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This is the first step towards supporting traditional object-oriented method definitions; the second step will be to allow `this` expressions to be implicit.
- Add a test case using explicit `this`, and expected output
- Update parsing logic for expressions so that it handled identifiers similarly to the declaration and statement logic: first try to parse using a syntax declaration looked up in the curent scope, and otherwise fall back to the ordinary `VarExpr` case.
* As long as I'm making that change: switch `true` and `false` to be parsed via the callback mechanism rather than be special-cased.
* This change will also help out if we ever wanted to add `super`/`base` expressions, `new`, `sizeof`/`alignof` or any other expression keywords.
- Add a `ThisExpr` node and register a parser callback for it.
- Add semantic checks for `ThisExpr`: basically just look upwards through scopes until we find either an aggregate type declaration or an `extension` declaration, and then use that as the type of the expression.
- TODO: eventually we need to guard against a `this` expression inside of a `static` member.
- The IR generation logic already handled creation of `this` parameters in function signatures; the missing piece was to register the appropriate parameter in the context, so that we can use it as the lowering of a `this` expression.
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The main interesting change here is around support for lowering of calls to "subscript" operations (what a C++ programmer would think of as `operator[]`).
An important infrastructure change here was to add an explicit AST-node representation for a "static member expression" which we use whenever a member is looked up in a type as opposed to a value. The implementation of this probably isn't robust yet, but it turns out to be important to be able to tell such cases apart.
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- Previously, there were a variety of rules in `check.cpp` to pick the conversion cost for various cases involving scalar, vector, and matrix types.
- The main problem of the previous approach is that any lowering pass would need to convert an arbitrary "type cast" node into the right low-level operation(s).
- The new approach is that a type conversion (implicit or explicit) always resolves as a call to a constructor/initializer for the destination type. This means that the existing rules around marking operations as builtins should work for lowering.
- The support this, the checking logic needs to perform lookup of intializers/constructors when asked to perform conversion between types. It does this by re-using the existing logic for lookup and overload resolution if/when a type was applied in an ordinary context.
- Next, we define a modifier that can be attached to constructors/initializers to mark them as suitable for implicit conversion, and associate them with the correct cost to be used when doing overload comparisons.
- We add the modifier to all the scalar-to-scalar cases in the stdlib, using the logic that previously existed in semantic checking.
- Next we add cases for general vector-to-scalar conversions that also convert type, using the same cost computation as above.
- This probably misses various cases, but at this point they can hopefully be added just in the stdlib.
- One gotcha here is that in lowering, we need to make sure to lower any kind of call expression to another call expression of the same AST node class, so that we don't lose information on what casts were implicit/hidden in teh source-to-source case.
Two notes for potential longer-term changes:
1. There is still some duplication between the type conversion declarations here and the "join" logic for types used for generic arguments. Ideally we'd eventually clean up the "join" logic to be based on convertability, but that isn't a high priority right now, as long as joins continue to pick the right type.
2. It is a bit gross to have to declare all the N^2 conversions for vector/matrix types to duplicate the cases for scalars. For the simple scalar-to-vector case, we might try to support multiple conversion "steps" where both a scalar-to-scalar and a scalar-to-vector step can be allowed (this could be tagged on the modifiers already introduced). That simple option doesn't scale to vector-to-vector element type conversions, though, where you'd really want to make it a generic with a constraint like:
vector<T,N> init<U>(vector<U,N> value) where T : ConvertibleFrom<U>;
Here the `ConvertibleFrom<U>` interface expresses the fact that a conforming type has an initializer that takes a `U`. What doesn't appear in this context is any notion of conversion costs. We'd need some kind of system for computing the conversion cost of the vector conversion from the cost of the `T` to `U` converion.
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Fixes #23
Up to this point, the compiler has used the ordinary `String` type to represent declaration names, which means a bunch of lookup structures throughout the compiler were string-to-whatever maps, which can reduce efficiency.
It also means that things like the `Token` type end up carying a `String` by value and paying for things like reference-counting.
This change adds a `Name` type that is used to represent names of variables, types, macros, etc.
Names are cached and unique'd globally for a session, and the string-to-name mapping gets done during lexing.
From that point on, most mapping is from pointers, which should make all the various table lookups faster.
More importantly (possibly), this brings us one step closer to being able to pool-allocate the AST nodes.
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- `ExpressionSyntaxNode` becomes `Expr`
- `StatementSyntaxNode` becomes `Stmt`
- `StructSyntaxNode` becomes `StructDecl`
- `ProgramSyntaxNode` becomes `ModuleDecl`
- `ExpressionType` becomes `Type`
- Existing fields names `Type` become `type`
- There might be some collateral damage here if there were, e.g., `enum`s named `Type`, but I can live with that for now and fix those up as a I see them
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GLSL technically supports varying (`in`, `out`) parameters of `struct` type, but there are some annoying constraints (not allowed for VS input), and it doesn't work with how an HLSL user would usually put "system-value" inputs/outputs into a `struct` together with ordinary inputs/outputs.
To work around this, this change adds support for using an imported Slang `struct` type for an `in` or `out` parameter, in which case it will (1) be scalarized and (2) will have system-value semantics mapped appropriately, just as for an entry-point parameter when cross-compiling an HLSL-style `main()`.
