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py, vm: Replace save_ip, save_sp with code_state->{ip, sp}. 

This may seem a bit of a risky change, in that it may introduce crazy
bugs with respect to volatile variables in the VM loop.  But, I think it
should be fine: code_state points to some external memory, so the
compiler should always read/write to that memory when accessing the
ip/sp variables (ie not put them in registers).

Anyway, it passes all tests and improves on all efficiency fronts: about
2-4% faster (64-bit unix), 16 bytes less stack space per call (64-bit
unix) and slightly less executable size (unix and stmhal).

The reason it's more efficient is save_ip and save_sp were volatile
variables, so were anyway stored on the stack (in memory, not regs).
Thus converting them to code_state->{ip, sp} doesn't cost an extra
memory dereference (except maybe to get code_state, but that can be put
in a register and then made more efficient for other uses of it).
This commit is contained in:
Damien George 2014-06-01 12:32:28 +01:00
parent c7969857f4
commit c60a261ef0
1 changed files with 8 additions and 10 deletions
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18
py/vm.c
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@ -93,7 +93,7 @@ typedef enum {
#define PUSH_EXC_BLOCK() \
DECODE_ULABEL; /* except labels are always forward */ \
++exc_sp; \
exc_sp->opcode = *save_ip; \
exc_sp->opcode = *code_state->ip; \
exc_sp->handler = ip + unum; \
exc_sp->val_sp = MP_TAGPTR_MAKE(sp, currently_in_except_block); \
exc_sp->prev_exc = MP_OBJ_NULL; \
@ -224,7 +224,7 @@ mp_vm_return_kind_t mp_execute_bytecode2(mp_code_state *code_state, volatile mp_
#include "vmentrytable.h"
#define DISPATCH() do { \
TRACE(ip); \
save_ip = ip; \
code_state->ip = ip; \
goto *entry_table[*ip++]; \
} while(0)
#define ENTRY(op) entry_##op
@ -248,8 +248,6 @@ mp_vm_return_kind_t mp_execute_bytecode2(mp_code_state *code_state, volatile mp_
// variables that are visible to the exception handler (declared volatile)
volatile bool currently_in_except_block = MP_TAGPTR_TAG(code_state->exc_sp); // 0 or 1, to detect nested exceptions
mp_exc_stack_t *volatile exc_sp = MP_TAGPTR_PTR(code_state->exc_sp); // stack grows up, exc_sp points to top of stack
const byte *volatile save_ip = code_state->ip; // this is so we can access ip in the exception handler without making ip volatile (which means the compiler can't keep it in a register in the main loop)
mp_obj_t *volatile save_sp = code_state->sp; // this is so we can access sp in the exception handler when needed
// outer exception handling loop
for (;;) {
@ -281,7 +279,7 @@ dispatch_loop:
DISPATCH();
#else
TRACE(ip);
save_ip = ip;
code_state->ip = ip;
switch (*ip++) {
#endif
@ -686,7 +684,7 @@ unwind_jump:
ENTRY(MP_BC_FOR_ITER): {
DECODE_ULABEL; // the jump offset if iteration finishes; for labels are always forward
save_sp = sp;
code_state->sp = sp;
assert(TOP());
mp_obj_t value = mp_iternext_allow_raise(TOP());
if (value == MP_OBJ_STOP_ITERATION) {
@ -1024,12 +1022,12 @@ exception_handler:
// exception occurred
// check if it's a StopIteration within a for block
if (*save_ip == MP_BC_FOR_ITER && mp_obj_is_subclass_fast(mp_obj_get_type(nlr.ret_val), &mp_type_StopIteration)) {
const byte *ip = save_ip + 1;
if (*code_state->ip == MP_BC_FOR_ITER && mp_obj_is_subclass_fast(mp_obj_get_type(nlr.ret_val), &mp_type_StopIteration)) {
const byte *ip = code_state->ip + 1;
machine_uint_t unum;
DECODE_ULABEL; // the jump offset if iteration finishes; for labels are always forward
code_state->ip = ip + unum; // jump to after for-block
code_state->sp = save_sp - 1; // pop the exhausted iterator
code_state->sp -= 1; // pop the exhausted iterator
goto outer_dispatch_loop; // continue with dispatch loop
}
@ -1043,7 +1041,7 @@ exception_handler:
qstr source_file = code_info[4] | (code_info[5] << 8) | (code_info[6] << 16) | (code_info[7] << 24);
qstr block_name = code_info[8] | (code_info[9] << 8) | (code_info[10] << 16) | (code_info[11] << 24);
machine_uint_t source_line = 1;
machine_uint_t bc = save_ip - code_info - code_info_size;
machine_uint_t bc = code_state->ip - code_info - code_info_size;
//printf("find %lu %d %d\n", bc, code_info[12], code_info[13]);
for (const byte* ci = code_info + 12; *ci && bc >= ((*ci) & 31); ci++) {
bc -= *ci & 31;