[lld] r222455 - [mach-o] use reference with "auto" to prevent copies

[David Blaikie]

On Thu, Nov 20, 2014 at 1:19 PM, Nick Kledzik <kledzik at apple.com> wrote:

> Author: kledzik
> Date: Thu Nov 20 15:19:58 2014
> New Revision: 222455
>
> URL: http://llvm.org/viewvc/llvm-project?rev=222455&view=rev
> Log:
> [mach-o] use reference with "auto" to prevent copies
>
> Patch by Jean-Daniel Dupas
>
> Modified:
>     lld/trunk/lib/ReaderWriter/MachO/File.h
>
> Modified: lld/trunk/lib/ReaderWriter/MachO/File.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/MachO/File.h?rev=222455&r1=222454&r2=222455&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/MachO/File.h (original)
> +++ lld/trunk/lib/ReaderWriter/MachO/File.h Thu Nov 20 15:19:58 2014
> @@ -118,13 +118,13 @@ public:
>    MachODefinedAtom *findAtomCoveringAddress(const Section &section,
>                                              uint64_t offsetInSect,
>                                              uint32_t
> *foundOffsetAtom=nullptr) {
> -    auto pos = _sectionAtoms.find(&section);
> +    const auto& pos = _sectionAtoms.find(&section);
>

This one's a bit weird - 'find' (for any standard-like container, at least)
returns an iterator by value. While taking a reference to that is valid
(reference lifetime extension & all that) it's a bit surprising &
unnecessary (has basically the same semantics as the non-reference code).


>      if (pos == _sectionAtoms.end())
>        return nullptr;
> -    auto vec = pos->second;
> +    const auto& vec = pos->second;
>      assert(offsetInSect < section.content.size());
>      // Vector of atoms for section are already sorted, so do binary
> search.
> -    auto atomPos = std::lower_bound(vec.begin(), vec.end(), offsetInSect,
> +    const auto& atomPos = std::lower_bound(vec.begin(), vec.end(),
> offsetInSect,
>

Same here, lower_bound just returns an iterator by value, this doesn't look
like it's avoiding any copies.


>          [offsetInSect](const SectionOffsetAndAtom &ao,
>                         uint64_t targetAddr) -> bool {
>            // Each atom has a start offset of its slice of the
>
>
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