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* Adding support for global uniform shader parameters
This change adds support for Slang programmers to declare shader parameters of "ordinary" types at global scope:
```hlsl
uniform float gScaleFactor;
void main() { ... *= gScaleFactor; ... }
```
The generated HLSL/GLSL/DXIL/SPIR-V output will be something along the lines of:
```hlsl
struct GlobalParams
{
float gScaleFactor;
}
cbuffer globalParams
{
GlobalParams globalParams;
}
void main() { ... *= globalParams.gScaleFactor; ... }
```
The binding information used for the implicit `globalParams` constant buffer will be determined by the existing implicit parameter binding logic (which already had support for this kind of transformation).
The reason this change is being pursued right now is because it is one step toward removing the implicit `KernelContext` type that is used to wrap the generated code for our CPU and CUDA C++ targets. Handling global-scope parameters of ordinary type requires an IR pass that synthesizes the `GlobalParams` structure type above, and that step ends up removing the need for the similar `UniformState` structure that was being used in the CPU/CUDA emit logic.
A more detailed guide to the changes included follows:
* The diagnostic for a global-scope variable that is implicitly a shader parameter was kept, but changed to a warning. Users can opt out of the warning by decorating their parameter as a `uniform` (since that keyword is already being used to mark entry-point parameters that should be treated as uniform shader parameters).
* To simplify the task of finding the global shader parameters, the `CLikeSourceEmitter` type has been given an `m_irModule` member. The previous emit logic for `UniformState` was having to do a roundabout solution involving the `EmitAction`s to deal with not having direct access to the module.
* Removed a few dead declarations in the emit logic (related to a much earlier point where emit was based on the AST instead of the IR).
* Made the computation of type names in C++ emit take into account `ConstantBuffer<T>` and `ParameterBlock<T>`. As far as I can tell, these were being handled with some special-case hacks in the emit logic instead of being supported more fundamentally. It might actually be good to pass these through as `ConstantBuffer<T>` and `ParameterBlock<T>` in the C++ output, and allow the prelude to customize their translation (defaulting to defining them as `T*`).
* Removed the special-case C++ emit logic for references to global shader parameters. There are now at most two global shader parameters to deal with, and the default emit logic (referring to them by name) does the Right Thing.
* Changed the handling of entry points for C++ (both CPU and CUDA) so that it handles the bundled-up shader paameters for the global and entry-point scopes the same way. The main complication here is OptiX, where parameter data is passed very differently than it is for CUDA compute kernels.
* Reverted changes to `ir-entry-point-uniforms` that had made its logic depend on the compilation target. The parameter binding logic was already responsible for deciding if a given target needed to wrap up its entry-point parameters in a constant buffer, and the IR pass was respecting that layout information. The current workaround had been removing the `ConstantBuffer<T>` indirection from this IR pass for CPU/CUDA, but then reintroducing the same indirection later on in the emit step.
* Added an explicit IR pass with the task of collecting global-scope parameters of uniform/ordinary type and packaging them up into a `struct`, and then optionally packaging that `struct` up in a constant buffer. This pass bases its decisions on the IR layout information that was already computed, so it should match whatever policy choices were made at the layout level.
* Changed the "key" operand on IR `struct` layout information to not assume an `IRStructKey`. The problem here is that the global scope gets a `StructTypeLayout` to represent its members, and this is convenient (rather than having to always special-case logic that handles the global scope), but the "fields" of that struct are global variables which do not have `IRStructKey`s associated with them. The simplest solution is to use the variables themselves as the keys, which required removing the assumption in the IR encoding.
* Updated the IR layout process to compute a layout for the global scope of an entire program, and to attach that to the `IRModule` via a decoration. Updated the IR linking process to carry through that decoration to the linked output. This is necessary so that the IR pass that transforms global parameters can access the global-scope layout information.
An important concern with this approach is that the contents and layout of the monolithic `GlobalParams` structure depends on the exact set of modules that were linked (and the order in which they were specified, in some cases). This isn't really a new thing with this change, but it becomes more important as we start to think of how to generalize things to better support separate compilation and linking.
