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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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Make source location lightweight
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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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Major naming overhaul:
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Fix use of "pseudo-syntax" in current lowering pass
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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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The so-called "lowering" pass (really a kind of AST-to-AST legalization pass right now) needs to handle some basic scalarization of structured types, and it does this by inventing what I call "pseuo-expressions" and "pseudo-declarations."
For example, there is a pseudo-expression node type that represents a tuple of N other expressions, and certain operations act element-wise over such tuples.
The problem was that the implementation introduced these out-of-band expression/declaration types into the existing AST hierarchy which led to a dilemma:
- If these new AST nodes were declared like all the others (and integrated into the visitor dispatch approach, etc.) then every pass would need to deal with them even though they are meant to be a transient implementation detail of this one pass
- But if the new nodes *aren't* declared like the others, then they can't meaningfully interact with visitor dispatch, and will just crash the compiler if they somehow "leak" through to latter passes. And because they are just ordinary AST nodes from a C++ type-system perspective, such leaking is entirely possible (if not probable)
Hopefully that setup helps make the solution clear: instead of having the "lowering" pass map an expression to an expression, it needs to map an expression to a new data type (here called `LoweredExpr`) that can wrap *either* an ordinary expression (the common case) or one of the new out-of-band values. Any code that accepts a `LoweredExpr` needs to handle all the cases, or explicitly decide that it can't/won't deal with anything other than ordinary expressions.
Most of the code changes are straightforward at that point, although the whole "lowering" approach is a bit fiddly right now, so gertting the tests passing took a bit of attention. I'm not sure our test coverage of all this code is great, so I wouldn't be surprised if some failures are lurking still.
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Remove uses of global variables
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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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Typo fix.
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Update documentation.
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- Update readme to fill out some of the `TODO` sections
- Add an API user's guide that gives the basics of linking against Slang and using it to compile and reflect shaders
- Add a bit of usage info for the command-line `slangc` program
- Add an overview of the Slang language as it stands today
- Add an initial FAQ, mostly to help answer the "why should I use this?" question
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Add Code of Conduct
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Add a `-o` option to command-line `slangc`
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Fixes #11
- This adds a `-o` command-line option for specifying an output file.
- The code tries to be a bit smart, to glean an output format from a file extension, and also to associate multiple `-o` options with multiple `-entry` options if needed.
- There is a restriction that all the output files need to agree on the code generation target. This is reasonable for now, but might be something to lift eventualy
- There is a restriction that only one output file is allowed per entry point
- Together with the previous item this means you can't output both a `.spv` and a `.spv.asm` in one pass, even though both should be possible
- There is currently a restriction that output paths only apply to entry points
- This means there is no way to output reflection JSON to a file with `-o` (but that is mostly just a debugging feature for now)
- This also means we don't support any "container" formats that can encapsulate multiple compiled entry points
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Fixup for the glslang bug workaround
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There was a bug where the intialization expression for a variable was being lowered after the declaration was added to the output code, so that any sub-expressions that get hoisted out actually get computed *after* the original variable. This obviously led to downstream compilation failure.
I've updated the test case to stress this scenario.
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Work around glslang issue 988
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The basic bug there is that if you have a member of `struct` type in a `uniform` block and then pass a reference to that member directly to a call:
```
struct Foo { vec4 bar; };
uniform U { Foo foo; };
void main() { doSomething(foo); }
```
then glslang generates invalid SPIR-V which seems to cause an issue for some drivers.
This change works around the problem by detecting cases where an argument to a function call is a reference to `uniform` block member (of `struct` type) and then rewrites the code to move that value to a temporary before the call.
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Make the "hack" sampler explicit for now
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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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Map HLSL `frac()` to GLSL `fract()`
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Don't add `flat` qualifier to integer fragment output
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Fixes #133
We already had logic to skip adding `flat` to a vertex input, and this just extends it to not adding `flat` to a fragment output.
Note that explicit qualifiers in the input HLSL/Slang will still be carried through to the output, so it is still possible for a Slang user to shoot themself in the foot with interpolation qualifiers.
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Add an API option to control emission of `#line` directives
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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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Require extension when using `gl_Layer` in VS
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The requirements for using `gl_Layer` differ by stage, and so we need to pick an appropriate GL version based on the target stage, and then also require a specific extension for anything other than geometry or fragment.
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Translate NV single-pass stereo extension from Slang to GLSL
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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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Try to improve handling of failures during compilation
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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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Use AppVeyor to deploy to GitHub Releases
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- Change naming convention for output directory
- `windows-x86` and `windows-x64`
- Lower-case for `debug`, `release`
- Test script needed to be patched up for this
- Add packaging and deployment logic to AppVeyor CI script
- Trigger deployment on new tag
- Compute a release version based on Git tag name (`vX.Y.Z` becomes `X.Y.Z`)
- Fallback to hash in case tag isn't available (it should always be)
- Bundle files into a few artifacts (binary package + source package)
- Set up to push those files into existing GitHub tag/release
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Build a dynamic library for Slang
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- Change the `slang` project from a static library to a dynamic one
- Add some details around `slang.h` to make sure DLL export stuff is working
- Make the `slangc` executable use the dynamic library
- Rename the `glslang` sub-project to `slang-glslang` and move it into the main source hierarchy
- This reflects the fact that it isn't a stand-alone tool, and isn't in any way a standard binary of glslang, but rather just an artifact of how Slang uses glslang
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Fix up translation of `GetDimensions()`
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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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Fixes for how parameter block names are set up.
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We generate implicit names for global-scope parameter blocks (including HLSL `cbuffer`s, since the "name" the user sees is really just for reflection purposes), but this had a few problems:
- We used the generated names for parameter-binding purposes
- Except for a GLSL block with an explicit name, in which case we'd use the internal name and not the reflection name for matching
- The generated named didn't match between GLSL and HLSL/Slang declarations
This change tries to fix both of these issues. I changed the name generation to try to make it identical between HLSL and GLSL (to the extent we can control it), just in case. But then I also went and changed the parameter-binding-generation logic to use the *reflection* name instead of the internal name when deciding if things are the "same" parameter.
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Gaussian blur fixes
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Add a compile-time loop construct to Slang
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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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- This isn't going to work for writable buffers, and certainly not for writes
- As it exists right now, this shows a flaw in how I'm handling texture-type results on fetches
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The basic syntax is:
$for(i in Range(0,99))
{
/* stuff goes here */
}
Note that the exact form is very restrictive. All that you are allowed to change is `i`, `0`, `99` or `/* stuff goes here */`.
As a tiny bit of syntax sugar, the following should work:
$for(i in Range(99))
{
/* stuff goes here */
}
Note that the range given is half-open (C++ iterator `[begin,end)` style).
Both the beginning and end of the range must be compile-time constant expressions that Slang knows how to constant-fold.
The implementation will basically generate code for `/* stuff goes here */` N times, once for each value in the half-open range.
Each time, the variable `i` will be replaced with a different compile-time-constant expression.
While I was working on a test case for this, I also found that our build of glslang had an issue with resource limits, so I fixed that.
Clients will need to build a new glslang to use the fix.
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Falcor shadow fixes
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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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This is a straightforward mapping given the infrastructure already in place.
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