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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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This is in preparation for using `Name` as a type name.
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Just like the previous change did for declaration keywords, this change uses the lexical environment to drive the lookup and dispatch of modifier parsing.
This allows us to easily add modifiers to Slang, even when they might conflict with identifiers used in user code (because the modifier names are no longer special keywords, but ordinary identifiers).
There was already some support for ideas like this with `__modifier` declarations (`ModifierDecl`) used to introduce some GLSL-specific keywords (so that they wouldn't pollute the namespace of HLSL files).
The new approach changes these to be actual `syntax` declarations (`SyntaxDecl`) with the same representation as those used to introduce declaration keywords.
Because many modifiers just introduce a single keyword that maps to a simple AST node (no further tokens/data), I modified the handling of syntax declarations so that they can take a user-data parameter, and this allows the common case ("just create an AST node of this type...") to be handled with minimal complications.
This also adds in a general-purpose string-based lookup path for AST node classes, that should support programmatic creation in more cases.
Statements are now the main case of keywords that need to be made table driven.
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The existing parser code was doing string-based matching on the lookahead token to figure out how to parse a declaration, e.g.:
```
if(lookAhead == "struct") { /* do struct thing */ }
else if(lookAhead == "interface") { /* do interface thing * }
...
```
That approach has some annoying down-sides:
- It is slower than it needs to be
- It is annoying to deal with cases where the available declaration keywords might differ by language
- Most importantly, it is not possible for us to introduce "extended" keywords that the user can make use of, but which can be ignored by the user and treated as an ordinary identifier.
That last part is important. Suppose the user wanted to have a local variable named `import`, but we also had a Slang extension that added an `import` keyword. Then a line of code like `import += 1` would lead to a failure because we'd try to parse an import declaration, even when it is obvious that the user meant their local variable. This would mean that Slang can't parse existing user code that might clash with syntax extensions. This issue is the reason why we currently have keywords like `__import`.
A traditional solution in a compiler is to map keywords to distinct token codes as part of lexing, which eliminates the first conern (performance) because now we can dispatch with `switch`. It can also aleviate the second concern if we add/remove names from the string->code mapping based on language (the rest of the parsing logic doesn't have to know about keywords being added/removed).
The solution we go for here is more aggressive.
Instead of mapping keyword names to special token codes during lexing, we instead introduce logical "syntax declarations" into the AST, which are looked up using the ordinary scoping rules of the language.
Depending on what code is imported into the scope where parsing is going on, different keywords may then be visible.
This solves our last concern, since a user-defined variable that just happens to use the same name as a keyword is now allowed to shadow the imported declaration for syntax (this is akin to, e.g., Scheme where there really aren't any "keywords").
This also opens the door to the possibility of eventually allowing user to define their own syntax (again, like Scheme).
For now I'm only using this for the declaration keywords.
With this change it should be pretty easy to also add statement keywords in the same fashion.
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Fixes #24
So far the code has used a representation for source locations that is heavy-weight, but typical of research or hobby compilers: a `struct` type containing a line number and a (heap-allocated) string.
This is actually very convenient for debugging, but it means that any data structure that might contain a source location needs careful memory management (because of those strings) and has a tendency to bloat.
The new represnetation is that a source location is just a pointer-sized integer.
In the simplest mental model, you can think of this as just counting every byte of source text that is passed in, and using those to name locations.
Finding the path and line number that corresponds to a location involves a lookup step, but we can arrange to store all the files in an array sorted by their start locations, and do a binary search.
Finding line numbers inside a file is similarly fast (one you pay a one-time cost to build an array of starting offsets for lines).
More advanced compilers like clang actually go further and create a unique range of source locations to represent a file each time it gets included, so that they can track the include stack and reproduce it in diagnostic messages.
I'm not doing anything that clever here.
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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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There were two main places where global variables were used in the Slang implementation:
1. The "standard library" code was generated as a string at run-time, and stored in a global variable so that it could be amortized across compiles.
2. The representation of types uses some globals (well, class `static` members) to store common types (e.g., `void`) and to deal with memory lifetime for things like canonicalized types.
