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- Handle all statement cases explicitly (rather than falling back to the "structural recursion" mess)
- Handle back-references from child statements to their parents
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The code should now compile cleanly with warnings as errors for VS2015 with `W3`.
Most of the changes had to do with propagating a real pointer-sized integer type through code that had been using `int`.
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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 lexer was creating an `unsigned long long` value, and then the AST was storing it in an `int`.
This change makes both use a `long long`.
This is obviously still a stopgap until I can get arbitrary precisions in here.
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- Add logic to extract the value and suffix from a numeric literal
- This duplicates some of the lexing logic, but this is hard to avoid without redundant runtime work
- Note that I'm not using and stdlib string-to-number code. This should be more robust once it is working, but it is obviously error prone in the near term. The main up-sides to this are:
- We can handle binary integer literals
- We can handle hexadecimal floating-point literals without stdlib support
- We can hypothetically support digit separators, if we ever wanted
- The parser looks at the suffix characters sliced off by the lexer, and tries to pick a type to use for a literal
- It uses `NULL` if there is no suffix, to avoid some nasty order dependencies where the stdlib might need to parse a number before it has seen the definition of `int`
- Right now I only handle a few cases, so there may be bugs lurking here
- The emit logic needs to handle the fact that a literal node in the AST might have a non-default type attached.
- Right now I just quickly check for the most likely types, and emit the literal with a matching suffix. This doesn't seem robust if any source language supports a suffix for a type where a target has no corresponding suffix. In the long term some amount of casting is probably required.
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These had a typo (`Literial`), so they needed a fix eventually.
I also went ahead and made things a bit more verbose (`IntegerLiteral`, `FloatingPointLiteral`) because these names don't get used often enough for the brevity to pay off.
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This fixes up a bug in the earlier change that provided reflection for imported parameters; I'd failed to confirm that the code generation logic can handle imported parameters correctly.
The main fix was to have an `import` declaration automatically use the global-scope layout already determined, sine imported parameters will in general appear there.
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String literals can be used as part of attributes, but we lacked an actual AST representation for them.
This change adds basic parsing for string literals, as well as emit logic for them.
I also included a fix for parsing of chained right-associative operators.
To test these fixes, I've re-enabled one of the HLSL tests I disabled a while back. It would be good to go through and see how many of those we can re-enable now.
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These were being passed over by the emit logic because I didn't have tests that used them.
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If the user imports a module along more than one path, we need to make sure we don't emit the code twice.
I handle this by keeping a set of already-emitted modules.
Down the line, a more robust code generation strategy for non-"rewriter" use cases would be handling this at the per-declaration level, and this logic wouldn't really be needed.
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We now output a line directive for (nearly) every declaration, statement, and modifier, so that hopefully there will be fewer cases where a downstream error doesn't point to the correct line.
This exposes a lot of issues where we can/should clean up the simplicity of the code we emit (e.g., not output redundant parens; tracking source locations for types better).
These kinds of issues will need to be addressed in follow-on changes.
A few big ones:
- Because GLSL doesn't allow for file names in `#line` directives, we really need to expose some data that can clean up error messages (or can be used by an application to do the same) so that they know which file is which.
- We really need a command line option (and an equivalent API flag) to turn off emission of `#line` directies, so that the user can get moderately clean code as output.
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If the line number for the next token is within a small range, then go ahead and output newlines to get caught up, rather than emit a `#line` directive. This saves a small amount of clutter, and in the particular case where the number of lines is 1, it stops our current behavior of putting a directive on each line.
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When in rewriter mode, the emit logic will never see function applications inside function bodies, but it *will* see function application expressions at global scope, and some of these expressions might be unchecked.
The challenge here is that even simple math operations now show up as function calls, so we need a bit of special-case logic to detect unchecked calls and then emit them using the syntax they were written with (e.g., use infix syntax if they were written as an infix expression).
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For context: a `DeclRef` is supposed to capture both a pointer to a particualr declaration, and also any information needed to specialize that declaration for a context (e.g., generic parameter substitutions).
The existing approach had a hiearchy of specialized decl-ref types that mirrored the AST hierarchy, but that led to a lot of boilerplate where you had to recapitulate the exact same hierarchy.
The new appraoch basically treats `DeclRef<T>` as a sort of "smart pointer" in that it wraps a pointer to a `T` (the declaration), plus a side field for the specialization info, and then allows it to be cast as needed to other types (where the pointer cast would be allowed), while carrying along the side info.
To enable this, all the things that used to be member functions of declaration-reference types are now free functions that take a `DeclRef<T>` for some specific `T` as a parameter.
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This gets rid of one unecessary namespace.
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This is a large change that contains many pieces:
- Update the `cross-compile0` test to actually make use of cross compilation.
Now the `cross-compile0.hlsl` file contains both HLSL and GLSL source code, and then imports code from `cross-compile0.slang`, which provides a "library" (one function) that can be shared between both the HLSL and GLSL version of things.
- Fixed a bug in the support for backslash-escaped newlines.
- Added a new `__import` declaration type (replaces the `using` directive that was still around in a vestigial form)
An `__import` causes the compiler to look for a Slang source file (currently using the ordinary `#include` lookup logic), and then parse/check the found file as an additional module ("translation unit"), before making its declarations visible in the current scope.
- Refactored the main compilation flow to be simpler. There were the `ShaderCompiler` and `ShaderCompilerImpl` classes that weren't relaly doing anything, but added complexity to the whole workflow.
- The `render-test` application has been heavily modified to better support testing cross-compilation workflows. At the most basic level we are starting to distinguish pass-through vs. rewriter workflows, and are passing various `#define`s down to the compiler(s) to let the source code be customized as needed for each case.
Several annoying corner cases are caused here by having to support the GLSL compilation model, which really wants each entry point in its own specific translation unit, whereas we really want to keep things nicely contained in single files.
- Added support for `__intrinsic` operations to have target-specific behavior.
This allows a function to be given a different name for some specific target (so a call gets emitted as a call to that other operation).
More generally, the library writer can put together an arbitrary format string that will be used in place of expressions that call the given function, e.g.:
__intrinsic(hlsl, "$1 - $0") __intrinsic int foo(int a, int b);
Given this declaration, a call like `foo(x,y)` will code generate as `x - y` for HLSL, and as `foo(x,y)` for all other targets.
Annoying things still to be dealt with:
- The way that I'm filtering the user-provided options when passing things down to the compilation of dynamically loaded modules is a bit ad hoc. It would be good to have a systematic notion of which options will be inherited and which won't. There is also more code duplication than I'd like, so we risk having the compiler behave differently when compiling a file at the top level, vs. because of `__import`.
- Adding target-specific behavior to intrinsics is all well and good, but the current approach means we can only add this to the original declaration, which limits the ability to easily extend the set of targets.
A better approach long-term would be to add a more robust notion of target-based overload resolution (which would happen after semantic checking). Then one mechanism would be used to find the right target-specific overload to use for an operation, and then each (target-specific) definition could use a simpler attribute to intercept code-generation behavior.
Note that we might eventually need a similar notion to deal with stage- or profile-specific functions and the overloading behavior around them, so using this for intrinsics doesn't seem like a bad idea.
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