| Commit message (Collapse) | Author | Age |
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* Prefixing source files in source/slang with slang-
* Prefix source in source/slang with slang- prefix.
* Rename core source files with slang- prefix.
* Update project files.
* Fix problems from automatic merge.
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* List made members m_
Tweaked types to closer match conventions.
* Use asserts for checking conditions on List.
Other small improvements.
* List<T>.Count() -> getSize()
* List<T>
Add -> add
First -> getFirst
Last -> getLast
RemoveLast -> removeLast
ReleaseBuffer -> detachBuffer
GetArrayView -> getArrayView
* List<T>::
AddRange -> addRange
Capacity -> getCapacity
Insert -> insert
InsertRange -> insertRange
AddRange -> addRange
RemoveRange -> removeRange
RemoveAt -> removeAt
Remove -> remove
Reverse -> reverse
FastRemove -> fastRemove
FastRemoveAt -> fastRemoveAt
Clear -> clear
* List<T>
FreeBuffer -> _deallocateBuffer
Free -> clearAndDeallocate
SwapWith -> swapWith
* List<T>
SetSize -> setSize
Reserve -> reserve
GrowToSize growToSize
* UnsafeShrinkToSize -> unsafeShrinkToSize
Compress -> compress
FindLast -> findLastIndex
FindLast -> findLastIndex
Simplify Contains
* List<T>
Removed m_allocator (wasn't used)
Swap -> swapElements
Sort -> sort
Contains -> contains
ForEach -> forEach
QuickSort -> quickSort
InsertionSort -> insertionSort
BinarySearch -> binarySearch
Max -> calcMax
Min -> calcMin
* Initializer::Initialize -> initialize
List<T>::
Allocate -> _allocate
Init -> _init
IndexOf -> indexOf
* * Put #include <assert.h> in common.h, and remove unneeded inclusions
* Small refactor of ArrayView - remove stride as not used
* getSize -> getCount
setSize -> setCount
unsafeShrinkToSize->unsafeShrinkToCount
growToSize -> growToCount
m_size -> m_count
* Some tidy up around Allocator.
* Use Index type on List.
* Refactor of IntSet.
First tentative look at using Index.
* Made Index an Int
Did preliminary fixes.
Made String use Index.
* Partial refactor of String.
* String::Buffer -> getBuffer
ToWString -> toWString
* Small improvements to String.
String::
Buffer() -> getBuffer()
Equals() -> equals
* Try to use Index where appropriate.
* Fix warnings on windows x86 builds.
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Fixes #858
The `precise` keyword exists in both HLSL and GLSL and when applied to a variable declaration is supposed to indicate that all computations that contribute to the value of that variable should not be altered based on "fast-math" optimizations. The main examples are that separate multiply and add operations should not be turned into fused multiply-add (fma) operations, and that operations cannot ignore the possibility of infinity or not-a-number values (e.g., by assuming that `x * 0.0f` is always `0.0f`).
(Aside: it is possible that my understanding of what the semantics of `precise` are in HLSL and GLSL is imperfect so that either the GLSL variant isn't sufficient to provide the semantics of the HLSL keyword, or that the definition of "all computations that contribute" to a value isn't actually correct. We may need to revise this implementation based on subsequent learnings.)
The basic idea here is to turn the AST `precise` keyword into a `[precise]` decoration in the IR and then emit that as a `precise` keyword again in the output.
The main catch is that whereas most of our existing IR decorations apply to things like global shader parameters or `struct` members that usually stick around for the duration of compilation, `[precise]` will get slapped on local variables that will often get optimized away by our SSA pass. There are two ways a variable can get eliminated/replaced during the SSA pass:
1. A use of the variable can be replaced with an ordinary instruction that computes its value.
2. A use of the variable can be replaced with a reference to a "phi node" that will take on the appropriate value based on control flow.
These two cases already had logic to copy a "name hint" decoration from the variable over to an instruction that will replace it, and I simply extended them to also propagate over a `[precise]` decoration.
