[llvm] [llvm-debuginfo-analyzer][DOC] Convert 'README.txt' to markdown. (PR #86394)

Mon Mar 25 03:58:18 PDT 2024

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+# `llvm-debuginfo-analyzer`
+
+These are the notes collected during the development, review and test.
+They describe limitations, known issues and future work.
+
+### Remove the use of macros in ``LVReader.h`` that describe the ``bumpallocators``.
+**[D137933](https://reviews.llvm.org/D137933#inline-1389904)**
+
+Use a standard (or LLVM) ``map`` with ``typeinfo`` (would need a specialization
+to expose equality and hasher) for the allocators and the creation
+functions could be a function template.
+
+### Use a ``lit test`` instead of a ``unit test`` for the ``logical readers``.
+**[D125783](https://reviews.llvm.org/D125783#inline-1324376)**
+
+As the ``DebugInfoLogicalView`` library is sufficiently exposed via the
+``llvm-debuginfo-analyzer`` tool, follow the LLVM general approach and
+use ``LIT`` tests to validate the ``logical readers``.
+
+Convert the ``unitests``:
+```
+llvm-project/llvm/unittests/DebugInfo/LogicalView/CodeViewReaderTest.cpp
+llvm-project/llvm/unittests/DebugInfo/LogicalView/DWARFReaderTest.cpp
+```
+into ``LIT tests``:
+```
+llvm-project/llvm/test/DebugInfo/LogicalView/CodeViewReader.test
+llvm-project/llvm/test/DebugInfo/LogicalView/DWARFReader.test
+```
+
+### Eliminate calls to ``getInputFileDirectory()`` in the unit tests.
+**[D125783](https://reviews.llvm.org/D125783#inline-1324359)**
+
+Rewrite the unittests ``ReaderTest`` and ``CodeViewReaderTest`` to eliminate
+the call:
+```
+  getInputFileDirectory()
+```
+as use of that call is discouraged.
+
+### Fix mismatch between ``%d/%x`` format strings and ``uint64_t`` type.
+**[D137400](https://reviews.llvm.org/D137400) / [58758](https://github.com/llvm/llvm-project/issues/58758)**
+
+Incorrect printing of ``uint64_t`` on ``32-bit`` platforms.
+Add the ``PRIx64`` specifier to the printing code (``format()``).
+
+### Remove ``LVScope::Children`` container.
+**[D137933](https://reviews.llvm.org/D137933#inline-1373902)**
+
+Use a ``chaining iterator`` over the other containers rather than keep a
+separate container ``Children`` that mirrors their contents.
+
+### Use ``TableGen`` for command line options.
+**[D125777](https://reviews.llvm.org/D125777#inline-1291801)**
+
+The current trend is to use ``TableGen`` for command-line options in tools.
+Change command line options to use ``tablegen`` as many other LLVM tools.
+
+### ``LVDoubleMap`` to return ``optional<ValueType>`` instead of ``null pointer``.
+**[D125783](https://reviews.llvm.org/D125783#inline-1294164)**
+
+The more idiomatic LLVM way to handle this would be to have ``find``
+return ``Optional<ValueType>``.
+
+### Pass references instead of pointers (``Comparison functions``).
+**[D125782](https://reviews.llvm.org/D125782#inline-1293920)**
+
+In the ``comparison functions``, pass references instead of pointers (when
+pointers cannot be null).
+
+### Use ``StringMap`` where possible.
+**[D125783](https://reviews.llvm.org/D125783#inline-1294211)**
+
+LLVM has a ``StringMap`` class that is advertised as more efficient than
+``std::map<std::string, ValueType>``. Mainly it does fewer allocations
+because the key is not a ``std::string``.
+
+Replace the use of ``std::map<std::string, ValueType>`` with ``StringMap``.
+One specific case is the ``LVSymbolNames`` definitions.
+
+### Calculate unique offset for ``CodeView`` elements.
+In order to have the same logical functionality as the ``DWARF`` reader, such
+as:
+
+* find scopes contribution to debug info
+* sort by its physical location
+
+The logical elements must have an unique offset (similar like the ``DWARF
+DIE offset``).
+
+### Move ``initializeFileAndStringTables`` to the ``CodeView`` Library.
+There is some code in the ``CodeView`` reader that was extracted/adapted
+from ``tools/llvm-readobj/COFFDumper.cpp`` that can be moved to the ``CodeView``
+library.
+
+We had a similar case with code shared with ``llvm-pdbutil`` that was moved
+to the ``PDB`` library: **[D122226](https://reviews.llvm.org/D122226)**
+
+### Move ``getSymbolKindName`` and ``formatRegisterId`` to the ``CodeView`` Library.
+There is some code in the ``CodeView`` reader that was extracted/adapted
+from ``lib/DebugInfo/CodeView/SymbolDumper.cpp`` that can be used.
+
+### Use of ``std::unordered_set`` instead of ``std::set``.
+**[D125784](https://reviews.llvm.org/D125784#inline-1221421)**
+
+Replace the ``std::set`` usage for ``DeducedScopes``, ``UnresolvedScopes`` and
+``IdentifiedNamespaces`` with ``std::unordered_set`` and get the benefit
+of the O(1) while inserting/searching, as the order is not important.
+
+### Optimize ``LVNamespaceDeduction::find`` funtion.
+**[D125784](https://reviews.llvm.org/D125784#inline-1296195)**
+
+Optimize the ``find`` method to use the proposed code:
+
+```
+  LVStringRefs::iterator Iter = std::find_if(Components.begin(), Components.end(),
+    [](StringRef Name) {
+        return IdentifiedNamespaces.find(Name) == IdentifiedNamespaces.end();
+    });
+  LVStringRefs::size_type FirstNonNamespace = std::distance(Components.begin(), Iter);
+```
+
+### Move all the printing support to a common module.
+Factor out printing functionality from the logical elements into a
+common module.
+
+### Refactor ``LVBinaryReader::processLines``.
+**[D125783](https://reviews.llvm.org/D125783#inline-1246155) /
+[D137156](https://reviews.llvm.org/D137156)**
+
+During the traversal of the debug information sections, we created the
+logical lines representing the ``disassembled instructions`` from the ``text
+section`` and the logical lines representing the ``line records`` from the
+``debug line`` section. Using the ranges associated with the logical scopes,
+we will allocate those logical lines to their logical scopes.
+
+Consider the case when any of those lines become orphans, causing
+incorrect scope parent for disassembly or line records.
+
+### Add support for ``-ffunction-sections``.
+**[D125783](https://reviews.llvm.org/D125783#inline-1295012)**
+
+Only linked executables are handled. It does not support relocatable
+files compiled with ``-ffunction-sections``.
+
+### Add support for DWARF v5 .debug_names section / CodeView public symbols stream.
+**[D125783](https://reviews.llvm.org/D125783#inline-1294142)**
+
+The ``DWARF`` and ``CodeView`` readers use the public names information to create
+the instructions (``LVLineAssembler``). Instead of relying on ``DWARF`` section
+names (``.debug_pubnames``, ``.debug_names``) and ``CodeView`` ``public symbol`` stream
----------------
jryans wrote:

```suggestion
names (``.debug_pubnames``, ``.debug_names``) and ``CodeView`` public symbol stream
```

https://github.com/llvm/llvm-project/pull/86394