In each case the "simple" fix is to move the relevant state into the `Session` type that controlled their lifetime already (the `Session` destructor was already cleaning up these globals to avoid leaks).
For the standard library stuff this really was easy, but for the types it required threading through the `Session` a bit carefully.
One more case that I found: there was a function-`static` variable used to generate a unique ID for files output when dumping of intermediates is enabled (this is almost strictly a debugging option).
Rather than make this counter per-session (which would lead to different sessions on different threads clobbering the same few files), I went ahead and used an atomic in this case.
Note that the remaining case I had been worried about was any function-`static` counter that might be used in generating unique names.
It turns out that right now the parser doesn't use such a counter (even in cases where it probably should), and the lowering pass already uses a counter local to the pass (again, whether or not this is a good idea).
This change should be a major step toward allowing an application to use Slang in multiple threads, so long as each thread uses a distinct `SlangSession`. The case of using a single session across multiple threads is harder to support, and will require more careful implementation work.
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- We use this to work around the fact that, e.g., `Texture2D.Load` doesn't take a sampler, but the equivalent GLSL operation `texelFetch` requires one
- Previously we tried to hide the sampler from the user, hoping that glslang would drop it and we could just ignore it, but that doesn't work
- For now we'll go ahead and explicitly show the sampler in the reflection info so that an app can react appropriately
- We also generate a unique binding for the sampler, instead of the old behavior that fixed it with `binding = 0`
- We still fix it with `set = 0`, so it might still surprise users
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- API users can use this to get "clean" output to aid with debugging Slang issues
- Also changes the prefix on intermediate files that Slang dumps, to make them easier to ignore with a regexp
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- The easy part here is treating `NV_` prefixed semantics as another case of "system-value" semantics
- Mapping the new semantics (`NV_X_RIGHT` and `NV_VIEWPORT_MASK`) to their GLSL equivalents is harder
- Instead of a single "right-eye vertex" output, GLSL defines an array of per-view positions
- Instead of a vector of masks, GLSL defines an array of per-view masks
- Another point here is that a lot of semantics that appear as `uint` in HLSL are `int` in GLSL, which can lead to conversion issues.
- The approach here is to have the lowering pass introduce a notion of assignment with "fixups," which will try to cast things as needed
- When assigning to a simple value with the "wrong" type, introduce a cast
- When assigning to an array from a vector, break out multiple assignments of individual vector/array elements
- In order to facilitate the above, I needed to add actual types to the magic expressions I introduce to represent GLSL builtin variables. These were taken by scanning the online documentation for GL, so they might not be perfect.
- Major issues with the approach in this change:
- No attempt is being made here to check that the original declaration used a type appropriate to the semantic. The assumption is that this logic only ever triggers for Slang entry points, or GLSL entry points using a Slang `struct` type for input/output (and for right now Slang code is only ever written by "understanding" developers)
- In the case of a Slang entry point, we always copy varying parameters in/out around the call to `main_`, so this approach should handle calls to functions with `out` or `in out` parameters okay, but it is *not* robust to cases where we don't want to copy in all the entry point parameters first thing (e.g., a GS), so that will have to change
- In the GLSL case (or if we revise the approach to Slang entry points), there is going to be a problem if these converted varying parameters are ever passed as arguments to `out` or `in out` parameters. In these cases we need to do more sleight-of-hand to reify a temporary variable and do the necessary copy-in/copy-out. Being able to do that logic relies on having correct information about callees, which requires having robust semantic analysis of the function body. There is only so much we can do...
- A better long-term approach would not rely on an ad-hoc "fixup" conversion during assignment, but would instead implement the GLSL builtin variables as, effectively, global "property" declarations that have both `get` and `set` accessors, and then tunnel a reference to such a property down through lowering, where it can lower to uses of the "getter" or "setter" as appropriate in context (and the result type of the getter/setter can be what we'd want/expect).
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The change is mostly about trying to make sure the compiler "fails safe" when it encounters an internal assumption that isn't met.
Most internal errors will now throw exceptions (yes, exceptions are evil, but this will work for now), and these get caught in `spCompile` so that they don't propagate to the user (they just see a message that compilation aborted due to an internal error).
