[PATCH] D38174: [TableGen] Return StringRef from ValueTypeByHwMode::getMVTName

[Krzysztof Parzyszek via llvm-commits]

The types are printed as comments in <Target>GenDAGISel.inc.

Also, it's very useful for debugging.

Replacing getAsString with writeToStream is fine. On that note, having 
an operator<< that can be invoked in a sequence with other <<'s would be 
great (it could be a wrapper around writeToStream).

-Krzysztof

On 9/22/2017 7:29 AM, Zachary Turner wrote:
> Who calls getAsString? I just noticed it's using a std::stringstream 
> again, which has terrible performance. One of the biggest improvements i 
> made originally was converting stringstream operations to llvm streams.
> 
> Is it possible to change this function to not return a std::string but 
> to instead accept a llvm::raw_ostream&?
> On Fri, Sep 22, 2017 at 5:22 AM Simon Pilgrim via Phabricator 
> <reviews at reviews.llvm.org <mailto:reviews at reviews.llvm.org>> wrote:
> 
>     RKSimon created this revision.
> 
>     Avoid unnecessary std::string creations during
>     TypeSetByHwMode::writeToStream.
> 
>     Found during investigations into PR28222
> 
> 
>     Repository:
>        rL LLVM
> 
>     https://reviews.llvm.org/D38174
> 
>     Files:
>        utils/TableGen/InfoByHwMode.cpp
>        utils/TableGen/InfoByHwMode.h
> 
> 
>     Index: utils/TableGen/InfoByHwMode.h
>     ===================================================================
>     --- utils/TableGen/InfoByHwMode.h
>     +++ utils/TableGen/InfoByHwMode.h
>     @@ -129,7 +129,7 @@
>         MVT getType(unsigned Mode) const { return get(Mode); }
>         MVT &getOrCreateTypeForMode(unsigned Mode, MVT Type);
> 
>     -  static std::string getMVTName(MVT T);
>     +  static StringRef getMVTName(MVT T);
>         std::string getAsString() const;
>         void dump() const;
>       };
>     Index: utils/TableGen/InfoByHwMode.cpp
>     ===================================================================
>     --- utils/TableGen/InfoByHwMode.cpp
>     +++ utils/TableGen/InfoByHwMode.cpp
>     @@ -70,10 +70,9 @@
>         return Map.insert(std::make_pair(Mode, Type)).first->second;
>       }
> 
>     -std::string ValueTypeByHwMode::getMVTName(MVT T) {
>     -  std::string N = llvm::getEnumName(T.SimpleTy);
>     -  if (N.substr(0,5) == "MVT::")
>     -    N = N.substr(5);
>     +StringRef ValueTypeByHwMode::getMVTName(MVT T) {
>     +  StringRef N = llvm::getEnumName(T.SimpleTy);
>     +  N.consume_front("MVT::");
>         return N;
>       }
> 
>     @@ -91,7 +90,7 @@
>         for (unsigned i = 0, e = Pairs.size(); i != e; ++i) {
>           const PairType *P = Pairs[i];
>           str << '(' << getModeName(P->first)
>     -        << ':' << getMVTName(P->second) << ')';
>     +        << ':' << getMVTName(P->second).str() << ')';
>           if (i != e-1)
>             str << ',';
>         }
> 
> 

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