Allow disabling state tracking for faster startup.

lib/runtime-core/src/backend.rs

@@ -117,6 +117,7 @@ pub struct CompilerConfig {
     pub symbol_map: Option<HashMap<u32, String>>,
     pub memory_bound_check_mode: MemoryBoundCheckMode,
     pub enforce_stack_check: bool,
+    pub track_state: bool,
 }
 
 pub trait Compiler {

lib/singlepass-backend/src/codegen_x64.rs

@@ -317,6 +317,7 @@ pub struct CodegenError {
 struct CodegenConfig {
     memory_bound_check_mode: MemoryBoundCheckMode,
     enforce_stack_check: bool,
+    track_state: bool,
 }
 
 impl ModuleCodeGenerator<X64FunctionCode, X64ExecutionContext, CodegenError>
@@ -366,7 +367,8 @@ impl ModuleCodeGenerator<X64FunctionCode, X64ExecutionContext, CodegenError>
 
         begin_label_info.1 = Some(begin_offset);
         let begin_label = begin_label_info.0;
-        let machine = Machine::new();
+        let mut machine = Machine::new();
+        machine.track_state = self.config.as_ref().unwrap().track_state;
 
         dynasm!(
             assembler
@@ -532,6 +534,7 @@ impl ModuleCodeGenerator<X64FunctionCode, X64ExecutionContext, CodegenError>
         self.config = Some(Arc::new(CodegenConfig {
             memory_bound_check_mode: config.memory_bound_check_mode,
             enforce_stack_check: config.enforce_stack_check,
+            track_state: config.track_state,
         }));
         Ok(())
     }
@@ -1594,6 +1597,9 @@ impl X64FunctionCode {
         fsm: &mut FunctionStateMap,
         control_stack: &mut [ControlFrame],
     ) -> usize {
+        if !m.track_state {
+            return ::std::usize::MAX;
+        }
         let last_frame = control_stack.last_mut().unwrap();
         let mut diff = m.state.diff(&last_frame.state);
         diff.last = Some(last_frame.state_diff_id);

lib/singlepass-backend/src/machine.rs

@@ -13,6 +13,7 @@ pub struct Machine {
     stack_offset: MachineStackOffset,
     save_area_offset: Option<MachineStackOffset>,
     pub state: MachineState,
+    pub(crate) track_state: bool,
 }
 
 impl Machine {
@@ -23,6 +24,7 @@ impl Machine {
             stack_offset: MachineStackOffset(0),
             save_area_offset: None,
             state: x64::new_machine_state(),
+            track_state: true,
         }
     }
 

src/bin/wasmer.rs

@@ -112,10 +112,16 @@ struct Run {
     )]
     loader: Option<LoaderName>,
 
+    /// Path to previously saved instance image to resume.
     #[cfg(feature = "backend-singlepass")]
     #[structopt(long = "resume")]
     resume: Option<String>,
 
+    /// Whether or not state tracking should be disabled during compilation.
+    /// State tracking is necessary for tier switching and backtracing.
+    #[structopt(long = "no-track-state")]
+    no_track_state: bool,
+
     /// The command name is a string that will override the first argument passed
     /// to the wasm program. This is used in wapm to provide nicer output in
     /// help commands and error messages of the running wasm program
@@ -326,6 +332,8 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
         Backend::LLVM => return Err("the llvm backend is not enabled".to_string()),
     };
 
+    let track_state = !options.no_track_state;
+
     #[cfg(feature = "loader:kernel")]
     let is_kernel_loader = if let Some(LoaderName::Kernel) = options.loader {
         true
@@ -343,6 +351,7 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
                 symbol_map: em_symbol_map,
                 memory_bound_check_mode: MemoryBoundCheckMode::Disable,
                 enforce_stack_check: true,
+                track_state,
             },
             &*compiler,
         )
@@ -352,6 +361,7 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
             &wasm_binary[..],
             CompilerConfig {
                 symbol_map: em_symbol_map,
+                track_state,
                 ..Default::default()
             },
             &*compiler,
@@ -397,6 +407,7 @@ fn execute_wasm(options: &Run) -> Result<(), String> {
                         &wasm_binary[..],
                         CompilerConfig {
                             symbol_map: em_symbol_map,
+                            track_state,
                             ..Default::default()
                         },
                         &*compiler,