There are changes that can (and should) be made to the way that IR layouts are computed for programs (e.g., so that we compute layout per-module and then combine them rather than as a whole-program step). In this case, the problem of forming the combined/linked global layout can be moved down the IR level and not be reliant on AST-level information.
Just changing the way layout and linking interact would not change the fundamental problem that global shader parameters as they currently exist in Slang/HLSL/GLSL are not readily compatible with true separate compilation. We either need to find a solution strategy that we can apply to allow existing shaders to work with separate compilation *or* we need to incrementally work toward removing support for global-scope shader parameters in favor of explicit entry-point parameters in all cases.
* fixup: missing files
* fixup: comment the new code
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This PR introduces support for the public modifier for functions. This
keyword allows labelled functions to be written to the compiled without
having a link to an entry point. The goal of this change is to help
support heterogeneous design of Slang by permitting C++ code to interact
with CPU slang functions.
Internally, this PR adds the public decoration to the IR and defines a
lowering from the public modifier in the AST to this decoration.
Additionally, the Keep Alive decoration is added to any public modifier
being lowered, which prevents DCE from eliminating functions labelled
with the public keyword.
Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>
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* Add a test case for dynamic dispatch with `This` type in interface decl.
* Update comments
* fix typo in comments
Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>
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* Multiple Entry Point Cleanup
This commit provides some in-code cleanup of the previous multiple entry point PR (#1411). Specifically, this PR provides refactoring of multiple entry point functions into helper functions, the removal of the EntryPointAndIndex struct, and various stylistic improvements.
* Minor updates
Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>
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* ShortList<T> and core.natvis improvements.
* Fix gcc build.
* add `getBuffer()` accessor to `GetArrayViewResult`
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Co-authored-by: Yong He <yhe@nvidia.com>
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* Attempt to silence some warnings
This is an attempt to change code in `slang-ast-serialize.cpp` so that it doesn't trigger a warning(-as-error) in one of our build configurations.
The original code is fine in terms of expressing its intent, so the right answer might actually be to silence the warning.
* fixup: make sure to actually initialize
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(#1420)
* Fix handling of UniformState from #1396
* * Fix bug in slang-dxc-support where it didn't get the source path correctly
* Make entryPointIndices const List<Int>&
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There was a small but non-trivial amount of code across `IRModule`, the `ObjectScopeManager`, and `StringRepresentationCache` that had to do with managing the lifetimes of `RefObject`s that might be referenced by IR instructions (and thus need to be kept alive for the lifetime of the IR module).
We have long since migrated to a model where IR instruction do not include owned references to `RefObject`s, so these facilities weren't actually needed. This streamlines `IRModule`'s declaration, and trims code that we aren't actually using.
One note for the future is that the `StringRepresentationCache` no longer does what its name implies (it is not a cache of `StringRepresentation`s), so we should consider giving it a more narrowly scoped name. I didn't include that in this change because I wanted to keep the diffs narrow and easy to review.
A follow-on renaming change should be trivial if/when we can agree on what the type should be called at this point. Alternatively, we could simply bake the functionality of `StringRepresentationCache` into he IR deserialiation logic itself, since that is the only code using it.
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* Initial work on property declarations
Introduction
============
The main feature added here is support for `property` declarations, which provide a nicer experience for working with getter/setter pairs.
If existing code had something like this:
```hlsl
struct Sphere
{
float4 centerAndRadius; // xyz: center, w: radius
float3 getCenter() { return centerAndRadius.xyz; }
void setCenter(float3 newValue) { centerAndRadius.xyz = newValue; }
// similarly for radius...
}
void someFunc(in out Sphere s)
{
float3 c = s.getCenter();
s.setCenter(c + offset);
}
```
It can be expressed instead using a `property` declaration for `center`:
```hlsl
struct Sphere
{
float4 centerAndRadius; // xyz: center, w: radius
property center : float3
{
get { return centerAndRadius.xyz; }
set(newValue) { centerAndRadius.xyz = newValue; }
}
// similarly for radius...