Subsequent changes are going to need to work on diagnosing as many of these situations as possible, so that users can at least know what construct in their code was unexpected or unhandled by the compiler.
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Fixes #122
- In cases with an explicit mip level being specified, there was a mistake in how the argument for setting the mip level in the GLSL code was constructed that led to a parse error in GLSL
- Also, that argument is a `uint` in HLSL and an `int` in GLSL, so an explicit cast was needed
- The GLSL functions here seem to require a newer GLSL (at least higher than `420`), so I had to add in a capability for builtins to specify a required GLSL version. For now I made these ones require `450`.
- Added a test case to confirm that our lowering works (for some definition of "works")
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When lowering `buf[i]` to `texelFetch(..., i)` we need to deal with the case where the type of `b` might be `Buffer<float>` in which case we want to add a `.x` swizzle to the end of the fetch.
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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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Fixes #94
We'd been handling HLSL `Buffer` and `RWBuffer` in a one-off fashion, and that led to a lot of code duplication, and also to the issue that we weren't handling `RasterizerOrderedBuffer` at all.
This change basically folds `Buffer` in so that it is conceptually a texture type (just with a unique shape). Hopefully all the other logic still works.
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- We map `SampleCmpLevelZero` to either `textureLod` or `textureGrad` based on what the GLSL spec seems to allow
- We map `SamplerComparisonState` to `samplerShadow` (instead of just `sampler`)
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The behavior of the `linear` modifier should be the default interpolation behavior in GLSL.
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`gl_Layer` as a fragment input requires at least version 4.30 of GLSL, so we try to track that information when we see the name used.
Note that this does *not* override a user-specified `#version` line.
This required re-ordering when lowering happens relative to emitting the `#version` directive, since this code works by actually modifying the chosen profile for the entry point.
Yes, that is kind of gross and we should do something cleaner in the long term.
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Work on #105
These can occur in unchecked code (or code that had a semantic error), so we need to be able to handle them.
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Fixes #104
- Map HLSL `nointerpolation` to GLSL `flat`
- When lowering a `struct` type varying input/output, look for interpolation modifiers along the "chain" from the leaf field up to the original shader input variable (and take the first one found)
- Not sure if this is strictly needed, but it seems like a reasonable policy
- Add `flat` to varying input of integer type, with no other interpolation modifier
- Note: I do *not* do anything to ignore a manually imposed interpolation modifier that might be incorrect
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Fixes #12
- This was a latent issue, but the previous commit brought it to the front.
- As indicated in #12, I don't allocate a descriptor-table slot to the block
- Instead I allocate a `PushConstantBuffer`
- Unlike what #12 asks for, I don't use a different resource type for the contents of the block
- Pretty much all the logic is easiest if these continue to be just plain `Uniform` data
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Fixes #83
- The basic idea is that I added a bunch of more specific profile names line `glsl_vertex_430` which indicate the desired GLSL version the user wants.
- An explicit `#version` line in the code always overrides one specified by profile, though
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- This fixes the render tests, which aren't tested by the continuous integration setup
- This was broken in the commit that decided to use C-style directives all the time.
- This works for stuff that eventually passes through glslang (or at least our build of it)
- It *doensn't* work if we take the GLSL and pass it off to an OpenGL driver (which is what I do for testing)
- A longer-term fix is still required to deal with line directives properly
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When cross-compiling, we need to detect when an intrinsic is used that required non-default GLSL capabilities and emit an appropriate `#extension ... : require` line.
I'm handling this by attaching a custom modifier to declarations that require an extension in order to be callable.
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HLSL (and thus Slang) commonly puts interpolation modifiers like `sample` on the fields of `struct` types used as stage input/output, while GLSL only allows them on global-scope `in` and `out` variables (or ones in blocks).
This change emits a really hacky filtering step to skip over certain modifiers when emitting a declaration. This lets us skip interpolation-mode modifiers when outputting a struct field to GLSL.
Note: this probably gets the `in` or `out` block case wrong...
