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(The profile format change is split into a standalone change into https://github.com/llvm/llvm-project/pull/81691) * For InstrFDO value profiling, implement instrumentation and lowering for virtual table address. * This is controlled by `-enable-vtable-value-profiling` and off by default. * When the option is on, raw profiles will carry serialized `VTableProfData` structs and compressed vtables as payloads. * Implement profile reader and writer support * Raw profile reader is used by `llvm-profdata` but not compiler. Raw profile reader will construct InstrProfSymtab with symbol names, and map profiled runtime address to vtable symbols. * Indexed profile reader is used by `llvm-profdata` and compiler. When initialized, the reader stores a pointer to the beginning of in-memory compressed vtable names and the length of string. When used in `llvm-profdata`, reader decompress the string to show symbols of a profiled site. When used in compiler, string decompression doesn't happen since IR is used to construct InstrProfSymtab. * Indexed profile writer collects the list of vtable names, and stores that to index profiles. * Text profile reader and writer support are added but mostly follow the implementation for indirect-call value type. * `llvm-profdata show -show-vtables <args> <profile>` is implemented. rfc in https://discourse.llvm.org/t/rfc-dynamic-type-profiling-and-optimizations-in-llvm/74600#pick-instrumentation-points-and-instrument-runtime-types-7