}
void someFunc(in out Sphere s)
{
float3 c = s.center;
s.center = c + offset;
}
```
The benefits at the declaration site aren't that signficiant (e.g., in the example above we actually have slightly more lines of code), but the improvement in code clarity for users is significant.
Having `property` declarations should also make it easier to migrate from a simple field to a property with more complex logic without having to first abstract the use-site code using a getter and setter.
An important future benefit of `property` syntax will be if we allow `interface`s to include `property` requirements, and then also allow those requirements to be satisfied by ordinary fields in concrete types.
Subscripts
----------
The Slang compiler already has limited (stdlib-use-only) support for `__subscript` declarations, which are conceptually similar to `operator[]` from the C++ world, but are expressed in a way that is more in line with `subscript` declarations in Swift. A `SubscriptDecl` in the AST contains zero or more `AccessorDecl`s, which correspond to the `get` and `set` clauses inside the original declaration (there is also a case for a `__ref` accessor, to handle the case where access needs to return a single address/reference that can be atomically mutated).
A major goal of the implementation here is to re-use as much of the infrastructure as possible for `__subscript` declarations when implementing `property` declarations.
Nonmutating Setters
-------------------
One additional thing added in this change is the ability to mark a `set` accessor on either a subscript or a property as `[nonmutating]`, and indeed all of the existing `set` accessors declared in the stdlib have been marked this way.
The need for this modifier is a bit subtle. If we think about a typical subscript or property:
```hlsl
struct MyThing
{
int f;
property p : int
{
get { return f; }
set(newValue) { f = newValue; }
}
}
```
it is clear we want the `set` accessor to translate to output HLSL as something like:
```
void MyThing_p_set(inout MyThing this, int newValue)
{
this.f = newValue;
}
```
Note how the implicit `this` parameter is `inout` even though we didn't mark anything as `[mutating]`. This is the obvious thing a user would expect us to generate given a property declaration.
Now consider a case like the following:
```hlsl
struct MyThing
{
RWStructuredBuffer<int> storage;
property p : int
{
get { return storage[0]; }
set(newValue) { storage[0] = newValue; }
}
}
```
This new declaration doesn't require (or want) an `inout` `this` parameter at all:
```
void MyThing_p_set(MyThing this, int newValue)
{
this.storage[0] = newValue;
}
```
In fact, given the limitations in the current Slang compiler around functions that return resource types (or use them for `inout` parameters), we can only support a `set` operation like this if we can ensure that the `this` parameter is considered to be `in` instead of `inout`. This is exactly the behavior we allow users to opt into with a `[nonmutating] set` declaration.
All of the subscript operations in the stdlib today have `set` accessors that don't actually change the value of `this` that they act on (e.g., storing into a `RWStructuredBuffer` using its `operator[]` doesn't change the value of the `RWStructuredBuffer` variable -- just its contents).
We'd gotten away without this detail so far just because `set` accessors were only being declared in the stdlib and they were all implicitly `[nonmutating]` anyway, so it never surfaced as an issue that the code we generated assumed a setter wouldn't change `this`.
Implementation
==============
Parser and AST
--------------
Adding a new AST node for `PropertyDecl` and the relevant parsing logic was mostly straightforward. The biggest change was allowing a `set` declaration to introduce an explicit name for the parameter that represents the new value to be set.
This change also adds a `[nonmutating]` attribute as a dual to `[mutating]`, for reasons I will get to later.
Semantic Checking
-----------------
The `getTypeForDeclRef` logic was updated to allow references to `property` declarations.
Some of the semantic checking work for subscripts was pulled out into re-usable subroutines to allow it to be shared by `__subscript` and `property` declarations.
The checking of accessor declarations, which sets their result type based on the type of the outer `__subscript` was changed to also handle an outer `property`.
Some special-case logic was added for checking of `set` declarations to make sure that their parameter is given the expected type.
Some logic around deciding whether or not `this` is mutable had to be updated to correctly note that `this` should be mutable by default in a `set` accessor, with an explicit `[nonmutating]` modifier required to opt out of this default. (This is the inverse of how a typical method or `get` accessor works).
