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[Guile-commits] 04/12: VM caches address of local 0 instead of FP
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From: |
Andy Wingo |
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Subject: |
[Guile-commits] 04/12: VM caches address of local 0 instead of FP |
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Date: |
Wed, 21 Oct 2015 13:13:30 +0000 |
wingo pushed a commit to branch master
in repository guile.
commit aa9f6b00827bd0c1a2f11274191f49b0ad31926d
Author: Andy Wingo <address@hidden>
Date: Sun Oct 18 19:54:58 2015 +0200
VM caches address of local 0 instead of FP
* libguile/vm-engine.c (vm_engine): Cache the address of local 0 instead
of the FP. This makes locals access a bit cheaper, but we still have
to negate the index. The right fix is to index relative to the SP
instead. That's a more involved change, so we punt until later.
---
libguile/vm-engine.c | 122 +++++++++++++++++++++++++++----------------------
1 files changed, 67 insertions(+), 55 deletions(-)
diff --git a/libguile/vm-engine.c b/libguile/vm-engine.c
index f6cb0c4..9415de5 100644
--- a/libguile/vm-engine.c
+++ b/libguile/vm-engine.c
@@ -107,7 +107,7 @@
{ \
SYNC_IP (); \
exp; \
- CACHE_FP (); \
+ CACHE_LOCALS (); \
} \
} while (0)
#else
@@ -128,37 +128,39 @@
RUN_HOOK0 (abort)
#define VM_HANDLE_INTERRUPTS \
- SCM_ASYNC_TICK_WITH_GUARD_CODE (thread, SYNC_IP (), CACHE_FP ())
+ SCM_ASYNC_TICK_WITH_GUARD_CODE (thread, SYNC_IP (), CACHE_LOCALS ())
/* Virtual Machine
The VM has three state bits: the instruction pointer (IP), the frame
- pointer (FP), and the stack pointer (SP). We cache the first two of
- these in machine registers, local to the VM, because they are used
- extensively by the VM. As the SP is used more by code outside the VM
- than by the VM itself, we don't bother caching it locally.
-
- Since the FP changes infrequently, relative to the IP, we keep vp->fp
- in sync with the local FP. This would be a big lose for the IP,
- though, so instead of updating vp->ip all the time, we call SYNC_IP
- whenever we would need to know the IP of the top frame. In practice,
- we need to SYNC_IP whenever we call out of the VM to a function that
- would like to walk the stack, perhaps as the result of an
- exception.
+ pointer (FP), and the stack pointer (SP). We cache the IP in a
+ machine register, local to the VM, because it is used extensively by
+ the VM. We cache the address of local 0 too, for now; when we change
+ to reference variables relative to the SP we'll cache the SP instead.
+ As it is, the SP is used more by code outside the VM than by the VM
+ itself, we don't bother caching it locally.
+
+ Keeping vp->ip in sync with the local IP would be a big lose, as it
+ is updated so often. Instead of updating vp->ip all the time, we
+ call SYNC_IP whenever we would need to know the IP of the top frame.
+ In practice, we need to SYNC_IP whenever we call out of the VM to a
+ function that would like to walk the stack, perhaps as the result of
+ an exception.
One more thing. We allow the stack to move, when it expands.
