When we convert a LabeledStatement to HIR we can end up emitting "consecutive"
blocks, ie where there are two blocks such that control flow will always go from
from one block to the other, with no other way to reach the second block but
through the first. Example:
```javascript
label: {
foo();
break label;
}
bar();
```
Converts to
```
bb0:
foo()
goto bb1:
bb1:
bar();
...
```
Ideally in this case we would merge these into a single block:
* When debugging, the extra goto makes it look like there is conditional control
flow when there isn't. If the code is consecutive it's easier to understand that
if it's a single block.
* Conversion from HIR -> AST relies on consecutive code all being in a single
block, so this breaks codegen (we never visit the goto target since all gotos
are assumed to be safe to convert to a break or continue).
This PR adds a failing test case, the next PR fixes it.
Phi operands and Block predecessors currently use a `BasicBlock` reference
rather than the BlockId. This diverges from other places (like terminals) where
we use an id and not a direct object reference. Especially since blocks may get
rewritten or pruned, it's a bit cleaner to use the block id in these places.
Changes `shrink()` and `reversePostorderBlocks()` to modify the HIR in-place
rather than return a new function, for consistency with all our other passes
which mutate in-place (for performance reasons).
shrink visits all the fallthroughs even if they are unreachable so this isn't
the right place to prune unreachable blocks.
This PR moves pruning into a separate pass.
Supports computed properties (as LHS and RHS) correctly. Previously we only
handled member expressions where the property was an identifier, and would
incorrect treat `a[b]` the same as `a.b`. Now we correctly distinguish these and
convert `a[b]` as an IndexLoad and `a.b` as a PropertyLoad. Similar for
assignment, `a[b] = c` is an IndexStore. For both IndexLoad and IndexStore we
lower the property to a Place first.
Implements support for array and object de-structuring in variable declarations
and assignment expressions. Note that the code currently makes the overly
optimistic assumption that the RHS is an array or object that can be safely
indexed into. The correct representation would instead treat the RHS as possibly
iterable, but we need to consider the appropriate representation. I think it's
worth landing a first optimistic pass and we can iterate forward, this helps
make it more clear what the ideal representation would have to be and should
make a bunch of examples work. It also allows us to experiment with
representations of, and handling for, scope dependencies that involve computed
property access.
Adds new types for IndexLoad/IndexStore (renamed later in the stack to
ComputedLoad/ComputedStore) which will be used to represent computed property
access/update. The actual lowering to use these is later in the stack.
After the previous PR to change the scope dependency representation,
`Place.memberPath` is now completely unused, this PR deletes that field and all
references. Rejoice!
This is a pre-req to deleting the `Place.memberPath` field. We no longer need
memberPath in the HIR now that we have PropertyStore and PropertyLoad. However,
scope dependencies use memberPath to track the precise fields that a computation
depends upon. This PR changes scopes dependencies to use a new
`ReactiveScopeDependency` type (Place + optional path), which allows the next PR
to remove `Place.memberPath`.
Fixes codegen for chained assignment expressions. Previously each intermediate
assignment would be generated independently _in addition_ to the final chained
expression being emitted. We now emit a single chained expression, almost
exactly matching the input except for expanding from `x += 1` into `x = x + 1`.
There are two key changes:
* Ensuring that assignment expressions always generate an lvalue, which is
necessary for alias analysis to kick in, since it relies on the effect of the
lvalue to know where to look for aliasing.
* The above makes codegen think the entire assignment expression value is a
temporary that can be emitted later, but that isn't true. The new
PruneTemporaryLValue pass nulls out lvalues that are never read later, ensuring
that codegen can eagerly emit the value instead of saving it as a temporary.
Converts assignment expressions where the lvalue is a MemberExpression to use
PropertyStore, rather than creating an lvalue with a member path. The net effect
is that lvalue will always have a null member path.
There are two main cases:
* `x.y = <value>`. We lower <value> to a Place, lower the object of the member
expression to a place (`object)` create a temporary Place for the result of the
assignment, and then create a `PropertyStore <object>, "<property>", <value>`.
* `x.y += <value>` (and similar update-in-place operands). We extract the object
of the member expression, read the current value via a PropertyLoad, compute the
updated value, and store it back with a PropertyStore (each of these goes into
its own temporary).
Adds a `InstructionValue::PropertyStore` variant and the minimal necessary
handling across the passes to get things to compile. Lowering is in the next PR.
…-realsies"
This reverts commit 3c8700cbc7502e56cca8d4bb77a08e1ee747c166.
I'm not sure how this happened but I accidentally hit up + enter on a previous
`ghstack land` command for a different stack and it landed this one.
Infuriating.
For unknown reasons I didn't have the energy to dig into, some Babel Error
objects can't be written to so despite formatting the error message, the
original one would still be used. To get around this I'm just constructing a
fake object with a `name` and `message` so the correctly formatted messages are
used.