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- As long as we are always going to pass GLSL through glslang, there should be no harm in this
- Eventually we may need to re-enable the old style
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- This really just checks two basic things:
1. Was there any global variable declared with `in` and `sample`?
2. Did any code encountered during lowering referenece `gl_SampleIndex`?
- This doesn't cover what HLSL could need, nor what we would need for cross-compilation. Consider it GLSL-specific for now.
- In order to generate the information with even a reasonable chance of being accurate (not giving a ton of false positives) I tried to integrate the checks into the lowering process (so they only see code that is referenced, one hopes).
- For this to work with my testing setup, I needed to make sure that lowering is always performed, prior to emitting reflection info
- This change broke several reflection tests, because they had been using code that wouldn't actually pass the downstream compiler. I checked in fixes for those.
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- The basic idea is that during the "lowering" pass, some types (notably: aggregate types that contain resource variables) will get turned into "tuple" types, which are pseduo-types that aren't meant to survive lowering.
- An attempt to declare a variable with a tuple type expands into a tuple of declarations
- An attempt to reference such a tuple-ified variable leads to a tuple of expressions
- An attempt to extract a member from such a tuple expression will pick the appropriate sub-element
- Dereference a tuple by dereferencing the primary expression
- Expand a tuple in the argument list to a call into N arguments (by recursively flattening the tuple)
- Don't create tuple types when not generating GLSL
- Make sure to preserve the specialized type of a call expression through lowering, since emission of unchecked calls relies on that info.
- TODO: maybe the infix/prefix/postifx/select information should come in as a side-band? Should we have modifiers on expressions?
- Make sure to offset the layout for a nested field based on teh base offset of its parent variable, when generating declarations for nested fields
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The emit logic was checking for a missing decl, and then asking that same (missing) declaration for its name.
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I forgot to include a trailing space.
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This was mostly just a missing `typedef` in the Slang standard library code.
This should also cover `textureBuffer` and `samplerBuffer`.
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- Try to handle `ErrorType` gracefully when computing type layouts
- When outputting a `TypeExp`, if the type part is errorneous (or missing), try to use the expression part
- Make sure to lower the expressions side of a `TypeExp` during lowering
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- Allow a code-generation target of `NONE` in order to suppress ordinary output in test cases where we don't care about the actual output (just pass/fail result)
- Add explicit `location` layout qualifiers to intermediate vertex-to-fragment variables in GLSL test cases for rendering, to work around apparent Intel driver bugs.
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- Add GLSL mappings for more `Texture*` methods
- The annoying one here is `Texture*.Load()` because it doesn't take a sampler, but the GLSL equivalent needs one (while the SPIR-V does *not*). I've hacked this pretty seriously for now.
- Try to ensure that we add `uniform` to global declarations that need it in GLSL
- When outputting an `in` or `out` variable that might have been created from an `inout` shader parameter, filter the layout qualifiers that we output to only cover the appropriate resource kind.
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Code in Slang that is cross-compiled *might* introduce declarations that collide with language keywords that are reserved in the target.
This was previously being dealth with during final code emission, but the challenge there is that we want to allow user code that is being "rewritten" to use whatever identifiers it wants (they know better than us what is an error), and only apply renaming to our own code.
The approach here is to apply renaming during lowering - we validate each declaration to make sure its name is valid. Any expressions/types that refer to those declarations will automatically get emitted with the new name (while unchecked expressions will continue to be emitted with their existing name).
This isn't quite perfect, since we could in theory still rename a declaration in user code.
A more robust version down the line would try to determine if a declaration was nested inside code for the "rewriter."
Also note that this does *not* deal with any issues of name conflicts that might arise between modules. That would require a more complete and robust renaming pass, which seems tricky for me to pull off.
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If the user doesn't use any `import` declarations, there is no reason to parse their code at all, so having the option of falling back to `UnparsedStmt` can potentially save us some headaches down the road.
The new rule now is that if you have the "no checking" flag on, *and* the parser hasn't yet seen any `import` declarations, then it still used `UnparsedStmt` to avoid touching function bodies.