Therefore if you call out to a C procedure that could call Scheme
code, or otherwise push anything on the stack, you will need to
- CACHE_FP afterwards to restore the possibly-changed FP. */
+ CACHE_LOCALS afterwards to restore the possibly-changed address of
+ local 0. */
#define SYNC_IP() vp->ip = (ip)
-#define CACHE_FP() fp = (vp->fp)
+#define CACHE_LOCALS() locals = (vp->fp - 1)
#define CACHE_REGISTER() \
do { \
ip = vp->ip; \
- fp = vp->fp; \
+ CACHE_LOCALS (); \
} while (0)
@@ -179,7 +181,7 @@
{ \
SYNC_IP (); \
vm_expand_stack (vp, new_sp); \
- CACHE_FP (); \
+ CACHE_LOCALS (); \
} \
else \
vp->sp_min_since_gc = vp->sp = new_sp; \
@@ -246,9 +248,15 @@
case opcode:
#endif
-#define LOCAL_ADDRESS(i) SCM_FRAME_SLOT (fp, i)
-#define LOCAL_REF(i) SCM_FRAME_LOCAL (fp, i)
-#define LOCAL_SET(i,o) SCM_FRAME_LOCAL (fp, i) = o
+// This "locals + 1" is actually an optimization, because vp->fp points
+// on before the zeroeth local. The result is to reference locals[-i].
+// In the future we should change to reference locals relative to the SP
+// and cache the SP instead, which would give direct (non-negated)
+// indexing off the SP, which is more in line with addressing modes
+// supported by common CPUs.
+#define LOCAL_ADDRESS(i) SCM_FRAME_SLOT (locals + 1, i)
+#define LOCAL_REF(i) SCM_FRAME_LOCAL (locals + 1, i)
+#define LOCAL_SET(i,o) SCM_FRAME_LOCAL (locals + 1, i) = o
#define VARIABLE_REF(v) SCM_VARIABLE_REF (v)
#define VARIABLE_SET(v,o) SCM_VARIABLE_SET (v, o)
@@ -260,9 +268,10 @@
union scm_vm_stack_element *old_fp; \
VM_HANDLE_INTERRUPTS; \
ALLOC_FRAME (2); \
- old_fp = fp; \
- ip = SCM_FRAME_RETURN_ADDRESS (fp); \
- fp = vp->fp = SCM_FRAME_DYNAMIC_LINK (fp); \
+ old_fp = vp->fp; \
+ ip = SCM_FRAME_RETURN_ADDRESS (vp->fp); \
+ vp->fp = SCM_FRAME_DYNAMIC_LINK (vp->fp); \
+ CACHE_LOCALS (); \
/* Clear frame. */ \
old_fp[0].scm = SCM_BOOL_F; \
old_fp[1].scm = SCM_BOOL_F; \
@@ -280,9 +289,9 @@
SCM vals = vals_; \
VM_HANDLE_INTERRUPTS; \
ALLOC_FRAME (3); \
- SCM_FRAME_LOCAL (fp, 0) = vm_builtin_apply; \
- SCM_FRAME_LOCAL (fp, 1) = vm_builtin_values; \
- SCM_FRAME_LOCAL (fp, 2) = vals; \
+ SCM_FRAME_LOCAL (vp->fp, 0) = vm_builtin_apply; \
+ SCM_FRAME_LOCAL (vp->fp, 1) = vm_builtin_values; \
+ SCM_FRAME_LOCAL (vp->fp, 2) = vals; \
ip = (scm_t_uint32 *) vm_builtin_apply_code; \
goto op_tail_apply; \
} while (0)
@@ -355,7 +364,7 @@
SCM res; \
SYNC_IP (); \
res = srel (x, y); \
- CACHE_FP (); \
+ CACHE_LOCALS (); \
if ((ip[1] & 0x1) ? scm_is_false (res) : scm_is_true (res)) \
{ \
scm_t_int32 offset = ip[1]; \
@@ -382,7 +391,7 @@
#define RETURN(x) \
do { LOCAL_SET (dst, x); NEXT (1); } while (0)
#define RETURN_EXP(exp) \
- do { SCM __x; SYNC_IP (); __x = exp; CACHE_FP (); RETURN (__x); } while (0)
+ do { SCM __x; SYNC_IP (); __x = exp; CACHE_LOCALS (); RETURN (__x); } while
(0)
/* The maximum/minimum tagged integers. */
#define INUM_MAX \
@@ -429,7 +438,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
/* Frame pointer: A pointer into the stack, off of which we index