The test case added with this change intentionally constructs a case where `[precise]` needs to be propagated over to an SSA "phi node" in order to generate correct output code.
The other gotcha is that we can emit variable declarations in various places in `emit.cpp`, and all of these needed to handle `[precise]`. Not only do we have actually local variables (`IRVar`), but we also have SSA phi nodes (`IRParam`), and then there are cases where an intermediate computation (an ordinary instruction) should be `[precise]` and thus we need to emit it as a temporary (not folding it into its use sites) and make sure that the temporary itself gets the `precise` keyword.
I have manually confirmed that in the output SPIR-V, this change results in the `NoContraction` SPIR-V decoration being added to the relevant operations, and the output DXBC contains a multiply and an add in place of a multiply-add. The output DXIL does not show any obvious changes due to `precise`, although the exact order and operands of the math instructions emitted does differ when `precise` is added/removed. In all cases the output is equivalent to hand-written HLSL/GLSL with a `precise`-qualified local variable.
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* Initial support for dynamic dispatch using "tagged union" types
Suppose a user declares some generic shader code, like the following:
```hlsl
interface IFrobnicator { ... }
type_param T : IFrobincator;
ParameterBlock<T : IFrobnicator> gFrobnicator;
...
gFrobincator.frobnicate(value);
```
and then they have some concrete implementations of the required interface:
```hlsl
struct A : IFrobnicator { ... }
struct B : IFrobnicator { ... }
```
The current Slang compiler allows them to generate distinct compiled kernels for the case of `T=A` and the case of `T=B`. This means that the decision of which implementation to use must be made at or before the time when a shader gets bound in the application.
This change adds a new ability where the Slang compiler can generate code to handle the case where `T` might be *either* `A` or `B`, and which case it is will be determined dynamically at runtime. This means a single compiled kernel can handle both cases, and the decision about which code path to run can be made any time before the shader executes.
This new option is supported by defining a *tagged union* type. Via the API, the user specifies that `T` should be specialized to `__TaggedUnion(A,B)` (the double underscore indicates that this is an experimental and unsupported feature at present). We refer to the types `A` and `B` here as the "case" types of the tagged union. Conceptually, the compiler synthesizes a type something like:
```hlsl
struct TU { union { A a; B b; } payload; uint tag; }
```
The user can then allocate a constant buffer to hold their tagged union type, and when they pick a concrete type to use (say `B`), they fill in the first `sizeof(B)` bytes of their buffer with data describing a `B` instance, and then set the `tag` field to the appopriate 0-based index of the case type they chose (in this case the `B` case gets the tag value `1`).
Actually implementing tagged unions takes a few main steps:
* Type parsing was extended to special-case `__TaggedUnion` as a contextual keyword. This is really only intended to be used when parsing types from the API or command-line, and Bad Things are likely to happen if a user ever puts it directly in their code. Eventually construction of tagged unions should be an API feature and not part of the language syntax.
* Semantic checking was extended to recognize that a tagged union like `__TaggedUnion(A,B)` shoud support an interface like `IFrobnicator` whenever all of the case types suport it, as long as the interface is "safe" for use with tagged unions (which means it doesn't use a few of the advancd langauge features like associated types).
* The IR was extended with instructions to represent tagged union types and to extract their tag and the payload for the different cases as needed.
* IR generation was extended to synthesize implementations of interface methods for any interface that a tagged union needs to support. Right now the implementation is simplistic and only handles simple method requirements, which it does by emitting a `switch` instruction to pick between the different cases.
* A new IR pass was introduced to "desugar" any tagged union types used in the code. The downstream HLSL and GLSL compilers don't support `union`s, so we have to instead emit a tagged union as a "bag of bits" and implement loading the data for particular cases from it manually.
* Final code emit mostly Just Works after the above steps, but we had to introduce an explicit IR instruction for bit-casting to handle the output of the desugaring pass.
There are a bunch of gaps and caveats in this implementation, but that seems reasonable for something that is an experimental feature. The various `TODO` comments and assertion failures in unimplemented cases are intended, so that this work can be checked in even if it isn't feature-complete.