IR Lowering
-----------
The good news is that after IR lowering, access to properties turns into ordinary function calls (equivalent to what hand-written getters and setters would produce), so that subsequent compiler steps (including all the target-specific emit logic) doesn't have to care about the new feature.
The bad news is that adding `property` declarations has revealed a few holes in how IR lowering was handling `__subscript` declarations and their accessors, so that it didn't trivially work for the new case as-is.
The IR lowering pass already has the `LoweredValInfo` type that abstractly represents a value that resulted from lowering some AST code to the IR. One of the cases of `LoweredValInfo` was `BoundSubscript` that represented an expression of the form `baseVal[someIndex]` where the AST-level expression referenced a `__subscript` declaration. The key feature of `BoundSubscript` is that it avoided deciding whether to invoke the getter, the setter, or both "too early" and instead tried to only invoke the expected/required operations on-demand.
This change generalizes `BoundSubscript` to handle `property` references as well, so it changes to `BoundStorage`. Making the type handle user-defined property declarations required fixing a bunch of issues:
* When building up argument lists in the IR, we need to know whether an argument corresponds to an `in` or an `out`/`inout` parameter, to decide whether to pass the value directly or a pointer to the value. Some of the logic in the lowering pass had been playing fast and loose with this, so this change tries to make sure that whenever we care computing a list of `IRInst*` that represent the arguments to a call we have the information about the corresponding parameter.
* Similarly, when emitting a call to an accessor in the IR, the information about the expected type of the callee was missing/unavailable, and the code was incorrectly building up the expected type of the callee based on the types of the arguments at the call site. The logic has been changed so that we can extract the expected signature of an accessor (how it will be translated to the IR) using the same logic that is used to produce the actual `IRFunc` for the accessor (so hopefully both will always agree).
* Dealing with `in` vs. `inout` differences around parameters means also dealing with the "fixup" code that is used to assign from the temporary used to pass an `inout` argument back into the actual l-value expression that was used. That logic has all been hoisted out of the expression visitor(s) and into the global scope.
Future Work
===========
The entire approach to handling l-values in the IR lowering pass is broken, and it is in need a of a complete rewrite based on new first-principles design goals. While something like `LoweredValInfo` is decent for abstracting over the easy cases of r-values, addresses, and a few complicated l-value cases like swizzling, it just doesn't scale to highly abstract l-values like we get from `__subcript` and `property` declarations, nor other corner cases of l-values that we need to handle (e.g., passing an `int` to an `inout float` parameter is allowed in HLSL, and performs conversions in both directions!).
It Should be Easy (TM) to extend the logic that tries to synthesize an interface conformance witness method when there isn't an exact match to also support synthesizing a property declaration (plus its accessors) to witness a required property when the type has a field of the same name/type.
* fixup: pedantic template parsing error (thanks, clang!)
* fixup: cleanups and review feedback
* Removed some `#ifdef`'d out code from merge change
* Added proper diagnostics for accessor parameter constraints, which led to some fixes/refactorings
* Added a test case for the accessor-related diagnostics
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* Backend for Multiple Entry Points
Introduces the basic backend on the compiler for zero or more entry
points. Entry points have been extended to lists for several functions,
with loopFunctions have been extended to take in entry points and
indices as appropriate, to allow for multiple entry points once the
frontend is expanded. Several functions are currently being assumed to
have a single entry point for simplicity and provide a work in progress
commit.
* Progress on debugging fixes
* Tests passing
* Refactored emitEntryPoints
* Updated lists to be by constant reference
* Fixes to formatting
* Refactoring updates for the compiler
* Fix for compilation errors
* Reformatting
* More reformatting
* Moved struct around to help with compilation
Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>
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* Try to fix problem with C++ extractor concating tokens producing an erroneous result.
* Improve naming/comments around C++ extractor fix.
* Another small improvement around space concating when outputing token list.
* Handle some more special cases for consecutive tokens for C++ extractor concat of tokens.
* WIP AST serialization.
* Comment out so compile works.