Otherwise, I go ahead and parse function bodies, and assume I can rewrite any code I can semantically understand.
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HLSL has the bad scoping behavior for `for` loops, and we need to respect that.
But, we need to have correct scoping for GLSL, and we'd like it for Slang.
We also need to ensure that `for` loops written in a "correct" language get the correct behavior when emitted as HLSL.
There was already code to handle this in the emit pass, but it was unfortunately using an `isRewrite` flag to try to tell if the HLSL behavior was wanted.
This doesn't work when the code being emitted might come from a mix of languages.
This change adds a distinct `UnscopedForStmt` syntax node type, and uses that when parsing HLSL input (bot not for other languages).
We make sure to preserve this node type through lowering, and then specialize our emit logic on this case.
With this, there are no more remaining uses of `isRewrite` in the emit logic, which is good because it didn't mean what I needed it to mean any more (since we now emit only a single module, that was merged during lowering).
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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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When emitting code it is easy to be overly defensive and emit tons of extra parentheses.
In some cases these are just annoying, and make the output more cluttered than it needs to be.
In other cases, though, being over-aggressive here can actually break things when a downstream compiler has more stringent requirements (e.g., doesn't allow a general expression for the function in a call expression, but only a particular set of atomic/postfix expressions).
This wasn't as bad when we weren't parsing function bodies in user code, but now that we *are* it becomes important to not emit bad parentheses and screw up their code. At the same time, though, we don't want to fail to output them and silently break code. A nice property today is that we preserve parentheses in the input code, so hopefully we don't ever break operator precedence.
The code already had an approach to avoid *some* parens, by tracking an "outer precedence" and only emitting parens for an expression if they were needed relative to this outer precedence. That approach doesn't handle associativity, and so it doesn't work for things like chains of postfix operators.
The new approach basically tracks *two* outer precedence levels: one on the left, and one on the right. When recursing into a sub-expression of an op (e.g., the `A` in `A + B`) on of the precdence levels for the recursive call will come from the outer environment, and the other from the operation itself (e.g., `A` has `(X, +)` as its left/right precdence, where `X` is whatever was to the left of `A + B`, while `B` gets `(+,Y)`).
One more piece of the puzzle is that an operator like `+` actually exposes *two* precedence levels: one for the left-hand side and one for the right-hand, so that if both `A` and `B` are themselves uses of `+`, `A` won't get parens, but `B` will.
Finally, when we have an un-checked application of an operator (which our AST stores as something like a function-call node), we do a little lookup step to find the corresponding operator and its precedence (while for things that actually got resolved we *know* the precedence.
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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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- Also fix a bug in `emit.cpp` where I wasn't detecting `__intrinsic` remaps that don't include `$` (this is a byproduct of changing the string index type to be unsigned; other bugs like this may be lurking)
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- I really ought to make these semantically understood attributes, which might make this logic easier
- Long-term if we start emitting SPIR-V directly, we should translte these, of course
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- Map HLSL `atan2(y,x)` to GLSL `atan(y,x)`
- Add support for `$p` escape in `__intrinsic` modifier, which allows generating GLSL texture-sampler pairs more easily
- Also added a `$o` escape to represent the base object in an OOP-style call (`obj.F(...)`)
- This isn't used in the texture functions right now, because getting the right GLSL texture type in this context is a bit thorny (the prefix depends on the generic parameter being used)
- Used the `$p` capability to add mappings for `SampleBias` and `SampleLevel`
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- This is in preparation for splitting out HLSL vs. GLSL emit as different cases.
- Along the way, I added more cases to the visitor implementation, to handle visitors with arguments
- This is getting a bit busy, though, and we might be reaching the breaking point where a more general bit of meta-magic is needed to clean things up (either going further down the ugly template route, or plugging in a more real code generation strategy)
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GLSL doesn't support `static` at all, while HLSL uses it for multiple things:
- To mark global variables that are "thread local" rather than shader parameters
- In the C/C++ style to mark `static` allocation for variables inside a function or type
The latter case needs to be handled during lowering (but isn't handled right now).
The former case can be solved just by dropping the `static` keyword.
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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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