Implement tier-2 JIT compiler to accelerate ISS

The T2C, designed for flexibility, efficiently transforms custom IR
within a chained block into LLVM IR. After the translation, the built
LLVM IR is offloaded to the LLVM backend, where it undergoes
optimization through several selected LLVM passes. Subsequently, the
optimized LLVM IR is passed to the LLVM execution engine, which compiles
the optimized LLVM IR and returns a function pointer to the generated
machine code. Because our design for T2C opts for a function pointer of
the generated machine code instead of storing it in the code cache, we
need not account for the binary format discrepancies among different
compilers. This process allows for the possibility of substituting LLVM
with alternative optimization frameworks if required.

.github/workflows/main.yml

@@ -44,6 +44,9 @@ jobs:
             sudo apt-get update -q -y
             sudo apt-get install -q -y libsdl2-dev libsdl2-mixer-dev
             .ci/riscv-toolchain-install.sh
+            wget https://apt.llvm.org/llvm.sh
+            sudo chmod +x ./llvm.sh
+            sudo ./llvm.sh 17
       shell: bash
     - name: default build
       run: make
@@ -65,14 +68,14 @@ jobs:
             make distclean ENABLE_GDBSTUB=1 gdbstub-test
     - name: JIT test
       run: |
-            make clean && make ENABLE_JIT=1 check -j$(nproc)
-            make clean && make ENABLE_EXT_A=0 ENABLE_JIT=1 check -j$(nproc)
-            make clean && make ENABLE_EXT_F=0 ENABLE_JIT=1 check -j$(nproc)
-            make clean && make ENABLE_EXT_C=0 ENABLE_JIT=1 check -j$(nproc)
+            make ENABLE_JIT=1 clean && make ENABLE_JIT=1 check -j$(nproc)
+            make ENABLE_JIT=1 clean && make ENABLE_EXT_A=0 ENABLE_JIT=1 check -j$(nproc)
+            make ENABLE_JIT=1 clean && make ENABLE_EXT_F=0 ENABLE_JIT=1 check -j$(nproc)
+            make ENABLE_JIT=1 clean && make ENABLE_EXT_C=0 ENABLE_JIT=1 check -j$(nproc)
     - name: undefined behavior test
       run: |
             make clean && make ENABLE_UBSAN=1 check -j$(nproc)
-            make clean && make ENABLE_JIT=1 ENABLE_UBSAN=1 check -j$(nproc)
+            make ENABLE_JIT=1 clean clean && make ENABLE_JIT=1 ENABLE_UBSAN=1 check -j$(nproc)
 
   host-arm64:
     needs: [detect-code-related-file-changes]
@@ -91,18 +94,21 @@ jobs:
         # No 'sudo' is available
         install: |
           apt-get update -q -y
-          apt-get install -q -y git build-essential libsdl2-dev libsdl2-mixer-dev
+          apt-get install -q -y git build-essential libsdl2-dev libsdl2-mixer-dev lsb-release wget software-properties-common gnupg
           git config --global --add safe.directory ${{ github.workspace }}
           git config --global --add safe.directory ${{ github.workspace }}/src/softfloat
           git config --global --add safe.directory ${{ github.workspace }}/src/mini-gdbstub
+          wget https://apt.llvm.org/llvm.sh
+          chmod +x ./llvm.sh
+          ./llvm.sh 17
         # Append custom commands here
         run: |
           make -j$(nproc)
           make check -j$(nproc)
-          make clean && make ENABLE_JIT=1 check -j$(nproc)
-          make clean && make ENABLE_EXT_A=0 ENABLE_JIT=1 check -j$(nproc)
-          make clean && make ENABLE_EXT_F=0 ENABLE_JIT=1 check -j$(nproc)
-          make clean && make ENABLE_EXT_C=0 ENABLE_JIT=1 check -j$(nproc)
+          make ENABLE_JIT=1 clean && make ENABLE_JIT=1 check -j$(nproc)
+          make ENABLE_JIT=1 clean && make ENABLE_EXT_A=0 ENABLE_JIT=1 check -j$(nproc)
+          make ENABLE_JIT=1 clean && make ENABLE_EXT_F=0 ENABLE_JIT=1 check -j$(nproc)
+          make ENABLE_JIT=1 clean && make ENABLE_EXT_C=0 ENABLE_JIT=1 check -j$(nproc)
 
