tcg: Optimize qemu_ld/st by generating slow paths at the end of a block

Add optimized TCG qemu_ld/st generation which locates the code of TLB miss
cases at the end of a block after generating the other IRs.
Currently, this optimization supports only i386 and x86_64 hosts.

Signed-off-by: Yeongkyoon Lee <yeongkyoon.lee@samsung.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

tcg/i386/tcg-target.c

@@ -1002,6 +1002,17 @@ static const void *qemu_st_helpers[4] = {
     helper_stq_mmu,
 };
 
+static void add_qemu_ldst_label(TCGContext *s,
+                                int is_ld,
+                                int opc,
+                                int data_reg,
+                                int data_reg2,
+                                int addrlo_reg,
+                                int addrhi_reg,
+                                int mem_index,
+                                uint8_t *raddr,
+                                uint8_t **label_ptr);
+
 /* Perform the TLB load and compare.
 
    Inputs:
@@ -1060,19 +1071,19 @@ static inline void tcg_out_tlb_load(TCGContext *s, int addrlo_idx,
 
     tcg_out_mov(s, type, r1, addrlo);
 
-    /* jne label1 */
+    /* jne slow_path */
-    tcg_out8(s, OPC_JCC_short + JCC_JNE);
+    tcg_out_opc(s, OPC_JCC_long + JCC_JNE, 0, 0, 0);
     label_ptr[0] = s->code_ptr;
-    s->code_ptr++;
+    s->code_ptr += 4;
 
     if (TARGET_LONG_BITS > TCG_TARGET_REG_BITS) {
         /* cmp 4(r0), addrhi */
         tcg_out_modrm_offset(s, OPC_CMP_GvEv, args[addrlo_idx+1], r0, 4);
 
-        /* jne label1 */
+        /* jne slow_path */
-        tcg_out8(s, OPC_JCC_short + JCC_JNE);
+        tcg_out_opc(s, OPC_JCC_long + JCC_JNE, 0, 0, 0);
         label_ptr[1] = s->code_ptr;
-        s->code_ptr++;
+        s->code_ptr += 4;
     }
 
     /* TLB Hit.  */
@@ -1193,10 +1204,7 @@ static void tcg_out_qemu_ld(TCGContext *s, const TCGArg *args,
     int addrlo_idx;
 #if defined(CONFIG_SOFTMMU)
     int mem_index, s_bits;
-#if TCG_TARGET_REG_BITS == 32
+    uint8_t *label_ptr[2];
-    int stack_adjust;
-#endif
-    uint8_t *label_ptr[3];
 #endif
 
     data_reg = args[0];
@@ -1216,87 +1224,17 @@ static void tcg_out_qemu_ld(TCGContext *s, const TCGArg *args,
     /* TLB Hit.  */
     tcg_out_qemu_ld_direct(s, data_reg, data_reg2, TCG_REG_L1, 0, 0, opc);
 