* More work on AST serialization.
* WIP AST serialize.
* WIP AST Serialization - handling more types.
* WIP: Compiles but not all types are converted, as not all List element types are handled.
* Compiles with array types.
* Finish off AST serialization of remaining types.
* Remove ComputedLayoutModifier and TupleVarModifier.
* Add fields to ASTSerialClass type.
* Construct AST type layout.
* AST Serialization working for writing to ASTSerialWriter.
* Removed call to ASTSerialization::selfTest in session creation.
* Fixes for gcc.
* Diagnostics handling - better handling of dashify.
* Improve comment around DiagnosticLookup.
* Updated VS project.
* Write out as a Stream, taking into account alignment.
* First pass at serializing in AST.
* Added support for deserializing arrays.
* Small bug fixes.
* Fix problem calculating layout.
Split out loading on entries.
* Fix typo in AST conversion.
* Add some flags to control AST dumping.
* Fix bug from a typo.
* Special case handling of Name* in AST serialization.
* Special case handling of Token lexemes, make Names on read.
* Documentation on AST serialization.
* ASTSerialTestUtil - put AST testing functions.
Fix typo that broke compilation.
* Fix typo.
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* Try to fix problem with C++ extractor concating tokens producing an erroneous result.
* Improve naming/comments around C++ extractor fix.
* Another small improvement around space concating when outputing token list.
* Handle some more special cases for consecutive tokens for C++ extractor concat of tokens.
* WIP AST serialization.
* Comment out so compile works.
* More work on AST serialization.
* WIP AST serialize.
* WIP AST Serialization - handling more types.
* WIP: Compiles but not all types are converted, as not all List element types are handled.
* Compiles with array types.
* Finish off AST serialization of remaining types.
* Remove ComputedLayoutModifier and TupleVarModifier.
* Add fields to ASTSerialClass type.
* Construct AST type layout.
* AST Serialization working for writing to ASTSerialWriter.
* Removed call to ASTSerialization::selfTest in session creation.
* Fixes for gcc.
* Diagnostics handling - better handling of dashify.
* Improve comment around DiagnosticLookup.
* Updated VS project.
* Write out as a Stream, taking into account alignment.
* First pass at serializing in AST.
* Added support for deserializing arrays.
* Small bug fixes.
* Fix problem calculating layout.
Split out loading on entries.
* Fix typo in AST conversion.
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-Lower interfaces into actual `IRInterfaceType` insts.
-Lower `DeclRef<AssocTypeDecl>` into `IRAssociatedType`
-Generate proper IRType for generic functions.
-Add a test case exercising dynamic dispatching a generic static function through an associated type.
-Bug fixes for the test case.
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* Try to fix problem with C++ extractor concating tokens producing an erroneous result.
* Improve naming/comments around C++ extractor fix.
* Another small improvement around space concating when outputing token list.
* Handle some more special cases for consecutive tokens for C++ extractor concat of tokens.
* WIP AST serialization.
* Comment out so compile works.
* More work on AST serialization.
* WIP AST serialize.
* WIP AST Serialization - handling more types.
* WIP: Compiles but not all types are converted, as not all List element types are handled.
* Compiles with array types.
* Finish off AST serialization of remaining types.
* Remove ComputedLayoutModifier and TupleVarModifier.
* Add fields to ASTSerialClass type.
* Construct AST type layout.
* AST Serialization working for writing to ASTSerialWriter.
* Removed call to ASTSerialization::selfTest in session creation.
* Fixes for gcc.
* Diagnostics handling - better handling of dashify.
* Improve comment around DiagnosticLookup.
* Updated VS project.
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struct-inheritance-and-interfaces
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The main new feature that works here is that a derived `struct` type can satisfy one or more interface requirements using methods it inherited from a base `struct` type:
```hlsl
interface ICounter { [mutating] void increment(); }
struct CounterBase { int val; [mutating] void increment() { val++; } }
struct ResetableCounter : CounterBase, ICounter
{
[mutating] void reset() { val = 0; }
}
```
Here the derived `ResetableCounter` type is satisfying the `increment()` requirement from `ICounter` using the inherited `CounterBase` method instead of one defined on `ResetableCounter`.