* fixup: missing files
* fixup: typos
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* Make a test case use IR serialization
* Make all IR instructions usable as parents
This makes it so that every `IRInst` has the list of children that used to be on `IRParentInst` and eliminates `IRParentInst`.
Most places in the code were only checking against `IRParentInst` so that they could know whether there were child instructions to iterate over.
This change bloats the size of every instruction by two pointers, but we hope to be able to eliminate that overhead with a better encoding later.
* Change IR decorations to be instructions.
The main change here is that `IRDecoration` now inherits from `IRInst`, and `IRInst` now has a single linked list that holds both decorations *and* children.
At each point where code used to loop over `getChildren()` on an `IRInst`, I checked whether it made sense to leave the operation as processing just the children, or if it should process both decorations and children.
The thorniest bit was making sure the logic for inserting an instruction into a parent is correct. For the most part, once IR code is built all insertions are explicitly before/after another instruction, so the ordering can't get messed up. The sticking point is any code that does an explicit `insertAtStart` or `insertAtEnd`, but I surveyed those to make sure they are correct in context, and I also made all insertions bottleneck through one routine that does a better job of asserting the preconditions than what was there before. We may still want a "smart" insertion function at some point so that if somebody does `someDecoration->insertAtEnd(someInst)` the decoration intelligently goes to the end of the decoration list, and not the entire decorations-and-children list.
All of the existing decoration types were refactored to provide accessors for their operands, rather than directly exposing fields. In most cases the operands are required to be `IRConstant` nodes of fixed types. Not all of these types need to be kept around in the new approach, but they were left in so that as much existing code as possible can be kept working.
The `IRBuilder` was extended with factory functions to make the various decoration types and attach them.
All the fields in concrete decorations that were using `StringRepresentation` or `Name` pointers are now using IR-level string operands which provide their value as an `UnownedStringSlice`, so logic that was working with those decoration values needed to be updated here and there. I also needed to add the logic to clone string-literal values to the IR cloning pass, since they are now being used in almost every piece of code.
A new type of constant IR instruction for literal pointers was added, to handle the cases where an IR decoration needs an operand that is a raw AST-level pointer. These are even being serialized, although we obviously should not rely on them to round-trip through serialization in the future. Ideally, a follow-on change should add a cleanup pass where we remove any decorations from a module that shouldn't be allowed in the serialized code.
The biggest overall cleanup is in the serialization logic, where a lot of code just disappears because it can process the raw "decorations and children" list as the logical children of an IR instruction. The only special cases left are literals (which seem like they will always need special-casing) and global values (because they have a mangled name, which we plan to move into a decoration).
One other example of a simplification made possible by this change: the `IRNotePatchConstantFunc` instruction was implemented as an instruction only because it couldn't be encoded as a decoration at the time (it needed to have an operand that referenced an IR function).
The IR dumping logic was also updated (which meant a change to the `ir/string-literal` test) to try to make it print out all decorations a bit more systematically now that they are encoded like other instructions. The formatting isn't quite perfect, but it is good enough to be able to read what is going on.
I didn't include updates to the validation logic to ensure that decorations are being added in ways that follow the invariants, but that would be a nice thing to add next.
* fixup: 64-bit issues
* fixup: forward declaration issues
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Fixes #723
This fixes a case where the SSA construction pass wasn't dealing with the possibility of a phi node that it had provisionally introduced being replaced later. The result was invalid IR (caught with `-validate-ir`) that referenced an instruction nowhere in the IR module (because it was dropped).
The fix centralizes the code for dealing with phi nodes that have been replaced, so that the two different paths where variables get "read" during SSA construction can both use the same logic.
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* Cleanups around behavior when the compiler fails
* Add another case where we try to `noteInternalErrorLoc()` if an exception in thrown. This one is the in the logic for emitting an IR instruciton. This could be improved by adding another layer at the function level (as a catch-all for instructions with no location), but something is better than nothing.