   coding-style:
     needs: [detect-code-related-file-changes]
@@ -132,7 +138,8 @@ jobs:
     - name: run scan-build without JIT
       run: make distclean && scan-build -v -o ~/scan-build --status-bugs --use-cc=clang --force-analyze-debug-code --show-description -analyzer-config stable-report-filename=true -enable-checker valist,nullability make ENABLE_EXT_F=0 ENABLE_SDL=0 ENABLE_JIT=0
     - name: run scan-build with JIT
-      run: make distclean && scan-build -v -o ~/scan-build --status-bugs --use-cc=clang --force-analyze-debug-code --show-description -analyzer-config stable-report-filename=true -enable-checker valist,nullability make ENABLE_EXT_F=0 ENABLE_SDL=0 ENABLE_JIT=1
+      run: |
+          make ENABLE_JIT=1 distclean && scan-build -v -o ~/scan-build --status-bugs --use-cc=clang --force-analyze-debug-code --show-description -analyzer-config stable-report-filename=true -enable-checker valist,nullability make ENABLE_EXT_F=0 ENABLE_SDL=0 ENABLE_JIT=1
 
   compliance-test:
     needs: [detect-code-related-file-changes]

Makefile

@@ -125,7 +125,32 @@ endif
 ENABLE_JIT ?= 0
 $(call set-feature, JIT)
 ifeq ($(call has, JIT), 1)
-OBJS_EXT += jit.o
+OBJS_EXT += jit.o 
+# tier-2 JIT compiler powered LLVM
+LLVM_CONFIG = llvm-config-17
+LLVM_CONFIG := $(shell which $(LLVM_CONFIG))
+ifndef LLVM_CONFIG
+# Try Homebrew on macOS
+LLVM_CONFIG = /opt/homebrew/opt/llvm@17/bin/llvm-config
+LLVM_CONFIG := $(shell which $(LLVM_CONFIG))
+ifdef LLVM_CONFIG
+LDFLAGS += -L/opt/homebrew/opt/llvm@17/lib
+endif
+endif
+ifneq ("$(LLVM_CONFIG)", "")
+ifneq ("$(findstring -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS, "$(shell $(LLVM_CONFIG) --cflags)")", "")
+ENABLE_T2C := 1
+$(call set-feature, T2C)
+OBJS_EXT += t2c.o
+CFLAGS += -g $(shell $(LLVM_CONFIG) --cflags)
+LDFLAGS += $(shell $(LLVM_CONFIG) --libs)
+else
+ENABLE_T2C := 0
+$(call set-feature, T2C)
+$(warning No llvm-config-17 installed. Check llvm-config-17 installation in advance)
+endif
+endif
+
 ifneq ($(processor),$(filter $(processor),x86_64 aarch64 arm64))
 $(error JIT mode only supports for x64 and arm64 target currently.)
 endif
@@ -136,6 +161,10 @@ src/rv32_jit.c:
 $(OUT)/jit.o: src/jit.c src/rv32_jit.c
 	$(VECHO) "  CC\t$@\n"
 	$(Q)$(CC) -o $@ $(CFLAGS) -c -MMD -MF $@.d $<
+
+$(OUT)/t2c.o: src/t2c.c src/t2c_template.c
+	$(VECHO) "  CC\t$@\n"
+	$(Q)$(CC) -o $@ $(CFLAGS) -c -MMD -MF $@.d $<
 endif
 # For tail-call elimination, we need a specific set of build flags applied.
 # FIXME: On macOS + Apple Silicon, -fno-stack-protector might have a negative impact.

README.md

@@ -30,7 +30,7 @@ Features:
 * Implementation of commonly used newlib system calls
 * Experimental SDL-based display/event/audio system calls for running video games
 * Support for remote GDB debugging
-* Experimental JIT compiler for performance boost while maintaining a small footprint
+* Tiered JIT compilation for performance boost while maintaining a small footprint
 
 ## Build and Verify
 
@@ -40,6 +40,12 @@ and [SDL2_Mixer library](https://wiki.libsdl.org/SDL2_mixer) installed.
 * macOS: `brew install sdl2 sdl2_mixer`
 * Ubuntu Linux / Debian: `sudo apt install libsdl2-dev libsdl2-mixer-dev`
 
