;
>> > +  uint32_t Offset = 0;
>>
>> Can't you use a DenseMap of StringRef?
>
>
> StringRef has a pointer and length - storing only a pointer is noticeably
> smaller due to there being quite so many of these. I can double back & check
> the numbers if you're curious.
>
> - Dave
>
>>
>>
>> Cheers,
>> Rafael
>
>