-    /* jmp label2 */
+    /* Record the current context of a load into ldst label */
-    tcg_out8(s, OPC_JMP_short);
+    add_qemu_ldst_label(s,
-    label_ptr[2] = s->code_ptr;
+                        1,
-    s->code_ptr++;
+                        opc,
-
+                        data_reg,
-    /* TLB Miss.  */
+                        data_reg2,
-
+                        args[addrlo_idx],
-    /* label1: */
+                        args[addrlo_idx + 1],
-    *label_ptr[0] = s->code_ptr - label_ptr[0] - 1;
+                        mem_index,
-    if (TARGET_LONG_BITS > TCG_TARGET_REG_BITS) {
+                        s->code_ptr,
-        *label_ptr[1] = s->code_ptr - label_ptr[1] - 1;
+                        label_ptr);
-    }
-
-    /* XXX: move that code at the end of the TB */
-#if TCG_TARGET_REG_BITS == 32
-    tcg_out_pushi(s, mem_index);
-    stack_adjust = 4;
-    if (TARGET_LONG_BITS == 64) {
-        tcg_out_push(s, args[addrlo_idx + 1]);
-        stack_adjust += 4;
-    }
-    tcg_out_push(s, args[addrlo_idx]);
-    stack_adjust += 4;
-    tcg_out_push(s, TCG_AREG0);
-    stack_adjust += 4;
-#else
-    tcg_out_mov(s, TCG_TYPE_I64, tcg_target_call_iarg_regs[0], TCG_AREG0);
-    /* The second argument is already loaded with addrlo.  */
-    tcg_out_movi(s, TCG_TYPE_I32, tcg_target_call_iarg_regs[2], mem_index);
-#endif
-
-    tcg_out_calli(s, (tcg_target_long)qemu_ld_helpers[s_bits]);
-
-#if TCG_TARGET_REG_BITS == 32
-    if (stack_adjust == (TCG_TARGET_REG_BITS / 8)) {
-        /* Pop and discard.  This is 2 bytes smaller than the add.  */
-        tcg_out_pop(s, TCG_REG_ECX);
-    } else if (stack_adjust != 0) {
-        tcg_out_addi(s, TCG_REG_CALL_STACK, stack_adjust);
-    }
-#endif
-
-    switch(opc) {
-    case 0 | 4:
-        tcg_out_ext8s(s, data_reg, TCG_REG_EAX, P_REXW);
-        break;
-    case 1 | 4:
-        tcg_out_ext16s(s, data_reg, TCG_REG_EAX, P_REXW);
-        break;
-    case 0:
-        tcg_out_ext8u(s, data_reg, TCG_REG_EAX);
-        break;
-    case 1:
-        tcg_out_ext16u(s, data_reg, TCG_REG_EAX);
-        break;
-    case 2:
-        tcg_out_mov(s, TCG_TYPE_I32, data_reg, TCG_REG_EAX);
-        break;
-#if TCG_TARGET_REG_BITS == 64
-    case 2 | 4:
-        tcg_out_ext32s(s, data_reg, TCG_REG_EAX);
-        break;
-#endif
-    case 3:
-        if (TCG_TARGET_REG_BITS == 64) {
-            tcg_out_mov(s, TCG_TYPE_I64, data_reg, TCG_REG_RAX);
-        } else if (data_reg == TCG_REG_EDX) {
-            /* xchg %edx, %eax */
-            tcg_out_opc(s, OPC_XCHG_ax_r32 + TCG_REG_EDX, 0, 0, 0);
-            tcg_out_mov(s, TCG_TYPE_I32, data_reg2, TCG_REG_EAX);
-        } else {
-            tcg_out_mov(s, TCG_TYPE_I32, data_reg, TCG_REG_EAX);
-            tcg_out_mov(s, TCG_TYPE_I32, data_reg2, TCG_REG_EDX);
-        }
-        break;
-    default:
-        tcg_abort();
-    }
-
-    /* label2: */
-    *label_ptr[2] = s->code_ptr - label_ptr[2] - 1;
 #else
     {
         int32_t offset = GUEST_BASE;
@@ -1393,8 +1331,7 @@ static void tcg_out_qemu_st(TCGContext *s, const TCGArg *args,
     int addrlo_idx;
 #if defined(CONFIG_SOFTMMU)
     int mem_index, s_bits;
-    int stack_adjust;
+    uint8_t *label_ptr[2];
-    uint8_t *label_ptr[3];
 #endif
 
     data_reg = args[0];
@@ -1414,57 +1351,17 @@ static void tcg_out_qemu_st(TCGContext *s, const TCGArg *args,
     /* TLB Hit.  */
     tcg_out_qemu_st_direct(s, data_reg, data_reg2, TCG_REG_L1, 0, 0, opc);
 
