tcg: Reorg TCGOp chaining

Instead of using -1 as end of chain, use 0, and link through the 0
entry as a fully circular double-linked list.
Reviewed-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

include/exec/gen-icount.h

@@ -59,7 +59,7 @@ static void gen_tb_end(TranslationBlock *tb, int num_insns)
     }
 
     /* Terminate the linked list.  */
-    tcg_ctx.gen_op_buf[tcg_ctx.gen_last_op_idx].next = -1;
+    tcg_ctx.gen_op_buf[tcg_ctx.gen_op_buf[0].prev].next = 0;
 }
 
 static inline void gen_io_start(void)

tcg/optimize.c

@@ -103,11 +103,7 @@ static TCGOp *insert_op_before(TCGContext *s, TCGOp *old_op,
         .prev = prev,
         .next = next
     };
-    if (prev >= 0) {
-        s->gen_op_buf[prev].next = oi;
-    } else {
-        s->gen_first_op_idx = oi;
-    }
+    s->gen_op_buf[prev].next = oi;
     old_op->prev = oi;
 
     return new_op;
@@ -583,7 +579,7 @@ void tcg_optimize(TCGContext *s)
     nb_globals = s->nb_globals;
     reset_all_temps(nb_temps);
 
-    for (oi = s->gen_first_op_idx; oi >= 0; oi = oi_next) {
+    for (oi = s->gen_op_buf[0].next; oi != 0; oi = oi_next) {
         tcg_target_ulong mask, partmask, affected;
         int nb_oargs, nb_iargs, i;
         TCGArg tmp;

tcg/tcg-op.c

@@ -52,7 +52,7 @@ static void tcg_emit_op(TCGContext *ctx, TCGOpcode opc, int args)
     int pi = oi - 1;
 
     tcg_debug_assert(oi < OPC_BUF_SIZE);
-    ctx->gen_last_op_idx = oi;
+    ctx->gen_op_buf[0].prev = oi;
     ctx->gen_next_op_idx = ni;
 
     ctx->gen_op_buf[oi] = (TCGOp){

tcg/tcg.c

@@ -438,9 +438,9 @@ void tcg_func_start(TCGContext *s)
     s->goto_tb_issue_mask = 0;
 #endif
 
-    s->gen_first_op_idx = 0;
-    s->gen_last_op_idx = -1;
-    s->gen_next_op_idx = 0;
+    s->gen_op_buf[0].next = 1;
+    s->gen_op_buf[0].prev = 0;
+    s->gen_next_op_idx = 1;
     s->gen_next_parm_idx = 0;
 
     s->be = tcg_malloc(sizeof(TCGBackendData));
@@ -869,7 +869,7 @@ void tcg_gen_callN(TCGContext *s, void *func, TCGArg ret,
     /* Make sure the calli field didn't overflow.  */
     tcg_debug_assert(s->gen_op_buf[i].calli == real_args);
 
-    s->gen_last_op_idx = i;
+    s->gen_op_buf[0].prev = i;
     s->gen_next_op_idx = i + 1;
     s->gen_next_parm_idx = pi;
 
@@ -1021,7 +1021,7 @@ void tcg_dump_ops(TCGContext *s)
     TCGOp *op;
     int oi;
 
-    for (oi = s->gen_first_op_idx; oi >= 0; oi = op->next) {
+    for (oi = s->gen_op_buf[0].next; oi != 0; oi = op->next) {
         int i, k, nb_oargs, nb_iargs, nb_cargs;
         const TCGOpDef *def;
         const TCGArg *args;
@@ -1033,7 +1033,7 @@ void tcg_dump_ops(TCGContext *s)
         args = &s->gen_opparam_buf[op->args];
 
         if (c == INDEX_op_insn_start) {
-            qemu_log("%s ----", oi != s->gen_first_op_idx ? "\n" : "");
+            qemu_log("%s ----", oi != s->gen_op_buf[0].next ? "\n" : "");
 
             for (i = 0; i < TARGET_INSN_START_WORDS; ++i) {
                 target_ulong a;
@@ -1298,18 +1298,13 @@ void tcg_op_remove(TCGContext *s, TCGOp *op)
     int next = op->next;
     int prev = op->prev;
 