arguments and local variables. Pushed at function calls, popped on
returns. */
- register union scm_vm_stack_element *fp FP_REG;
+ register union scm_vm_stack_element *locals FP_REG;
/* Current opcode: A cache of *ip. */
register scm_t_uint32 op;
@@ -524,9 +533,9 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
ret = scm_values (ret);
}
- vp->ip = SCM_FRAME_RETURN_ADDRESS (fp);
- vp->sp = SCM_FRAME_PREVIOUS_SP (fp);
- vp->fp = SCM_FRAME_DYNAMIC_LINK (fp);
+ vp->ip = SCM_FRAME_RETURN_ADDRESS (vp->fp);
+ vp->sp = SCM_FRAME_PREVIOUS_SP (vp->fp);
+ vp->fp = SCM_FRAME_DYNAMIC_LINK (vp->fp);
return ret;
}
@@ -556,10 +565,11 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
PUSH_CONTINUATION_HOOK ();
- old_fp = fp;
- fp = vp->fp = SCM_FRAME_SLOT (old_fp, proc - 1);
- SCM_FRAME_SET_DYNAMIC_LINK (fp, old_fp);
- SCM_FRAME_SET_RETURN_ADDRESS (fp, ip + 2);
+ old_fp = vp->fp;
+ vp->fp = SCM_FRAME_SLOT (old_fp, proc - 1);
+ CACHE_LOCALS ();
+ SCM_FRAME_SET_DYNAMIC_LINK (vp->fp, old_fp);
+ SCM_FRAME_SET_RETURN_ADDRESS (vp->fp, ip + 2);
RESET_FRAME (nlocals);
@@ -597,10 +607,11 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
PUSH_CONTINUATION_HOOK ();
- old_fp = fp;
- fp = vp->fp = SCM_FRAME_SLOT (old_fp, proc - 1);
- SCM_FRAME_SET_DYNAMIC_LINK (fp, old_fp);
- SCM_FRAME_SET_RETURN_ADDRESS (fp, ip + 3);
+ old_fp = vp->fp;
+ vp->fp = SCM_FRAME_SLOT (old_fp, proc - 1);
+ CACHE_LOCALS ();
+ SCM_FRAME_SET_DYNAMIC_LINK (vp->fp, old_fp);
+ SCM_FRAME_SET_RETURN_ADDRESS (vp->fp, ip + 3);
RESET_FRAME (nlocals);
@@ -759,9 +770,10 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
VM_HANDLE_INTERRUPTS;
- old_fp = fp;
- ip = SCM_FRAME_RETURN_ADDRESS (fp);
- fp = vp->fp = SCM_FRAME_DYNAMIC_LINK (fp);
+ old_fp = vp->fp;
+ ip = SCM_FRAME_RETURN_ADDRESS (vp->fp);
+ vp->fp = SCM_FRAME_DYNAMIC_LINK (vp->fp);
+ CACHE_LOCALS ();
/* Clear stack frame. */
old_fp[0].scm = SCM_BOOL_F;
@@ -850,7 +862,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
abort ();
}
- CACHE_FP ();
+ CACHE_LOCALS ();
if (SCM_UNLIKELY (SCM_VALUESP (ret)))
/* multiple values returned to continuation */
@@ -884,7 +896,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
ret = scm_i_foreign_call (scm_inline_cons (thread, cif, pointer),
vp->sp);
- CACHE_FP ();
+ CACHE_LOCALS ();
if (SCM_UNLIKELY (SCM_VALUESP (ret)))
/* multiple values returned to continuation */
@@ -1011,9 +1023,9 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
SYNC_IP ();
dynstack = scm_dynstack_capture_all (&thread->dynstack);
vm_cont = scm_i_vm_capture_stack (vp->stack_top,
- SCM_FRAME_DYNAMIC_LINK (fp),
- SCM_FRAME_PREVIOUS_SP (fp),
- SCM_FRAME_RETURN_ADDRESS (fp),
+ SCM_FRAME_DYNAMIC_LINK (vp->fp),
+ SCM_FRAME_PREVIOUS_SP (vp->fp),
+ SCM_FRAME_RETURN_ADDRESS (vp->fp),
dynstack,
0);
/* FIXME: Seems silly to capture the registers here, when they are
@@ -1477,7 +1489,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
* If the value in A is equal? to the value in B, add OFFSET, a signed
* 24-bit number, to the current instruction pointer.
