[lldb] Add DisassemblerLLVMC::IsBarrier API

[felipepiovezan]

This will allow the instruction emulation unwinder to reason about
instructions that prevent the subsequent instruction from executing.

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:bb5df4aa

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Felipe de Azevedo Piovezan (felipepiovezan)

Changes

This will allow the instruction emulation unwinder to reason about
instructions that prevent the subsequent instruction from executing.

commit-id:bb5df4aa

---

Full diff: https://github.com/llvm/llvm-project/pull/169632.diff

3 Files Affected:

• (modified) lldb/include/lldb/Core/Disassembler.h (+4)
• (modified) lldb/source/Core/Disassembler.cpp (+5)
• (modified) lldb/source/Plugins/Disassembler/LLVMC/DisassemblerLLVMC.cpp (+13)

diff --git a/lldb/include/lldb/Core/Disassembler.h b/lldb/include/lldb/Core/Disassembler.h
index 5de314109b0cc..ab0f4ac804a7c 100644
--- a/lldb/include/lldb/Core/Disassembler.h
+++ b/lldb/include/lldb/Core/Disassembler.h
@@ -167,6 +167,8 @@ class Instruction {
 
   virtual bool IsLoad() = 0;
 
+  virtual bool IsBarrier() = 0;
+
   virtual bool IsAuthenticated() = 0;
 
   bool CanSetBreakpoint();
@@ -367,6 +369,8 @@ class PseudoInstruction : public Instruction {
 
   bool IsLoad() override;
 
+  bool IsBarrier() override;
+
   bool IsAuthenticated() override;
 
   void CalculateMnemonicOperandsAndComment(
diff --git a/lldb/source/Core/Disassembler.cpp b/lldb/source/Core/Disassembler.cpp
index f2eb887986bfb..ed32caf361e0a 100644
--- a/lldb/source/Core/Disassembler.cpp
+++ b/lldb/source/Core/Disassembler.cpp
@@ -1341,6 +1341,11 @@ bool PseudoInstruction::DoesBranch() {
   return false;
 }
 
+bool PseudoInstruction::IsBarrier() {
+  // This is NOT a valid question for a pseudo instruction.
+  return false;
+}
+
 bool PseudoInstruction::HasDelaySlot() {
   // This is NOT a valid question for a pseudo instruction.
   return false;
diff --git a/lldb/source/Plugins/Disassembler/LLVMC/DisassemblerLLVMC.cpp b/lldb/source/Plugins/Disassembler/LLVMC/DisassemblerLLVMC.cpp
index 66d0a50985be7..e8bb706f7aab6 100644
--- a/lldb/source/Plugins/Disassembler/LLVMC/DisassemblerLLVMC.cpp
+++ b/lldb/source/Plugins/Disassembler/LLVMC/DisassemblerLLVMC.cpp
@@ -70,6 +70,7 @@ class DisassemblerLLVMC::MCDisasmInstance {
   bool HasDelaySlot(llvm::MCInst &mc_inst) const;
   bool IsCall(llvm::MCInst &mc_inst) const;
   bool IsLoad(llvm::MCInst &mc_inst) const;
+  bool IsBarrier(llvm::MCInst &mc_inst) const;
   bool IsAuthenticated(llvm::MCInst &mc_inst) const;
 
 private:
@@ -436,6 +437,11 @@ class InstructionLLVMC : public lldb_private::Instruction {
     return m_is_load;
   }
 
+  bool IsBarrier() override {
+    VisitInstruction();
+    return m_is_barrier;
+  }
+
   bool IsAuthenticated() override {
     VisitInstruction();
     return m_is_authenticated;
@@ -1195,6 +1201,7 @@ class InstructionLLVMC : public lldb_private::Instruction {
   bool m_is_call = false;
   bool m_is_load = false;
   bool m_is_authenticated = false;
+  bool m_is_barrier = false;
 
   void VisitInstruction() {
     if (m_has_visited_instruction)
@@ -1227,6 +1234,7 @@ class InstructionLLVMC : public lldb_private::Instruction {
     m_is_call = mc_disasm_ptr->IsCall(inst);
     m_is_load = mc_disasm_ptr->IsLoad(inst);
     m_is_authenticated = mc_disasm_ptr->IsAuthenticated(inst);
+    m_is_barrier = mc_disasm_ptr->IsBarrier(inst);
   }
 
 private:
@@ -1432,6 +1440,11 @@ bool DisassemblerLLVMC::MCDisasmInstance::IsLoad(llvm::MCInst &mc_inst) const {
   return m_instr_info_up->get(mc_inst.getOpcode()).mayLoad();
 }
 
+bool DisassemblerLLVMC::MCDisasmInstance::IsBarrier(
+    llvm::MCInst &mc_inst) const {
+  return m_instr_info_up->get(mc_inst.getOpcode()).isBarrier();
+}
+
 bool DisassemblerLLVMC::MCDisasmInstance::IsAuthenticated(
     llvm::MCInst &mc_inst) const {
   const auto &InstrDesc = m_instr_info_up->get(mc_inst.getOpcode());

[DavidSpickett]

LGTM

Feels a bit awkward to have this proxy class around the instruction but I'm sure someone had a good reason (tm) for it.