-    /* jmp label2 */
+    /* Record the current context of a store into ldst label */
-    tcg_out8(s, OPC_JMP_short);
+    add_qemu_ldst_label(s,
-    label_ptr[2] = s->code_ptr;
+                        0,
-    s->code_ptr++;
+                        opc,
-
+                        data_reg,
-    /* TLB Miss.  */
+                        data_reg2,
-
+                        args[addrlo_idx],
-    /* label1: */
+                        args[addrlo_idx + 1],
-    *label_ptr[0] = s->code_ptr - label_ptr[0] - 1;
+                        mem_index,
-    if (TARGET_LONG_BITS > TCG_TARGET_REG_BITS) {
+                        s->code_ptr,
-        *label_ptr[1] = s->code_ptr - label_ptr[1] - 1;
+                        label_ptr);
-    }
-
-    /* XXX: move that code at the end of the TB */
-#if TCG_TARGET_REG_BITS == 32
-    tcg_out_pushi(s, mem_index);
-    stack_adjust = 4;
-    if (opc == 3) {
-        tcg_out_push(s, data_reg2);
-        stack_adjust += 4;
-    }
-    tcg_out_push(s, data_reg);
-    stack_adjust += 4;
-    if (TARGET_LONG_BITS == 64) {
-        tcg_out_push(s, args[addrlo_idx + 1]);
-        stack_adjust += 4;
-    }
-    tcg_out_push(s, args[addrlo_idx]);
-    stack_adjust += 4;
-    tcg_out_push(s, TCG_AREG0);
-    stack_adjust += 4;
-#else
-    tcg_out_mov(s, TCG_TYPE_I64, tcg_target_call_iarg_regs[0], TCG_AREG0);
-    /* The second argument is already loaded with addrlo.  */
-    tcg_out_mov(s, (opc == 3 ? TCG_TYPE_I64 : TCG_TYPE_I32),
-                tcg_target_call_iarg_regs[2], data_reg);
-    tcg_out_movi(s, TCG_TYPE_I32, tcg_target_call_iarg_regs[3], mem_index);
-    stack_adjust = 0;
-#endif
-
-    tcg_out_calli(s, (tcg_target_long)qemu_st_helpers[s_bits]);
-
-    if (stack_adjust == (TCG_TARGET_REG_BITS / 8)) {
-        /* Pop and discard.  This is 2 bytes smaller than the add.  */
-        tcg_out_pop(s, TCG_REG_ECX);
-    } else if (stack_adjust != 0) {
-        tcg_out_addi(s, TCG_REG_CALL_STACK, stack_adjust);
-    }
-
-    /* label2: */
-    *label_ptr[2] = s->code_ptr - label_ptr[2] - 1;
 #else
     {
         int32_t offset = GUEST_BASE;
@@ -1491,6 +1388,261 @@ static void tcg_out_qemu_st(TCGContext *s, const TCGArg *args,
 #endif
 }
 