*/
- // FIXME: Should sync_ip before calling out and cache_fp before coming
+ // FIXME: Should sync_ip before calling out and cache_locals before coming
// back! Another reason to remove this opcode!
VM_DEFINE_OP (40, br_if_equal, "br-if-equal", OP2 (U8_U12_U12, B1_X7_L24))
{
@@ -1893,7 +1905,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
SYNC_IP ();
var = scm_lookup (LOCAL_REF (sym));
- CACHE_FP ();
+ CACHE_LOCALS ();
if (ip[1] & 0x1)
VM_ASSERT (VARIABLE_BOUNDP (var), vm_error_unbound (LOCAL_REF (sym)));
LOCAL_SET (dst, var);
@@ -1912,7 +1924,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
UNPACK_12_12 (op, sym, val);
SYNC_IP ();
scm_define (LOCAL_REF (sym), LOCAL_REF (val));
- CACHE_FP ();
+ CACHE_LOCALS ();
NEXT (1);
}
@@ -1972,7 +1984,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
mod = scm_the_root_module ();
var = scm_module_lookup (mod, sym);
- CACHE_FP ();
+ CACHE_LOCALS ();
if (ip[4] & 0x1)
VM_ASSERT (VARIABLE_BOUNDP (var), vm_error_unbound (sym));
@@ -2033,7 +2045,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
else
var = scm_private_lookup (SCM_CDR (modname), sym);
- CACHE_FP ();
+ CACHE_LOCALS ();
if (ip[4] & 0x1)
VM_ASSERT (VARIABLE_BOUNDP (var), vm_error_unbound (sym));
@@ -2075,7 +2087,7 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
flags = escape_only_p ? SCM_F_DYNSTACK_PROMPT_ESCAPE_ONLY : 0;
scm_dynstack_push_prompt (&thread->dynstack, flags,
LOCAL_REF (tag),
- vp->stack_top - fp,
+ vp->stack_top - vp->fp,
vp->stack_top - LOCAL_ADDRESS (proc_slot),
ip + offset,
registers);
- [Guile-commits] branch master updated (315adb6 -> f039604), Andy Wingo, 2015/10/22
- [Guile-commits] 11/12: Minor assembler cleanups, Andy Wingo, 2015/10/21
- [Guile-commits] 02/12: Fix prompt miscompilation, Andy Wingo, 2015/10/21
- [Guile-commits] 04/12: VM caches address of local 0 instead of FP,
Andy Wingo <=
- [Guile-commits] 03/12: VM stack grows downward, Andy Wingo, 2015/10/21
- [Guile-commits] 12/12: Add stack size computation to disassembler, Andy Wingo, 2015/10/21
- [Guile-commits] 05/12: Remove sp from scm_vm_cont, Andy Wingo, 2015/10/21
- [Guile-commits] 08/12: Prepare for SP-addressed locals, Andy Wingo, 2015/10/21
- [Guile-commits] 09/12: Fix boot closure wrong-num-args error, Andy Wingo, 2015/10/21
- [Guile-commits] 10/12: SP-relative local addressing, Andy Wingo, 2015/10/21
- [Guile-commits] 06/12: Rename union scm_vm_stack_element members, Andy Wingo, 2015/10/21
- [Guile-commits] 01/12: Minor VM documentation updates, Andy Wingo, 2015/10/22
- [Guile-commits] 07/12: Replace dynamic link on stack with previous frame size, Andy Wingo, 2015/10/22