[lldb] Handle backwards branches in UnwindAssemblyInstEmulation (#169633) This allows the unwinder to handle code with mid-function epilogues where the subsequent code is reachable through a backwards branch. Two changes are required to accomplish this: 1. Do not enqueue the subsequent instruction if the current instruction is a barrier(*). 2. When processing an instruction, stop ignoring branches with negative offsets. (*) As per the definition in LLVM's MC layer, a barrier is any instruction that "stops control flow from executing the instruction immediately following it". See `MCInstrDesc::isBarrier` in MCInstrDesc.h Part of a sequence of PRs: [lldb][NFCI] Rewrite UnwindAssemblyInstEmulation in terms of a CFG visit #169630 [lldb][NFC] Rename forward_branch_offset to branch_offset in UnwindAssemblyInstEmulation #169631 [lldb] Add DisassemblerLLVMC::IsBarrier API #169632 [lldb] Handle backwards branches in UnwindAssemblyInstEmulation #169633 commit-id:fd266c13
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