Remove the type canonicalization mechanism and instead rely on constant
canonicalization to deduplicate types.
Rename the `Canonicalize*Type` functions to reflect that they're no
longer performing canonicalization. Switch code that creates types due
to semantic checking, rather than due to source syntax, to directly
create type constants through evaluation rather than creating an
instruction and evaluating it to produce a separate constant
representation.
The mapping from `const (const T)` that was previously performed by type
canonicalization is now implemented in expression evaluation instead.
The value `<error>` is now treated as a constant value, with a special
property that an instruction involving `<error>` that could possibly be
constant evaluates to `<error>`. This helps avoid producing follow-on
errors when an error occurs as a subexpression of an expression, such as
a type, that is intended to be constant.
Rather than producing multiple constants with the same value, fold all
instances of a given constant to the same constant instruction.
A future PR will use this to replace the current type canonicalization
system.
The parse nodes are still tracked as part of the same value store
interface in order to ensure parity, but they're split out from Inst
itself in order to reduce the size of Inst -- the expectation is that
they don't need to be passed around quite as much.
This change doesn't actually reduce the passing very much, although
there are hints of it: AddInstAndPush doesn't typically need a separate
parse node from the one on the Inst itself, for example. In a couple
spots I changed code to rely a little more on the InstId until the
ParseNode is needed, but it's very low hanging fruit where done. I think
convert could do more to not eagerly fetch the parse node before its
use, but more cleanup felt it would be easier to handle separately. I'm
currently viewing this as making such cleanup _possible_ rather than
executing on it up-front.
But also, I want to make sure there's a consensus to head in this
direction before pulling the trigger. We speculated that this would
result in the parse node being passed around less, and I do think that's
the case, although it's a bit fuzzy in the change.
---------
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
This is accomplished by tracking an extra bit on the ID we store in the
constant values table, and propagating that from subexpressions to the
enclosing expression. This extra bit is not yet computed correctly for
types; that will be addressed in later PRs.
---------
Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
Form a side table with constant values for each instruction. Evaluation
is only supported for a few very simple kinds of instruction for now.
This is not observable outside of the SemIR output, because nothing
depends on expressions having a constant value phase yet.
josh11b
Richard Smith
Jon Ross-PerkinsandRichard Smith
