compiler: frame-eliminating optimization.

This optimization identifies let blocks whose variables are
not captured by closures. The variables are relocated to
registers and the frame M N ... end reg wrapping is removed.

* parser.c (read_file_common): Load version 6 files.
We remain backwards-compatible.

* share/txr/stdlib/compiler.tl (var-spy, capture-var-spy): New
structure types.
(struct compiler): New slot, var-spies.
(with-var-spy): New macro.
(compiler (alloc-new-treg, unalloc-reg-count, push-var-spy,
pop-var-spy)): New methods.
(compiler (comp-atom, compt-setq, comp-list-setq,
comp-lisp1-value)): Inform the spies in the spy notification
stack about assignments and accesses.
(compiler eliminate-frame): New method.
(compiler comp-let): Use spies to determine which variables
from this frame are captured, and if none are, then use
eliminate-frame to rename all the variables to t-registers and
drop the frame setup/teardown.
(compiler comp-lambda): Set up a capture-var-spy which
intercepts accesses and assignments within a lambda, and
informs other spies about the captures.
(%tlo-ver%): Bump compiled file version to to (6 0), because
of some behavioral changes necessary in the VM. We might
revert this if the issues are solved differently.

* vm.c (vm_getz): Do not null out T registers.
(vm_execute_toplevel, vm_execute_closure): Use zalloca to
allocate the register part of the frame, so T registers are
initialized to nil.

1 files changed, 4 insertions, 4 deletions

diff --git a/vm.c b/vm.c
index f53962f3..8e7433f0 100644
--- a/vm.c
+++ b/vm.c
@@ -359,7 +359,7 @@ INLINE val vm_getz(struct vm_env *dspl, unsigned ref)
 {
   unsigned lev = vm_lev(ref);
   val *addr = &dspl[lev].mem[vm_idx(ref)];
-  return (lev == 0) ? z(*addr) : *addr;
+  return *addr;
 }
 
 INLINE val vm_sm_get(struct vm_env *dspl, unsigned ref)
@@ -1124,7 +1124,7 @@ val vm_execute_toplevel(val desc)
   val self = lit("vm-execute-toplevel");
   struct vm_desc *vd = vm_desc_struct(self, desc);
   struct vm vm;
-  val *frame = coerce(val *, alloca(sizeof *frame * vd->frsz));
+  val *frame = coerce(val *, zalloca(sizeof *frame * vd->frsz));
   struct vm_env *dspl = coerce(struct vm_env *, frame + vd->nreg);
 
   vm_reset(&vm, vd, dspl, 1, 0);
@@ -1152,7 +1152,7 @@ val vm_execute_closure(val fun, struct args *args)
   struct vm_desc *vd = vm_desc_struct(self, desc);
   struct vm_closure *vc = coerce(struct vm_closure *, closure->co.handle);
   struct vm vm;
-  val *frame = coerce(val *, alloca(sizeof *frame * vd->frsz));
+  val *frame = coerce(val *, zalloca(sizeof *frame * vd->frsz));
   struct vm_env *dspl = coerce(struct vm_env *, frame + vd->nreg);
   val vargs = if3(variadic, args_get_rest(args, fixparam), nil);
   cnum ix = 0;
@@ -1214,7 +1214,7 @@ val vm_execute_closure(val fun, struct args *args)
   struct vm_desc *vd = vm_desc_struct(self, desc);                           \
   struct vm_closure *vc = coerce(struct vm_closure *, closure->co.handle);   \
   struct vm vm;                                                              \
-  val *frame = coerce(val *, alloca(sizeof *frame * vd->frsz));              \
+  val *frame = coerce(val *, zalloca(sizeof *frame * vd->frsz));             \
   struct vm_env *dspl = coerce(struct vm_env *, frame + vd->nreg);           \
   vm_reset(&vm, vd, dspl, vc->nlvl - 1, vc->ip);                             \
   vm.dspl = coerce(struct vm_env *, frame + vd->nreg);                       \