So far it's unclear how to do this in a series of small commits. Still
nibbling around the edges. In this commit we standardize some terminology:
The length of an array or stream is denominated in the high-level elements.
The _size_ is denominated in bytes.
The thing we encode into the type is always the size, not the length.
There's still an open question of what to do about the Mu `length` operator.
I'd like to modify it to provide the length. Currently it provides the
size. If I can't fix that I'll rename it.
At the SubX level we have to put up with null-terminated kernel strings
for commandline args. But so far we haven't done much with them. Rather
than try to support them we'll just convert them transparently to standard
length-prefixed strings.
In the process I realized that it's not quite right to treat the combination
of argc and argv as an array of kernel strings. Argc counts the number
of elements, whereas the length of an array is usually denominated in bytes.
If indexing into a type with power-of-2-sized elements we can access them
in one instruction:
x/reg1: (addr int) <- index A/reg2: (addr array int), idx/reg3: int
This translates to a single instruction because x86 instructions support
an addressing mode with left-shifts.
For non-powers-of-2, however, we need a multiply. To keep things type-safe,
it is performed like this:
x/reg1: (offset T) <- compute-offset A: (addr array T), idx: int
y/reg2: (addr T) <- index A, x
An offset is just an int that is guaranteed to be a multiple of size-of(T).
Offsets can only be used in index instructions, and the types will eventually
be required to line up.
In the process, I have to expand Input-size because mu.subx is growing
big.
Anytime we create a slice, the first check tends to be whether it's empty.
If we handle ill-formed slices here where start > end, that provides a
measure of safety.
In the Mu translator (mu.subx) we often check for a trailing ':' or ','
and decrement slice->end to ignore it. But that could conceivably yield
ill-formed slices if the slice started out empty. Now we make sure we never
operate on such ill-formed slices.
Layers 0-89 are used in self-hosting SubX.
Layers 90-99 are not needed for self-hosting SubX, and therefore could
use transitional levels of syntax sugar.
Layers 100 and up use all SubX syntax sugar.
A couple more primitives now working. In the process I ran into an issue
with some buffer filling up when running ntranslate. Isolating it to survey.subx
was straightforward, but --trace ran out of RAM, and --trace --dump ran
out of (7GB of) disk. In the end what helped was just repeatedly inserting
exits at different points, and I realized there was a magic number that
hadn't been turned into a named constant.
Support binary operations with reg/mem and reg operands.
Everything is passing. However, the self-hosting translator now generates
some discrepancies compared to the C++ translator :(
Move stack operations to a layer of their own.
It was some short-term pain to take out the syntax sugar from it, but we
need access to this layer from braces, which can't depend on sugar since
it's part of sugar. Just simpler to keep one clear line and not have to
build sometimes with some sugar but not others.
This undoes 5672 in favor of a new plan:
Layers 000 - 099 are for running without syntax sugar. We use them for
building syntax-sugar passes.
Layers 100 and up are for running with all syntax sugar.
The layers are arranged in approximate order so more phases rely on earlier
layers than later ones.
I plan to not use intermediate syntax sugar (just sigils without calls,
or sigils and calls without braces) anywhere except in the specific passes
implementing them.
Right now we always build the library before any apps.
Apps are where our syntax sugar translators (sigils, calls, braces) live.
So we can't use sugar in the standard library.
New idea: move all code for SubX phases into the top-level.
Perhaps we should also just build a single file rather than pipeline stages.
But for now we'll build each phase by building up to some specific layer.
This will simplify test_apps and move lots of one-off logic to a more standard
form in test_layers.
I'm also going to reorg existing layers so that we introduce each phase
at a point where it mostly only gets the helpers it needs.
This commit itself is just cleaning up some common strings. Using explicit
names for them streamlines binaries a bit.
Probably not needed for desugar; I'm just working through what we may
replace the calls to 'get-slice' with if and when we decide to start
focusing error messages and so writing tests for them.
Kartik Agaram