+#if defined(CONFIG_SOFTMMU)
+/*
+ * Record the context of a call to the out of line helper code for the slow path
+ * for a load or store, so that we can later generate the correct helper code
+ */
+static void add_qemu_ldst_label(TCGContext *s,
+                                int is_ld,
+                                int opc,
+                                int data_reg,
+                                int data_reg2,
+                                int addrlo_reg,
+                                int addrhi_reg,
+                                int mem_index,
+                                uint8_t *raddr,
+                                uint8_t **label_ptr)
+{
+    int idx;
+    TCGLabelQemuLdst *label;
+
+    if (s->nb_qemu_ldst_labels >= TCG_MAX_QEMU_LDST) {
+        tcg_abort();
+    }
+
+    idx = s->nb_qemu_ldst_labels++;
+    label = (TCGLabelQemuLdst *)&s->qemu_ldst_labels[idx];
+    label->is_ld = is_ld;
+    label->opc = opc;
+    label->datalo_reg = data_reg;
+    label->datahi_reg = data_reg2;
+    label->addrlo_reg = addrlo_reg;
+    label->addrhi_reg = addrhi_reg;
+    label->mem_index = mem_index;
+    label->raddr = raddr;
+    label->label_ptr[0] = label_ptr[0];
+    if (TARGET_LONG_BITS > TCG_TARGET_REG_BITS) {
+        label->label_ptr[1] = label_ptr[1];
+    }
+}
+
+/*
+ * Generate code for the slow path for a load at the end of block
+ */
+static void tcg_out_qemu_ld_slow_path(TCGContext *s, TCGLabelQemuLdst *label)
+{
+    int s_bits;
+    int opc = label->opc;
+    int mem_index = label->mem_index;
+#if TCG_TARGET_REG_BITS == 32
+    int stack_adjust;
+    int addrlo_reg = label->addrlo_reg;
+    int addrhi_reg = label->addrhi_reg;
+#endif
+    int data_reg = label->datalo_reg;
+    int data_reg2 = label->datahi_reg;
+    uint8_t *raddr = label->raddr;
+    uint8_t **label_ptr = &label->label_ptr[0];
+
+    s_bits = opc & 3;
+
+    /* resolve label address */
+    *(uint32_t *)label_ptr[0] = (uint32_t)(s->code_ptr - label_ptr[0] - 4);
+    if (TARGET_LONG_BITS > TCG_TARGET_REG_BITS) {
+        *(uint32_t *)label_ptr[1] = (uint32_t)(s->code_ptr - label_ptr[1] - 4);
+    }
+
+#if TCG_TARGET_REG_BITS == 32
+    tcg_out_pushi(s, mem_index);
+    stack_adjust = 4;
+    if (TARGET_LONG_BITS == 64) {
+        tcg_out_push(s, addrhi_reg);
+        stack_adjust += 4;
+    }
+    tcg_out_push(s, addrlo_reg);
+    stack_adjust += 4;
+    tcg_out_push(s, TCG_AREG0);
+    stack_adjust += 4;
+#else
+    tcg_out_mov(s, TCG_TYPE_I64, tcg_target_call_iarg_regs[0], TCG_AREG0);
+    /* The second argument is already loaded with addrlo.  */
+    tcg_out_movi(s, TCG_TYPE_I32, tcg_target_call_iarg_regs[2], mem_index);
+#endif
+
+    /* Code generation of qemu_ld/st's slow path calling MMU helper
+
+       PRE_PROC ...
+       call MMU helper
+       jmp POST_PROC (2b) : short forward jump <- GETRA()
+       jmp next_code (5b) : dummy long backward jump which is never executed
+       POST_PROC ... : do post-processing <- GETRA() + 7
+       jmp next_code : jump to the code corresponding to next IR of qemu_ld/st
+    */
+
+    tcg_out_calli(s, (tcg_target_long)qemu_ld_helpers[s_bits]);
+
+    /* Jump to post-processing code */
+    tcg_out8(s, OPC_JMP_short);
+    tcg_out8(s, 5);
+    /* Dummy backward jump having information of fast path'pc for MMU helpers */
+    tcg_out8(s, OPC_JMP_long);
+    *(int32_t *)s->code_ptr = (int32_t)(raddr - s->code_ptr - 4);
+    s->code_ptr += 4;
+
+#if TCG_TARGET_REG_BITS == 32
+    if (stack_adjust == (TCG_TARGET_REG_BITS / 8)) {
+        /* Pop and discard.  This is 2 bytes smaller than the add.  */
+        tcg_out_pop(s, TCG_REG_ECX);
+    } else if (stack_adjust != 0) {
+        tcg_out_addi(s, TCG_REG_CALL_STACK, stack_adjust);
+    }
+#endif
+
+    switch(opc) {
+    case 0 | 4:
+        tcg_out_ext8s(s, data_reg, TCG_REG_EAX, P_REXW);
+        break;
+    case 1 | 4:
+        tcg_out_ext16s(s, data_reg, TCG_REG_EAX, P_REXW);
+        break;
+    case 0:
+        tcg_out_ext8u(s, data_reg, TCG_REG_EAX);
+        break;
+    case 1:
+        tcg_out_ext16u(s, data_reg, TCG_REG_EAX);
+        break;
+    case 2:
+        tcg_out_mov(s, TCG_TYPE_I32, data_reg, TCG_REG_EAX);
+        break;
