"[RemoteInspection] Read ContextDescriptor from symbol if available" and "[RemoteInspection] Factor out buildContextDescriptorManglingForSymbol" #85907
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If the MemoryReader can provide a symbol for the context descriptor, use that instead of building the mangle tree from metadata. This shouldn't hurt other clients, and would have a few benefits for LLDB: - Small but numerous memory reads can be expensive for LLDB, building the mangle tree from a string should be much faster. - For types with private discriminators, this allows LLDB to provide the same private discriminator that's in DWARF and in the swiftmodule (as opposed to using the memory address where the context descriptor lives at). This means that these private types would have the same mangled name in every run. LLDB persistently caches field descriptors by name, but since private discriminators aren't guaranteed to have the same mangled name over multiple runs, LLDB would often need to invalidate its entire cache and rebuild it. Using the stable UUID would solve that issue. rdar://165950673 (cherry picked from commit e3c67c9)
A previous commit introduced the usage of buildContextManglingForSymbol in buildContextDescriptorMangling, which was not quite correct, since type nodes needed extra handling, which was done in the other version of buildContextDescriptorMangling. This patch factors out the handling of building context descriptors mangling from symbols, and updates both call sites to use the new function instead. rdar://165950673 (cherry picked from commit ab507be)
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• Explanation: If the MemoryReader can provide a symbol for the context descriptor, use that instead of building the mangle tree from metadata. This shouldn't hurt other clients, and would have a few benefits for LLDB:
Small but numerous memory reads can be expensive for LLDB, building the mangle tree from a string should be much faster.
For types with private discriminators, this allows LLDB to provide the same private discriminator that's in DWARF and in the swiftmodule (as opposed to using the memory address where the context descriptor lives at). This means that these private types would have the same mangled name in every run. LLDB persistently caches field descriptors by name, but since private discriminators aren't guaranteed to have the same mangled name over multiple runs, LLDB would often need to invalidate its entire cache and rebuild it. Using the stable UUID would solve that issue.
• Scope: This affects RemoteInspection clients that override resolvePointerAsSymbol, which effectively is just LLDB.
• Risk: Low, this only affects LLDB, and the existing code validates that the symbol LLDB provides is valid.
• Problem: rdar://165950673
• Original PR: [RemoteInspection] Read ContextDescriptor from symbol if available #85878 and [RemoteInspection] Factor out buildContextDescriptorManglingForSymbol #85911