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Minor VM documentation updates

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* doc/ref/vm.texi (Why a VM?, Variables and the VM): Minor updates.
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Andy Wingo 2015-09-18 10:43:06 +02:00
parent 315adb6347
commit a0a8741608
1 changed files with 9 additions and 7 deletions
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@ -80,11 +80,12 @@ but it is not normally used at runtime.)
The upside of implementing the interpreter in Scheme is that we preserve The upside of implementing the interpreter in Scheme is that we preserve
tail calls and multiple-value handling between interpreted and compiled tail calls and multiple-value handling between interpreted and compiled
code. The downside is that the interpreter in Guile 2.2 is still slower code. The downside is that the interpreter in Guile 2.2 is still about
than the interpreter in 1.8. We hope the that the compiler's speed makes twice as slow as the interpreter in 1.8. Since Scheme users are mostly
up for the loss. In any case, once we have native compilation for running compiled code, the compiler's speed more than makes up for the
Scheme code, we expect the new self-hosted interpreter to beat the old loss. In any case, once we have native compilation for Scheme code, we
hand-tuned C implementation. expect the self-hosted interpreter to handily beat the old hand-tuned C
implementation.
Also note that this decision to implement a bytecode compiler does not Also note that this decision to implement a bytecode compiler does not
preclude native compilation. We can compile from bytecode to native preclude native compilation. We can compile from bytecode to native
@ -213,8 +214,9 @@ variables are allocated in ``boxes''---actually, in variable cells.
variables are indirected through the boxes. variables are indirected through the boxes.
Thus perhaps counterintuitively, what would seem ``closer to the Thus perhaps counterintuitively, what would seem ``closer to the
metal'', viz @code{set!}, actually forces an extra memory allocation metal'', viz @code{set!}, actually forces an extra memory allocation and
and indirection. indirection. Sometimes Guile's optimizer can remove this allocation,
but not always.
Going back to our example, @code{b} may be allocated on the stack, as Going back to our example, @code{b} may be allocated on the stack, as
it is never mutated. it is never mutated.