The crux of the problem here was that after lowering to HLSL/GLSL, the above code looks something like:
```hlsl
struct CounterBase { int val; };
void CounterBase_increment(in out CounterBase this) { this.val++; }
struct ResetableCounter { CounterBase base; }
void ResetableCounter_reset(in out ResetableCounter this) { this.base.val = 0; }
```
The central problem is that `CounterBase_increment` here is not type-compatible what we expect to find in the witness table for `ResetableCounter : ICounter`: the `this` parameter has the wrong type!
The basic solution strategy here is to intercept the search for a witness to sastify an interface requirement in `findWitnessForInterfaceRequirement` (those witnesses get collected into a witness table). The revised logic first looks for an exact match, which will only consider members introduced for the type itself, and not those introduced by base types.
If an exact match for a method requirement is not found, the semantic checker then tries to *synthesize* a witness for the requirement, which more or less amounts to generating a function like:
```hlsl
[mutating] void ResetableCounter::synthesized_increment()
{
this.increment();
}
```
The body of that synthesized method will type-check just fine in this case (because it desugars into `this.base.increment()`, more or less), and thus the synthesized method declaration can be used as the actual witness that drives downstream code generation.
Details:
* I added some options to lookup to allow us to explicitly skip member lookup through base interfaces; this should make sure that we don't accidentally satisfy an interface requirement using a member of the same or another interface (since such members are conceptually `abstract`).
* As it originally stood, the semantic checker was allowing `CounterBase.increment()` to satisfy the `increment()` requirement of `ResetableCounter` directly, with the result that we got invalid HLSL/GLSL code as output. In order to avoid this and other bad cases, I made sure that the "exact match" case of requirement satisfaction ignores members that included any "breadcrumbs" in the lookup result item (since the breadcrumbs would all indicate transformations that needed to be applied to `this` to find the right member).
* If we eventually have targets where `this` is passed by pointer/reference in all cases, then all of this work is not needed for the common case of single inheritance, and the base-type method should be usable as a witness directly. I don't see any easy way to handle that special case without producing target-dependent code in the front-end. It might be that we need an IR pass that can detect functions that are trivial "forwarding" functions and replace them with the function they forward to.
* This change includes a test case that should have come along with the original PR that started adding struct inheritance
Caveats:
* The comments in this change talk about things like allowing a method with a default parameter to satisfy a requirement without that parameter. That scenario won't actually work at present because we still have an enormous hack in our logic for checking methods against requirements: we don't actually consider their signatures! I couldn't fold a fix for that issue into this change because there are subtle corner cases around associated types that we need to handle correctly (which were part of the reason why the checking is as hacked as it is)
* This change does *not* try to test or address the case where we want to have a `Derived` type conform to `ISomething` because it inherits from `Base` and `Base : ISomething`. That case has its own details that need to be worked out, but ideally can follow a similar implementation strategy when it comes to re-using methods from `Base` to satisfy requirement on `Derived`.
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* Associate a downstream compiler for prelude lookup even if output is source.
* Remove LanguageStyle and just use SourceLanguage instread.
* Added set/getPrelude.
Made prelude work on source language.
* Fix typo in method name replacement.
get/SetPrelude get/setLanguagePrelude
* Fix issue because of method name change.
* Remove getPreludeDownstreamCompilerForTarget
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* * Fix output in slang repro command line
* Profile uses lowerCamel method names (had mix of upper and lower)
* Rename slang-serialize-state/SerializeStateUtil to slang-repro and ReproUtil.
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* * Remove UniformState and UniformEntryPointParams types
* Put all output C++ source in an anonymous namespace
* If SLANG_PRELUDE_NAMESPACE is set, make what it defines available in generated file.
* Fix signature issue in performance-profile.slang
* Context -> KernelContext to avoid ambiguity.
* Fix issues around dynamic dispatch and anonymous namespace.
* Fix typo.
