[lldb] Implement CLI support for reverse-continue

This introduces the options "-F/--forward" and
"-R/--reverse" to `process continue`.

These only work if you're running with a gdbserver
backend that supports reverse execution, such as
rr. For testing we rely on the fake reverse-
execution functionality in `lldbreverse.py`.

Author: rocallahan

lldb/source/Commands/CommandObjectProcess.cpp

@@ -468,7 +468,23 @@ class CommandObjectProcessContinue : public CommandObjectParsed {
       case 'b':
         m_run_to_bkpt_args.AppendArgument(option_arg);
         m_any_bkpts_specified = true;
-      break;
+        break;
+      case 'F':
+        if (m_base_direction == lldb::RunDirection::eRunReverse) {
+          error = Status::FromErrorString(
+                "cannot specify both 'forward' and 'reverse'");
+          break;
+        }
+        m_base_direction = lldb::RunDirection::eRunForward;
+        break;
+      case 'R':
+        if (m_base_direction == lldb::RunDirection::eRunForward) {
+          error = Status::FromErrorString(
+                "cannot specify both 'forward' and 'reverse'");
+          break;
+        }
+        m_base_direction = lldb::RunDirection::eRunReverse;
+        break;
       default:
         llvm_unreachable("Unimplemented option");
       }
@@ -479,6 +495,7 @@ class CommandObjectProcessContinue : public CommandObjectParsed {
       m_ignore = 0;
       m_run_to_bkpt_args.Clear();
       m_any_bkpts_specified = false;
+      m_base_direction = std::nullopt;
     }
 
     llvm::ArrayRef<OptionDefinition> GetDefinitions() override {
@@ -488,6 +505,7 @@ class CommandObjectProcessContinue : public CommandObjectParsed {
     uint32_t m_ignore = 0;
     Args m_run_to_bkpt_args;
     bool m_any_bkpts_specified = false;
+    std::optional<lldb::RunDirection> m_base_direction;
   };
 
   void DoExecute(Args &command, CommandReturnObject &result) override {
@@ -654,6 +672,10 @@ class CommandObjectProcessContinue : public CommandObjectParsed {
         }
       }
 
+      if (m_options.m_base_direction.has_value()) {
+        process->SetBaseDirection(*m_options.m_base_direction);
+      }
+
       const uint32_t iohandler_id = process->GetIOHandlerID();
 
       StreamString stream;

lldb/source/Commands/Options.td

@@ -744,6 +744,10 @@ let Command = "process continue" in {
     Arg<"BreakpointIDRange">, Desc<"Specify a breakpoint to continue to, temporarily "
     "ignoring other breakpoints.  Can be specified more than once.  "
     "The continue action will be done synchronously if this option is specified.">;
+  def thread_continue_forward : Option<"forward", "F">, Group<3>,
+    Desc<"Execute in forward direction">;
+  def thread_continue_reverse : Option<"reverse", "R">, Group<3>,
+    Desc<"Execute in forward direction">;
 }
 
 let Command = "process detach" in {