+#if TCG_TARGET_REG_BITS == 64
+    case 2 | 4:
+        tcg_out_ext32s(s, data_reg, TCG_REG_EAX);
+        break;
+#endif
+    case 3:
+        if (TCG_TARGET_REG_BITS == 64) {
+            tcg_out_mov(s, TCG_TYPE_I64, data_reg, TCG_REG_RAX);
+        } else if (data_reg == TCG_REG_EDX) {
+            /* xchg %edx, %eax */
+            tcg_out_opc(s, OPC_XCHG_ax_r32 + TCG_REG_EDX, 0, 0, 0);
+            tcg_out_mov(s, TCG_TYPE_I32, data_reg2, TCG_REG_EAX);
+        } else {
+            tcg_out_mov(s, TCG_TYPE_I32, data_reg, TCG_REG_EAX);
+            tcg_out_mov(s, TCG_TYPE_I32, data_reg2, TCG_REG_EDX);
+        }
+        break;
+    default:
+        tcg_abort();
+    }
+
+    /* Jump to the code corresponding to next IR of qemu_st */
+    tcg_out_jmp(s, (tcg_target_long)raddr);
+}
+
+/*
+ * Generate code for the slow path for a store at the end of block
+ */
+static void tcg_out_qemu_st_slow_path(TCGContext *s, TCGLabelQemuLdst *label)
+{
+    int s_bits;
+    int stack_adjust;
+    int opc = label->opc;
+    int mem_index = label->mem_index;
+    int data_reg = label->datalo_reg;
+#if TCG_TARGET_REG_BITS == 32
+    int data_reg2 = label->datahi_reg;
+    int addrlo_reg = label->addrlo_reg;
+    int addrhi_reg = label->addrhi_reg;
+#endif
+    uint8_t *raddr = label->raddr;
+    uint8_t **label_ptr = &label->label_ptr[0];
+
+    s_bits = opc & 3;
+
+    /* resolve label address */
+    *(uint32_t *)label_ptr[0] = (uint32_t)(s->code_ptr - label_ptr[0] - 4);
+    if (TARGET_LONG_BITS > TCG_TARGET_REG_BITS) {
+        *(uint32_t *)label_ptr[1] = (uint32_t)(s->code_ptr - label_ptr[1] - 4);
+    }
+
+#if TCG_TARGET_REG_BITS == 32
+    tcg_out_pushi(s, mem_index);
+    stack_adjust = 4;
+    if (opc == 3) {
+        tcg_out_push(s, data_reg2);
+        stack_adjust += 4;
+    }
+    tcg_out_push(s, data_reg);
+    stack_adjust += 4;
+    if (TARGET_LONG_BITS == 64) {
+        tcg_out_push(s, addrhi_reg);
+        stack_adjust += 4;
+    }
+    tcg_out_push(s, addrlo_reg);
+    stack_adjust += 4;
+    tcg_out_push(s, TCG_AREG0);
+    stack_adjust += 4;
+#else
+    tcg_out_mov(s, TCG_TYPE_I64, tcg_target_call_iarg_regs[0], TCG_AREG0);
+    /* The second argument is already loaded with addrlo.  */
+    tcg_out_mov(s, (opc == 3 ? TCG_TYPE_I64 : TCG_TYPE_I32),
+                tcg_target_call_iarg_regs[2], data_reg);
+    tcg_out_movi(s, TCG_TYPE_I32, tcg_target_call_iarg_regs[3], mem_index);
+    stack_adjust = 0;
+#endif
+
+    /* Code generation of qemu_ld/st's slow path calling MMU helper
+
+       PRE_PROC ...
+       call MMU helper
+       jmp POST_PROC (2b) : short forward jump <- GETRA()
+       jmp next_code (5b) : dummy long backward jump which is never executed
+       POST_PROC ... : do post-processing <- GETRA() + 7
+       jmp next_code : jump to the code corresponding to next IR of qemu_ld/st
+    */
+
+    tcg_out_calli(s, (tcg_target_long)qemu_st_helpers[s_bits]);
+
+    /* Jump to post-processing code */
+    tcg_out8(s, OPC_JMP_short);
+    tcg_out8(s, 5);
+    /* Dummy backward jump having information of fast path'pc for MMU helpers */
+    tcg_out8(s, OPC_JMP_long);
+    *(int32_t *)s->code_ptr = (int32_t)(raddr - s->code_ptr - 4);
+    s->code_ptr += 4;
+
+    if (stack_adjust == (TCG_TARGET_REG_BITS / 8)) {
+        /* Pop and discard.  This is 2 bytes smaller than the add.  */
+        tcg_out_pop(s, TCG_REG_ECX);
+    } else if (stack_adjust != 0) {
+        tcg_out_addi(s, TCG_REG_CALL_STACK, stack_adjust);
+    }
+
+    /* Jump to the code corresponding to next IR of qemu_st */
+    tcg_out_jmp(s, (tcg_target_long)raddr);
+}
+
+/*
+ * Generate TB finalization at the end of block
+ */
+void tcg_out_tb_finalize(TCGContext *s)
+{
+    int i;
+    TCGLabelQemuLdst *label;
+
+    /* qemu_ld/st slow paths */
+    for (i = 0; i < s->nb_qemu_ldst_labels; i++) {
+        label = (TCGLabelQemuLdst *)&s->qemu_ldst_labels[i];
+        if (label->is_ld) {
+            tcg_out_qemu_ld_slow_path(s, label);
+        } else {
+            tcg_out_qemu_st_slow_path(s, label);
+        }
+    }
+}
+#endif  /* CONFIG_SOFTMMU */
+
 static inline void tcg_out_op(TCGContext *s, TCGOpcode opc,
                               const TCGArg *args, const int *const_args)
 {

