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

[Rafael Avila de Espindola via llvm-commits]

Michael Spencer via Phabricator via llvm-commits
<llvm-commits at lists.llvm.org> writes:

> @@ -1110,6 +1111,14 @@
>  // If no layout was provided by linker script, we want to apply default
>  // sorting for special input sections. This also handles --symbol-ordering-file.
>  template <class ELFT> void Writer<ELFT>::sortInputSections() {
> +  // Use the rarely used option -call-graph-ordering-file to sort sections.
> +  if (!Config->CallGraphProfile.empty()) {
> +    DenseMap<const InputSectionBase *, int> Order =
> +        computeCallGraphProfileOrder();
> +    for (BaseCommand *Base : Script->SectionCommands)
> +      if (auto *Sec = dyn_cast<OutputSection>(Base))
> +        sortSection(Sec, Order);
> +  }

Instead of adding this if you can change buildSectionOrder:

static DenseMap<const InputSectionBase *, int> buildSectionOrder() {
  if (!Config->CallGraphProfile.empty())
    return computeCallGraphProfileOrder();
  ...


> +    InputSectionBase *FromSec = SymbolSection.lookup(Fields[0]);
> +    InputSectionBase *ToSec = SymbolSection.lookup(Fields[1]);
> +    if (FromSec && ToSec)
> +      Config->CallGraphProfile[std::make_pair(FromSec, ToSec)] = Count;

This should be "+=", no? If there are multiple calls from one section to
another I would expect us to use the total in the graph.


> +struct EdgeDenseMapInfo {
> +  static Edge getEmptyKey() {
> +    return {DenseMapInfo<SectionIndex>::getEmptyKey(),
> +            DenseMapInfo<SectionIndex>::getEmptyKey(), 0, 0};
> +  }

This doesn't build with clang:

/home/espindola/llvm/llvm/tools/lld/ELF/CallGraphSort.cpp:115:12: error:
no matching constructor for initialization of '(anonymous
namespace)::Edge'
    return {DenseMapInfo<SectionIndex>::getEmptyKey(),
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/espindola/llvm/llvm/tools/lld/ELF/CallGraphSort.cpp:104:8: note:
candidate constructor (the implicit copy constructor) not viable:
requires 1 argument, but 4 were provided
struct Edge {
       ^
/home/espindola/llvm/llvm/tools/lld/ELF/CallGraphSort.cpp:104:8: note:
candidate constructor (the implicit move constructor) not viable:
requires 1 argument, but 4 were provided
/home/espindola/llvm/llvm/tools/lld/ELF/CallGraphSort.cpp:104:8: note:
candidate constructor (the implicit default constructor) not viable:
requires 0 arguments, but 4 were provided


Cheers,
Rafael