[PATCH] D36351: [lld][ELF] Add profile guided section layout

[Rafael Avila de Espindola via llvm-commits]

> +static void readCallGraph(MemoryBufferRef MB) {
> +  // Build a map from symbol name to section
> +  DenseMap<StringRef, InputSectionBase *> SymbolSection;
> +  for (InputFile *File : ObjectFiles)
> +    for (Symbol *Sym : File->getSymbols())
> +      if (auto *D = dyn_cast<Defined>(Sym))
> +        if (auto *IS = dyn_cast_or_null<InputSectionBase>(D->Section))
> +          SymbolSection[D->getName()] = IS;
> +
> +  std::vector<StringRef> Lines = args::getLines(MB);
> +  for (StringRef L : Lines) {
> +    SmallVector<StringRef, 3> Fields;
> +    L.split(Fields, ' ');
> +    if (Fields.size() != 3)
> +      fatal("parse error");
> +    uint64_t Count;
> +    if (!to_integer(Fields[2], Count))
> +      fatal("parse error");
> +    InputSectionBase *FromSec = SymbolSection.lookup(Fields[0]);
> +    InputSectionBase *ToSec = SymbolSection.lookup(Fields[1]);
> +    if (FromSec && ToSec)
> +      Config->CallGraphProfile[std::make_pair(FromSec, ToSec)] += Count;

Should this be using FromSec->Repl, ToSec->Repl to handle ICF? If so
please update the code and add a new test (the one in the patch is
getting big).

> +  }
> +}

With --symbol-ordering-file we produce warnings if, for example, the
symbol is found to be absolute. The same issue applies here, no? Can you
refactor the code so that we print the same warnings for
--call-graph-ordering-file?

> +using ClusterIndex = std::ptrdiff_t;
> +using SectionIndex = std::ptrdiff_t;
> +using EdgeIndex = std::ptrdiff_t;

Does this means that we use 64 bit integers for indexes? Why?

> +// Used for calculating an comparing density.  Use soft-float for determinism.
> +struct Double : APFloat {

This used to be a problem with x87, but do we support a system today
where this is a problem?

Cheers,
Rafael