tcg/tcg.c

@@ -299,6 +299,14 @@ void tcg_func_start(TCGContext *s)
 
     gen_opc_ptr = gen_opc_buf;
     gen_opparam_ptr = gen_opparam_buf;
+
+#if defined(CONFIG_QEMU_LDST_OPTIMIZATION) && defined(CONFIG_SOFTMMU)
+    /* Initialize qemu_ld/st labels to assist code generation at the end of TB
+       for TLB miss cases at the end of TB */
+    s->qemu_ldst_labels = tcg_malloc(sizeof(TCGLabelQemuLdst) *
+                                     TCG_MAX_QEMU_LDST);
+    s->nb_qemu_ldst_labels = 0;
+#endif
 }
 
 static inline void tcg_temp_alloc(TCGContext *s, int n)
@@ -2314,6 +2322,10 @@ static inline int tcg_gen_code_common(TCGContext *s, uint8_t *gen_code_buf,
 #endif
     }
  the_end:
+#if defined(CONFIG_QEMU_LDST_OPTIMIZATION) && defined(CONFIG_SOFTMMU)
+    /* Generate TB finalization at the end of block */
+    tcg_out_tb_finalize(s);
+#endif
     return -1;
 }
 

tcg/tcg.h

@@ -188,6 +188,24 @@ typedef tcg_target_ulong TCGArg;
    are aliases for target_ulong and host pointer sized values respectively.
  */
 
+#if defined(CONFIG_QEMU_LDST_OPTIMIZATION) && defined(CONFIG_SOFTMMU)
+/* Macros/structures for qemu_ld/st IR code optimization:
+   TCG_MAX_HELPER_LABELS is defined as same as OPC_BUF_SIZE in exec-all.h. */
+#define TCG_MAX_QEMU_LDST       640
+
+typedef struct TCGLabelQemuLdst {
+    int is_ld:1;            /* qemu_ld: 1, qemu_st: 0 */
+    int opc:4;
+    int addrlo_reg;         /* reg index for low word of guest virtual addr */
+    int addrhi_reg;         /* reg index for high word of guest virtual addr */
+    int datalo_reg;         /* reg index for low word to be loaded or stored */
+    int datahi_reg;         /* reg index for high word to be loaded or stored */
+    int mem_index;          /* soft MMU memory index */
+    uint8_t *raddr;         /* gen code addr of the next IR of qemu_ld/st IR */
+    uint8_t *label_ptr[2];  /* label pointers to be updated */
+} TCGLabelQemuLdst;
+#endif
+
 #ifdef CONFIG_DEBUG_TCG
 #define DEBUG_TCGV 1
 #endif
@@ -431,6 +449,13 @@ struct TCGContext {
     int temps_in_use;
     int goto_tb_issue_mask;
 #endif
+
+#if defined(CONFIG_QEMU_LDST_OPTIMIZATION) && defined(CONFIG_SOFTMMU)
+    /* labels info for qemu_ld/st IRs
+       The labels help to generate TLB miss case codes at the end of TB */
+    TCGLabelQemuLdst *qemu_ldst_labels;
+    int nb_qemu_ldst_labels;
+#endif
 };
 
 extern TCGContext tcg_ctx;
@@ -634,3 +659,8 @@ extern uint8_t *code_gen_prologue;
 #endif
 
 void tcg_register_jit(void *buf, size_t buf_size);
+
+#if defined(CONFIG_QEMU_LDST_OPTIMIZATION) && defined(CONFIG_SOFTMMU)
+/* Generate TB finalization at the end of block */
+void tcg_out_tb_finalize(TCGContext *s);
+#endif