================
@@ -321,6 +326,10 @@ class SymbolFileDWARFDebugMap : public SymbolFileCommon {
std::vector<uint32_t> m_func_indexes; // Sorted by address
std::vector<uint32_t> m_glob_indexes;
std::map<std::pair<ConstString, llvm::sys::TimePoint<>>, OSOInfoSP>
m_oso_map;
+ // A map from CompilerType to the struct/class/union/enum DIE (might be a
+ // declaration or a definition) that is used to construct it.
+ llvm::DenseMap<lldb::opaque_compiler_type_t, DIERef>
+ m_forward_decl_compiler_type_to_die;
----------------
ZequanWu wrote:
TL;DR: This is because this change let `UniqueDWARFASTTypeMap` to cache created
Type from declaration DIE. Before this, it was only used for caching Type
created from definition DIE. And `UniqueDWARFASTTypeMap` is shared among all
`SymbolFileDWARF`s belongs to one `SymbolFileDWARFDebugMap`, so should
`m_forward_decl_compiler_type_to_die` which interacts with it.
Here's an example with debug map used:
The declaration DIE for `bar` is in foo.o and the definition DIE is in main.o.
`ParseStructureLikeDIE` was firstly asked to parse the declaration DIE.
Before, it will always find the definition DIE in main.o and insert the
CompilerType to definition DIE to `m_forward_decl_compiler_type_to_die` which
belongs to SymbolFileDWARF(main.o). When `TypeSystemClang::CompleteTagDecl`
wants to complete `bar`, it asks `SymbolFileDWARFDebugMap::CompleteType` to
complete, which iterates all its SymbolFileDWARF(main.o, foo.o) and check if
the any of them has the compiler type in their maps:
https://github.com/llvm/llvm-project/blob/9144553207052a868efc5a8ce61a0afbb0eaf236/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDebugMap.cpp#L808-L812.
If exists, then it assumes that symbol file should have the definition DIE and
able to complete it. Since `bar`'s compiler type exists in symbol
file(main.o)'s map which also has the definition DIE as value, the type
completion will success.
If I don't add the fix, we have [bar's compiler type -> bar's declaration DIE]
in foo.o's map. When searching for definition DIE, we found that in main.o.
Because we have already created its Type from declaration, the
`UniqueDWARFASTTypeMap` will find the entry. Then it updates the entry to
points to the definition DIE. It updates main.o's
`m_forward_decl_compiler_type_to_die` to pointing to the definition DIE, which
is **wrong**, since there's no such entry in main.o's map. It should update
foo.o's map. The result is that `SymbolFileDWARFDebugMap::CompleteType` find
bar's compiler type exists in foo.o and ask foo.o's symbol file to complete it,
but it only has declaration DIE.
The fix is to share one `m_forward_decl_compiler_type_to_die` among one
`SymbolFileDWARFDebugMap`. With this, when creating compiler type to
declaration DIE in the map or updating an entry to point to a definition DIE,
we are operating in the same map.
https://github.com/llvm/llvm-project/pull/92328
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