support execute until segment (#1251)

Author: luffykai

crates/vm/src/arch/vm.rs

@@ -74,6 +74,18 @@ pub struct VmExecutorResult<SC: StarkGenericConfig> {
     pub final_memory: Option<VmMemoryState<Val<SC>>>,
 }
 
+pub struct VmExecutorNextSegmentState<F: PrimeField32> {
+    pub memory: MemoryImage<F>,
+    pub input: Streams<F>,
+    pub pc: u32,
+    pub segment_idx: usize,
+}
+
+pub struct VmExecutorOneSegmentResult<F: PrimeField32, VC: VmConfig<F>> {
+    pub segment: ExecutionSegment<F, VC>,
+    pub next_state: Option<VmExecutorNextSegmentState<F>>,
+}
+
 impl<F, VC> VmExecutor<F, VC>
 where
     F: PrimeField32,
@@ -110,70 +122,92 @@ where
         exe: impl Into<VmExe<F>>,
         input: impl Into<Streams<F>>,
     ) -> Result<Vec<ExecutionSegment<F, VC>>, ExecutionError> {
+        let mem_config = self.config.system().memory_config;
         let exe = exe.into();
-        let streams = input.into();
+        let mut streams = input.into();
         let mut segments = vec![];
-        let mem_config = self.config.system().memory_config;
+        let mut memory = AddressMap::from_iter(
+            mem_config.as_offset,
+            1 << mem_config.as_height,
+            1 << mem_config.pointer_max_bits,
+            exe.init_memory.clone(),
+        );
+        let mut pc = exe.pc_start;
+        let mut segment_idx = 0;
+
+        loop {
+            let mut one_segment_result =
+                self.execute_until_segment(exe.clone(), memory, streams, segment_idx, pc)?;
+            streams = one_segment_result.segment.chip_complex.take_streams();
+            segments.push(one_segment_result.segment);
+            if one_segment_result.next_state.is_none() {
+                break;
+            }
+            let next_state = one_segment_result.next_state.unwrap();
+            memory = next_state.memory;
+            pc = next_state.pc;
+            segment_idx = next_state.segment_idx;
+        }
+        tracing::debug!("Number of continuation segments: {}", segments.len());
+
+        Ok(segments)
+    }
+
+    /// Executes a program until a segmentation happens.
+    /// Returns the last segment and the vm state for next segment.
+    /// This is so that the tracegen and proving of this segment can be immediately started (on a separate machine).
+    pub fn execute_until_segment(
+        &self,
+        exe: impl Into<VmExe<F>>,
+        memory: MemoryImage<F>,
+        input: impl Into<Streams<F>>,
+        segment_idx: usize,
+        pc: u32,
+    ) -> Result<VmExecutorOneSegmentResult<F, VC>, ExecutionError> {
+        let exe = exe.into();
+        let streams = input.into();
         let mut segment = ExecutionSegment::new(
             &self.config,
             exe.program.clone(),
             streams,
-            Some(AddressMap::from_iter(
-                mem_config.as_offset,
-                1 << mem_config.as_height,
-                1 << mem_config.pointer_max_bits,
-                exe.init_memory.clone(),
-            )),
+            Some(memory),
             exe.fn_bounds.clone(),
         );
         if let Some(overridden_heights) = self.overridden_heights.as_ref() {
             segment.set_override_trace_heights(overridden_heights.clone());
         }
-        let mut pc = exe.pc_start;
-
-        loop {
-            // Used to add `segment` label to metrics
-            let _span = info_span!("execute_segment", segment = segments.len()).entered();
-            let state = metrics_span("execute_time_ms", || segment.execute_from_pc(pc))?;
-            pc = state.pc;
-
-            if state.is_terminated {
-                break;
-            }
-
-            assert!(
-                self.continuation_enabled(),
-                "multiple segments require to enable continuations"
-            );
-
-            assert_eq!(
-                pc,
-                segment.chip_complex.connector_chip().boundary_states[1]
-                    .unwrap()
-                    .pc
-            );
-
-            let final_memory = mem::take(&mut segment.final_memory)
-                .expect("final memory should be set in continuations segment");
-            let streams = segment.chip_complex.take_streams();
-
-            segments.push(segment);
-
-            segment = ExecutionSegment::new(
-                &self.config,
-                exe.program.clone(),
-                streams,
-                Some(final_memory),
-                exe.fn_bounds.clone(),
-            );
-            if let Some(overridden_heights) = self.overridden_heights.as_ref() {
-                segment.set_override_trace_heights(overridden_heights.clone());
-            }
+        let _span = info_span!("execute_segment", segment = segment_idx).entered();
+        let state = metrics_span("execute_time_ms", || segment.execute_from_pc(pc))?;
+
+        if state.is_terminated {
+            return Ok(VmExecutorOneSegmentResult {
+                segment,
+                next_state: None,
+            });
         }
-        segments.push(segment);
-        tracing::debug!("Number of continuation segments: {}", segments.len());
 
-        Ok(segments)
+        assert!(
+            self.continuation_enabled(),
+            "multiple segments require to enable continuations"
+        );
+        assert_eq!(
+            state.pc,
+            segment.chip_complex.connector_chip().boundary_states[1]
+                .unwrap()
+                .pc
+        );
+        let final_memory = mem::take(&mut segment.final_memory)
+            .expect("final memory should be set in continuations segment");
+        let streams = segment.chip_complex.take_streams();
+        Ok(VmExecutorOneSegmentResult {
+            segment,
+            next_state: Some(VmExecutorNextSegmentState {
+                memory: final_memory,
+                input: streams,
+                pc: state.pc,
+                segment_idx: segment_idx + 1,
+            }),
+        })
     }
 
     pub fn execute(