Changes:
- Add a notion of a `VaryingTupleExpr` and `VaryingTupleVarDecl`, similar to those for the resources-in-structs case
- Trigger use of these when we have a global-scope varying in/out using an imported `struct` type
- Also use these in the cross-compilation case for ordinary varying input/output (since this approach seems like it should be more general, and can hopefully handle stuff like GS input/output some day)
- When generating parameter binding information, special case global-scope input/output, and treat it the same as entry-point-parameter input/output
- Revamp how used resource ranges are computed so that we can eventually make this specific to an entry point
- Actually implement first signs of life for `maybeMoveTemp` so that assignments to the tuple-ified outputs will work better
- Add first test case that actually seems to work
- Add diagnostics for conflicting explicit bindings on a parameter
- Add diagnostic for different parameters with overlapping bindings
- Make global-scope varying input/output use a tracking data structure specific to the translation unit for computing locations (so that they are independent of other TUs)
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The old approach used an `isRewriter` flag in the emit logic, but I kind of need that flag to go away.
Instead, I now how the semantic checking pass detect whether an implicitly-generated type cast is in rewriter code, and if so it uses the new `HiddenImplicitCastExpr` AST node.
The emit logic then looks for that specific node and eliminates it.
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This is in anticipation of needing to have more complete knowledge to be able to handle user code that `import`s library functionality.
The big picture of this change is just to remove the `UnparsedStmt` class that was used to hold the bodies of user functions as opaque token streams, and thus to let the full parser and compiler loose on that code. That is the easy part, of course, and the hard part is all the fixes that this requires in the rest of the compielr to make this even remotely work.
Subsequent commit address a lot of other issues, so this particular commit mostly represents work-in-progress.
One detail is that this change puts a conditional around nearly every diagnostic message in `check.cpp` to suppress thing when in rewriter mode.
I have yet to check how that works out if there are errors in anything we actually need to understand for the purposes of generating reflection data.
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- The big change here is the introduction of a "lowering" pass that takes an input AST from the semantic checker, and produces an output AST suitable for emitting. The intention is that he lowering pass is responsible for:
- Stripping out unused code (when we have enough information to do so), by only outputting declarations that are transitively references from an entry point
- When cross-compiling to GLSL, generating a suitable `void main()` entry point to wrap the user-written entry-point function
- (Eventually) legalizing types in the program, by scalarizing aggregate types that mix uniform and resource types
- (Eventually) instantiating generic declarations so that the resulting code only deals with fully specialized declarations
- (Eventually) de-sugaring OOP constructs into basic "structs and functions" form
- (Eventually) instantiating code that depends on interface types at the concrete types chosen
- It is clear that there is still a lot of work to be done there, to this change is really about getting infrastructure in place without breaking the existing test cases.
- One cleanup here is that we get rid of the idea of whole-translation-unit output, since that was specific to HLSL output, and there is really no strong reason for keeping it. Users should now just ask for the output for each entry point that they wanted to generate.
- The biggest source of complexity for the lowering process is that it needs to produce the same AST structure as the input, to deal with the complexity of the rewriter case. That is, we need the output to be able to reproduce the input exactly in the case where we are rewriting and nothing needs to change, so the output format needs at least the degrees of freedom of the input.
- As a result, we end up having to distinguish "rewriter" and "full" modes in both lowering and code-emit steps, so that we can react appropriately.
- Generating a GLSL `main()` also adds a lot of complexity. Right now I'm using the simplest approach, where we always output the Slang/HLSL entry point as an ordinary function (as written) and then emit a simple GLSL `main()` to call it. I generate globals for all the shader inputs/outputs (these need to be scalarized and have explicit `location`s attached), and then collect these into the `struct` types of the original parameters as needed.
- This approach will start to have some major down-sides once we have to deal with "arrayed" input/output
- A long-term question here is how to replace entry-point parameter types with scalarized and/or "transposed" versions, while still letting the original code work as written (including copying those inputs to temporary arrays)
- Split `BlockStatementSyntaxNode` into:
- `BlockStmt` which just provides a scope around a `body` statement
- `SeqStmt` which just allows multiple statements to be treated as one
- Change how we emit `for` loops, to deal with the case where the initialization part might expand into multiple statements
- Basically `for(A;B;C) {D}` becomes `{A; for(;B;C) {D}}`, so we can handle arbitrary statements for `A`
- As an additional wrinkle, when we are rewriting HLSL, we just generate `A; for(;B;C) {D}` to deal with the broken scoping there
- This change is needed because the lowering pass was sometimes expanding the original initialization statement `A` into a block `{A}`. Certainly if it declared multiple variables we'd need to handle it, and this seemed the easiest way
- A more significant challenge for lowering would come if/when we ever wanted to support true short-circuiting behavior for `&&` and `||`
- For right now I'm not changing the behavior of the "rewriter" mode, so we still have `UnparsedStmt` instances being generated, but it is clear that eventually we need to parse *all* input, even if we can't type-check 100% of it. This is required so that we can rewrite user code that might refer to a shader input with interface type.
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- The big change here is that all the definitions for syntax-node classes have been macro-ized, to that we can do light metaprogramming over them
- The use of macros for this has big down-sides, but I'm not quite ready to do anything more heavy-weight right now
- The macro-ized definitions can be included multiple times, to generate different declarations/code as needed
- The first example of using this meta-programming facility is a new visitor system
- The actual visitor base classes and the dispatch logic are all generated from the meta-files
- There was only one visitor left in the code: the semantics checker, so that was ported to the new system.
- All current test cases pass, so *of course* that means all is well.
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