Tune bytecode quitting

* src/bytecode.c (BYTE_CODE_QUIT): Check for GC, too.  Do the
check only once every 256 times.  This should be good enough, and
improves performance significantly on x86-64 as branch-prediction
typically assumes checking will not be done so the instruction
pipeline stays fuller.
(exec_byte_code): Set up the quit counter.  Don’t call maybe_gc
directly, as BYTE_CODE_QUIT does that now.

1 files changed, 4 insertions, 10 deletions

diff --git a/src/bytecode.c b/src/bytecode.c
index 6be17e3fd3e..52f827f282a 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -368,6 +368,9 @@ relocate_byte_stack (void)
 
 #define BYTE_CODE_QUIT                                  \
   do {                                                  \
+    if (quitcounter++)                                  \
+      break;                                            \
+    maybe_gc ();                                        \
     if (!NILP (Vquit_flag) && NILP (Vinhibit_quit))     \
       {                                                 \
         Lisp_Object flag = Vquit_flag;                  \
@@ -446,6 +449,7 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
   stack.pc = stack.byte_string_start = SDATA (bytestr);
   if (MAX_ALLOCA / word_size <= XFASTINT (maxdepth))
     memory_full (SIZE_MAX);
+  unsigned char quitcounter = 0;
   int stack_items = XFASTINT (maxdepth) + 1;
   Lisp_Object *stack_base = alloca (stack_items * sizeof *top);
   Lisp_Object *stack_lim = stack_base + stack_items;
@@ -601,7 +605,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
         CASE (Bgotoifnil):
           {
             Lisp_Object v1;
-            maybe_gc ();
             op = FETCH2;
             v1 = POP;
             if (NILP (v1))
@@ -788,7 +791,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           NEXT;
 
         CASE (Bgoto):
-          maybe_gc ();
           BYTE_CODE_QUIT;
           op = FETCH2;    /* pc = FETCH2 loses since FETCH2 contains pc++ */
           CHECK_RANGE (op);
@@ -798,7 +800,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
         CASE (Bgotoifnonnil):
           {
             Lisp_Object v1;
-            maybe_gc ();
             op = FETCH2;
             v1 = POP;
             if (!NILP (v1))
@@ -811,7 +812,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           }
 
         CASE (Bgotoifnilelsepop):
-          maybe_gc ();
           op = FETCH2;
           if (NILP (TOP))
             {
@@ -823,7 +823,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           NEXT;
 
         CASE (Bgotoifnonnilelsepop):
-          maybe_gc ();
           op = FETCH2;
           if (!NILP (TOP))
             {
@@ -835,7 +834,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           NEXT;
 
         CASE (BRgoto):
-          maybe_gc ();
           BYTE_CODE_QUIT;
           stack.pc += (int) *stack.pc - 127;
           NEXT;
@@ -843,7 +841,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
         CASE (BRgotoifnil):
           {
             Lisp_Object v1;
-            maybe_gc ();
             v1 = POP;
             if (NILP (v1))
               {
@@ -857,7 +854,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
         CASE (BRgotoifnonnil):
           {
             Lisp_Object v1;
-            maybe_gc ();
             v1 = POP;
             if (!NILP (v1))
               {
@@ -869,7 +865,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           }
 
         CASE (BRgotoifnilelsepop):
-          maybe_gc ();
           op = *stack.pc++;
           if (NILP (TOP))
             {
@@ -880,7 +875,6 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth,
           NEXT;
 
         CASE (BRgotoifnonnilelsepop):
-          maybe_gc ();
           op = *stack.pc++;
           if (!NILP (TOP))
             {