+### JIT compiler
+The tier-2 JIT compiler in `rv32emu` leverages LLVM for powerful optimization. Therefore, the target system must have [`LLVM`](https://llvm.org/) installed, with version 17 recommended. If `LLVM` is not installed, only the tier-1 JIT compiler will be used for performance enhancement.
+
+* macOS: `brew install llvm@17`
+* Ubuntu Linux / Debian: `sudo apt-get install llvm-17`
+
 Build the emulator.
 ```shell
 $ make

src/emulate.c

@@ -304,7 +304,9 @@ static block_t *block_alloc(riscv_t *rv)
 #if RV32_HAS(JIT)
     block->translatable = true;
     block->hot = false;
+    block->hot2 = false;
     block->has_loops = false;
+    block->n_invoke = 0;
     INIT_LIST_HEAD(&block->list);
 #endif
     return block;
@@ -911,8 +913,6 @@ static bool runtime_profiler(riscv_t *rv, block_t *block)
         return true;
     return false;
 }
-
-typedef void (*exec_block_func_t)(riscv_t *rv, uintptr_t);
 #endif
 
 void rv_step(void *arg)
@@ -985,15 +985,31 @@ void rv_step(void *arg)
         }
         last_pc = rv->PC;
 #if RV32_HAS(JIT)
-        /* execute by tier-1 JIT compiler */
+#if RV32_HAS(T2C)
+        /* executed through the tier-2 JIT compiler */
+        if (block->hot2) {
+            ((exec_t2c_func_t) block->func)(rv);
+            prev = NULL;
+            continue;
+        } /* check if the execution path is strong hotspot */
+        if (block->n_invoke >= THRESHOLD) {
+            t2c_compile(block,
+                        (uint64_t) ((memory_t *) PRIV(rv)->mem)->mem_base);
+            ((exec_t2c_func_t) block->func)(rv);
+            prev = NULL;
+            continue;
+        }
+#endif
+        /* executed through the tier-1 JIT compiler */
         struct jit_state *state = rv->jit_state;
         if (block->hot) {
+            block->n_invoke++;
             ((exec_block_func_t) state->buf)(
                 rv, (uintptr_t) (state->buf + block->offset));
             prev = NULL;
             continue;
-        } /* check if using frequency of block exceed threshold */
-        else if (block->translatable && runtime_profiler(rv, block)) {
+        } /* check if the execution path is potential hotspot */
+        if (block->translatable && runtime_profiler(rv, block)) {
             jit_translate(rv, block);
             ((exec_block_func_t) state->buf)(
                 rv, (uintptr_t) (state->buf + block->offset));

src/feature.h

@@ -52,5 +52,10 @@
 #define RV32_FEATURE_JIT 0
 #endif
 
+/* Experimental tier-2 just-in-time compiler */
+#ifndef RV32_FEATURE_T2C
+#define RV32_FEATURE_T2C 0
+#endif
+
 /* Feature test macro */
 #define RV32_HAS(x) RV32_FEATURE_##x

src/jit.h

@@ -48,3 +48,9 @@ struct host_reg {
 struct jit_state *jit_state_init(size_t size);
 void jit_state_exit(struct jit_state *state);
 void jit_translate(riscv_t *rv, block_t *block);
+typedef void (*exec_block_func_t)(riscv_t *rv, uintptr_t);
+
+#if RV32_HAS(T2C)
+void t2c_compile(block_t *block, uint64_t mem_base);
+typedef void (*exec_t2c_func_t)(riscv_t *);
+#endif

src/riscv_private.h

@@ -65,11 +65,14 @@ typedef struct block {
 
     rv_insn_t *ir_head, *ir_tail; /**< the first and last ir for this block */
 #if RV32_HAS(JIT)
-    bool hot; /**< Determine the block is hotspot or not */
-    uint32_t offset;
+    bool hot;  /**< Determine the block is potential hotspot or not */
+    bool hot2; /**< Determine the block is strong hotspot or not */
     bool
         translatable; /**< Determine the block has RV32AF insturctions or not */
     bool has_loops;   /**< Determine the block has loop or not */
+    uint32_t offset;  /**< The machine code offset in T1 code cache */
+    uint32_t n_invoke; /**< The invoking times of T1 machine code */
+    void *func;        /**< The function pointer of T2 machine code */
     struct list_head list;
 #endif
 } block_t;