[PATCH] D26567: Improve DWARF parsing speed by improving DWARFAbbreviationDeclaration

[Greg Clayton via llvm-commits]

clayborg created this revision.
clayborg added reviewers: dblaikie, probinson, aprantl, llvm-commits.

This patch gets a DWARF parsing speed improvement by having DWARFAbbreviationDeclaration instances know if they have a fixed byte size. If an abbreviation has a fixed byte size that can be calculated given a DWARFUnit, then parsing a DIE becomes two steps: parse ULEB128 abbrev code, and then add constant size to the offset.

This patch also adds a fixed byte size to each DWARFAbbreviationDeclaration::AttributeSpec so that attributes can quickly skip their values if needed without the need to lookup the fixed for size.

Notable improvements:

- DWARFAbbreviationDeclaration::findAttributeIndex() now returns an Optional<uint32_t> instead of a uint32_t and we no longer have to look for the magic -1U return value

  Optional<uint32_t> DWARFAbbreviationDeclaration::findAttributeIndex(dwarf::Attribute attr) const;

- DWARFAbbreviationDeclaration now has a getAttributeValue() function that extracts an attribute value given a DIE offset that takes advantage of the DWARFAbbreviationDeclaration::AttributeSpec::ByteSize

  bool DWARFAbbreviationDeclaration::getAttributeValue(const uint32_t DIEOffset, const dwarf::Attribute Attr, const DWARFUnit &U, DWARFFormValue &FormValue) const;

- A DWARFAbbreviationDeclaration instance can return a fixed byte size for itself so DWARF parsing is faster:

  Optional<size_t> DWARFAbbreviationDeclaration::getFixedAttributesByteSize(const DWARFUnit &U) const;

- Any functions that used to take a "const DWARFUnit *U" that would crash if U was NULL now take a "const DWARFUnit &U" and are only called with a valid DWARFUnit


https://reviews.llvm.org/D26567

Files:
  include/llvm/DebugInfo/DWARF/DWARFAbbreviationDeclaration.h
  include/llvm/DebugInfo/DWARF/DWARFDebugInfoEntry.h
  include/llvm/DebugInfo/DWARF/DWARFFormValue.h
  lib/DebugInfo/DWARF/DWARFAbbreviationDeclaration.cpp
  lib/DebugInfo/DWARF/DWARFDebugInfoEntry.cpp
  lib/DebugInfo/DWARF/DWARFUnit.cpp
  tools/dsymutil/DwarfLinker.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D26567.77678.patch
Type: text/x-patch
Size: 18112 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20161111/0cf51b3c/attachment.bin>