-    if (next >= 0) {
-        s->gen_op_buf[next].prev = prev;
-    } else {
-        s->gen_last_op_idx = prev;
-    }
-    if (prev >= 0) {
-        s->gen_op_buf[prev].next = next;
-    } else {
-        s->gen_first_op_idx = next;
-    }
+    /* We should never attempt to remove the list terminator.  */
+    tcg_debug_assert(op != &s->gen_op_buf[0]);
+
+    s->gen_op_buf[next].prev = prev;
+    s->gen_op_buf[prev].next = next;
 
-    memset(op, -1, sizeof(*op));
+    memset(op, 0, sizeof(*op));
 
 #ifdef CONFIG_PROFILER
     s->del_op_count++;
@@ -1356,7 +1351,7 @@ static void tcg_liveness_analysis(TCGContext *s)
     mem_temps = tcg_malloc(s->nb_temps);
     tcg_la_func_end(s, dead_temps, mem_temps);
 
-    for (oi = s->gen_last_op_idx; oi >= 0; oi = oi_prev) {
+    for (oi = s->gen_op_buf[0].prev; oi != 0; oi = oi_prev) {
         int i, nb_iargs, nb_oargs;
         TCGOpcode opc_new, opc_new2;
         bool have_opc_new2;
@@ -2351,7 +2346,7 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb)
     {
         int n;
 
-        n = s->gen_last_op_idx + 1;
+        n = s->gen_op_buf[0].prev + 1;
         s->op_count += n;
         if (n > s->op_count_max) {
             s->op_count_max = n;
@@ -2410,7 +2405,7 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb)
     tcg_out_tb_init(s);
 
     num_insns = -1;
-    for (oi = s->gen_first_op_idx; oi >= 0; oi = oi_next) {
+    for (oi = s->gen_op_buf[0].next; oi != 0; oi = oi_next) {
         TCGOp * const op = &s->gen_op_buf[oi];
         TCGArg * const args = &s->gen_opparam_buf[op->args];
         TCGOpcode opc = op->opc;

tcg/tcg.h

@@ -590,17 +590,21 @@ typedef struct TCGOp {
     unsigned callo  : 2;
     unsigned calli  : 6;
 
-    /* Index of the arguments for this op, or -1 for zero-operand ops.  */
-    signed args     : 16;
+    /* Index of the arguments for this op, or 0 for zero-operand ops.  */
+    unsigned args   : 16;
 
-    /* Index of the prex/next op, or -1 for the end of the list.  */
-    signed prev     : 16;
-    signed next     : 16;
+    /* Index of the prev/next op, or 0 for the end of the list.  */
+    unsigned prev   : 16;
+    unsigned next   : 16;
 } TCGOp;
 
-QEMU_BUILD_BUG_ON(NB_OPS > 0xff);
-QEMU_BUILD_BUG_ON(OPC_BUF_SIZE >= 0x7fff);
-QEMU_BUILD_BUG_ON(OPPARAM_BUF_SIZE >= 0x7fff);
+/* Make sure operands fit in the bitfields above.  */
+QEMU_BUILD_BUG_ON(NB_OPS > (1 << 8));
+QEMU_BUILD_BUG_ON(OPC_BUF_SIZE > (1 << 16));
+QEMU_BUILD_BUG_ON(OPPARAM_BUF_SIZE > (1 << 16));
+
+/* Make sure that we don't overflow 64 bits without noticing.  */
+QEMU_BUILD_BUG_ON(sizeof(TCGOp) > 8);
 
 struct TCGContext {
     uint8_t *pool_cur, *pool_end;
@@ -653,8 +657,6 @@ struct TCGContext {
     int goto_tb_issue_mask;
 #endif
 
-    int gen_first_op_idx;
-    int gen_last_op_idx;
     int gen_next_op_idx;
     int gen_next_parm_idx;