This is an incremental step to removing `Place.memberPath`. This PR changes how
we handle MemberExpressions in rvalue position, converting to a new
`PropertyLoad` InstructionValue variant. Example:
```
let x = a.b;
x.y = b.c;
=>
Const tmp1 = PropertyLoad a, 'b';
Const x = Place tmp1;
Const tmp2 = PropertyLoad b, 'c';
Reassign x.y = tmp2
```
That we already recently made a chance to ensure that _if_ the lvalue is a
member expression, that we convert the RHS to a Place. So although `x.y = b.c`
could technically be lowered to a single instruction (with the`b.c` as a
PropertyLoad), we force this to a temporary to ensure that we can independently
memoize the RHS value.
The net result is that the following combinations are possible:
* `x = y`, lvalue identifier, rvalue identifier
* `x.y = y` lvalue member path, rvalue identifier
* `x = y.z` lvalue identifier, rvalue property load
As noted above, `x.y = a.b` no longer occurs (and there's an invariant for this
in one of the passes).
A follow-up PR will add a PropertyStore instruction so that we can remove member
paths in lvalue position too.
@josephsavona had the intuition that we were picking the wrong root in the
previous infinite loop test case, so the fix for this is to force a root to
always be picked. This works because `find` implements path compression (if a <-
b and b <- c, then we can just point a <- c to "flatten" the tree which makes
subsequent `find` operations more efficient since we don't have to follow the
ancestor chain each time), so we're forcing all those unions to pick one parent.
From some googling it looks like the traditional way to implement union is to
call `find` so this should be the "right" way to fix it (?).
I'm also adding a basic unit test for DisjointSet, I think we could revisit
later and see if property testing is worth it but for now I mainly wanted to
capture the regression test as a unit test.
Discovered this by accident modifying Joe's playground example. This seemed to
be triggered in inferReactiveScopeVariables when iterating over the DisjointSet
of scopeIdentifiers. In particular this test case contains a cycle and
DisjointSet.find would never terminate.
The github action was exceeding maximum allowed memory size because we were no
longer grouping messages correctly prior to formatting them in the script. I
think these were introduced when we integrated the Babel plugin into the
preprocessor. This PR strips out filenames from the message so they can be
grouped together again. Also added some light comments
Test plan: manually ran `scripts/test262.sh` and verified that the JSON was
grouped together correctly
Previously we weren't ever clearing the `dist` directory so there were likely
some vestigial files left over from previous builds that might have confused the
import path. This commit fixes the import path and also deletes the `dist`
directory on every build to ensure a clean slate.
Given that our type inference needs to be very conservative, there's not a lot
of benefit to having such fine grained type inference.
In the future, we can use type information from flow/ts for inference.
For now, we've decided to punt on super fine grained aliasing of fields (ie,
mutating x.y shouldn't mutate x.z or it's aliases).
This PR removes the code that tracks the aliases of each field. We can re-add
this when we revisit this functionality.
For the rest of the field aliasing, most of it has been replaced by
InferAliasForStores.
Splits handling of simple assignment updates (`=`) from update-assignments (`+=`
etc). This unblocks starting to support destructuring for the simple case in the
subsequent PR.
The test262 preprocessor was correctly running forget against all the functions
in each test file, but it was incorrectly transforming the file contents
overall. Previously we swapped the contents of the file for the transformed
output of the last function, now we use the babel plugin to rewrite functions in
place and keep the rest of the file intact.
Of course, the tests that failed before still fail. But when we fix them the
tests will work now.
Addressed a TODO from the previous PR. When we enter SSA form, when we rewrite
variable reassignments we currently change the identifier but leave the kind of
the lvalue alone; technically we should convert from Reassign to Const. After
doing that, it's easier to correctly update when we leave SSA form, we can
convert just a subset back into let/reassign (but leave most things alone as
const).
Reorders LeaveSSA so that it runs before we begin evaluating reactive scopes.
Note that reactive scopes must span the full construction of each variable — for
variables with a phi, this must span the declaration and all assignments of the
phi operands. And that's exactly what the new LeaveSSA does! LeaveSSA removes
phi nodes and ensure that all versions of a variable which flow into a phi have
been assigned a single canonical identifier (with an appropriate mutable range).
This PR includes this and some related changes:
* Reorders the pass
* Changes hir-test to print the final HIR, eg just prior to codegen
* Teaches LeaveSSA to update the mutable range of the canonical identifiers it
assigns, based on the min/max of the variables assigned.
Rather than special casing for field stores, look for Effect.Store to alias
fields.
In the future, this will be extended to other constructs like Array#push.
Effect.Store is exactly like Effect.Mutate, the only difference is that Store
aliases one into a another value.
There is no practical difference between Effect.Mutate and Effect.Store
currently.
Assignment expressions to a member path are a special case because they're the
only place where a value isn't assigned to a (possibly temporary) variable,
which is our unit of memoization. #901 demonstrated how this can lead to values
that can't be independently memoized:
```javascript
const x = {a: a}
x.y = [b, c]; // array recomputed w `x`, even if only `a` changed
```
This PR ensures that assignment expressions where the LHS is a member path lower
the RHS to a Place. That means the above example is handled as if you wrote:
```javascript
const x = {a: a};
const tmp1 = [b, c];
x.y = tmp1;
```
And we independently memoize the temporary.
Joe Savona
Sathya Gunasekaran
lauren