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(#1395)
Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>
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This was an oversight in the stdlib, and the `!=` definition follows the `==` in a straightforward fashion.
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* Add IR pass to lower generics into ordinary functions.
* Fix project files
* Emit dynamic C++ code for simple generics and witness tables.
Fixes #1386.
* Remove -dump-ir flag.
* Fixups.
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* Releases compile request if there is an error.
* Arrange so that caller can clean up CompileRequest so don't have to capture all paths.
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Fixes #890.
Co-authored-by: Tim Foley <tfoleyNV@users.noreply.github.com>
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* Remove implicit conversions to `void`
Fixes #1372
The standard library code had accidentally introduced implicit-conversion `__init` operations on the `void` type that accepted each of the other basic types, so that a function written like:
```hlsl
void bad() { return 1; }
```
would translate to:
```hlsl
void bad() { return (void)1; }
```
The dual problesm are that the input code should have produced a diagnostic of some kind, and the output code doesn't appear to compile correctly through fxc.
This change introduces several fixes aimed at this issue:
* First, the problem in the stdlib code is plugged: we don't introduce implicit conversion operations *to* or *from* `void` (we'd only been banning it in one direction before)
* Next, an explicit `__init` was added to `void` that accepts *any* type so that existing HLSL code that might do `(void) someExpression` to ignore a result will continue to work. This is a compatibility feature, and it might be argued that we should at least warn when it is used. Note that this function is expected to never appear in output HLSL/GLSL because its result will never be used, and it is marked `[__readNone]` allowing calls to it to be eliminated as dead code.
* During IR lowering, we now take care to only emit the `IRReturnVal` instruction type if there is a non-`void` value being returned, and use `IRReturnVoid` for both the case where no expression was used in the `return` statement *and* the case where an expression of type `void` is returned.
* A test case was added to confirm that returning `1` from a `void` function isn't allowed, while returning `(void) 1` *is*.
The net result of these changes is that we now produce an error for the bad input code, we allow explicit casts to `void` as a compatibility feature, and we are more robust about treating `void` as if it is an ordinary type in the front-end.
* fixup: missing file
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IRWitnessTable values (#1387)
* Generate IRType for interfaces, and use them as the type of IRWitnessTable values.
This results the following IR for the included test case:
```
[export("_S3tu010IInterface7Computep1pii")]
let %1 : _ = key
[export("_ST3tu010IInterface")]
[nameHint("IInterface")]
interface %IInterface : _(%1);
[export("_S3tu04Impl7Computep1pii")]
[nameHint("Impl.Compute")]
func %Implx5FCompute : Func(Int, Int)
{
block %2(
[nameHint("inVal")]
param %inVal : Int):
let %3 : Int = mul(%inVal, %inVal)
return_val(%3)
}
[export("_SW3tu04Impl3tu010IInterface")]
witness_table %4 : %IInterface
{
witness_table_entry(%1,%Implx5FCompute)
}
```
* Fixes per code review comments.
Moved interface type reference in IRWitnessTable from their type to operand[0].
* Fix typo in comment.
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* Diagnose circularly-defined constants
Work on #1374
This change diagnoses cases like the following:
```hlsl
static const int kCircular = kCircular;
static const int kInfinite = kInfinite + 1;
static const int kHere = kThere;
static const int kThere = kHere;
```
By diagnosing these as errors in the front-end we protect against infinite recursion leading to stack overflow crashes.
The basic approach is to have front-end constant folding track variables that are in use when folding a sub-expression, and then diagnosing an error if the same variable is encountered again while it is in use. In order to make sure the error occurs whether or not the constant is referenced, we invoke constant folding on all `static const` integer variables.
Limitations:
* This only works for integers, since that is all front-end constant folding applies to. A future change can/should catch circularity in constants at the IR level (and handle more types).
* This only works for constants. Circular references in the definition of a global variable are harder to diagnose, but at least shouldn't result in compiler crashes.
* This doesn't work across modules, or through generic specialization: anything that requires global knowledge won't be checked
* fixup: missing files
* fixup: review feedback
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Fixes #1377
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