* Change a bunch of `assert()`s over to `SLANG_ASSERT()`s, so that we can theoretically take more control over them (e.g., make release builds with asserts enabled)
* Some other small cleanups around the assertions we perform.
In the survey I made, I didn't really see many obvious "smoking gun" cases where we could produce a significantly better error message for some of the unimplemented/unexpected paths, other than to actually implement the missing functionality.
* fixup
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This code is currently not used by anything, but I wanted to check in a first pass at an implementation of dominator tree construction so that we don't have to keep avoiding implementing algorithms that rely on having dominator information available.
The algorithm used to construct the dominator tree is taken from "A Simple, Fast Dominance Algorithm" by Keith D. Cooper, Timothy J. Harvey, and Ken Kennedy.
This is not the "best" algorithm in terms of asymptotic performance, but it is among the simplest algorithms for computing a dominator tree that still outperforms naive iterative set-based methods.
The actual data structure and API for the dominator tree has a bit of "cleverness" in it to try to make the common queries reasonably fast (e.g., you can check whether A dominates B in constant time).
My hope is that even if we implement a more advanced algorithm for constructing the dominator tree, we can retain compatibility with passes that might make use of this API.
Because no code is currently using this logic, I have done only minimal testing by stepping through this code and validating the results on paper for some very small CFGs.
More serious testing/debugging may need to wait until we have an optimization pass that needs the dominator tree we compute here.
One open question I have is how best to introduce traditional unit testing into Slang, since this is an example of code that would benefit greatly from being unit tested.
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The basic idea here is that when lowering to the IR, the front-end will attach a "name hint" to the IR instruction(s) that represent a given declaration, and then the passes that work on the IR will try to preserve and propagate those names, and then finally the emit logic will use them in place of mangled or unique names when available.
This change does *not* try to deal with the issues that arise when we try to use those variable names in the output without any modification (e.g., handling cases where they might clash with keywords or builtins in the target language). Instead, it tries to establish baseline behavior for propagating through names, so that a later change can concentrate on the issue of using those names exactly when it is legal to do so.
In order to avoid issues around the name "hints" causing problems we take two main steps:
1. We "scrub" each name to reduce it down to the allowed set of identifier characters in C-like languages, and then ensure that it doesn't do things that would be illegal in some downstream languages (e.g., consecutive underscores are not allowed in GLSL) or could clash with Slang's mangled names. This process isn't guaranteed to give distinct results for distinct inputs (it isn't a mangling scheme, after all).
2. We generate a unique ID for each occurence of a given name and always use that as a suffix. This means that even if a name happens to overlap with a keyword (if you somehow have a variable named `do`), we will still add a suffix that makes it not a problem (we'd output `do_0` which is fine).
The logic for generating these names is mostly straightforward. For simple variables, we use their given name directly, while for other declarations we try to form a name that includes their parent declaration (e.g. `SomeType.someMethod`).
Various IR passes need to propagate or preserve this information. The most interesting is type legalization, when we take a variable with an aggregate type and split some of the fields out into their own variables. In that case we generate "dotted" names like `someVar.someTexture` and rely on the emit logic to turn that into `someVar_someTexture`.
During SSA generation, if we are promoting a variable to SSA temporaries, we will try to propagate the name of the variable over to the temporaries (unless they already have a name from some other place). The same applies to block parameters ("phi nodes").
Many of the test changes need their expected output to be updated for this change. Luckily in most cases the output has gotten easier to understand.
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* Improve SSA promotion for arrays and structs
Fixes #518
The existing SSA pass would only handle `load(v)` and `store(v,...)`
where `v` is the variable instruction, and would bail out if `v` was
used as an operand in any other fashion.
The new pass adds support for `load(ac)` where `ac` is an "access chain"
with a gramar like:
ac :: v
| getElementPtr(ac, ...)
| getFieldAddress(ac, ...)
What this means in practical terms is that we can promote a local
variable of array or structure type to an SSA temporary even if there
are loads of individual elements/fields, as along as any *assignment* to
the variable assigns the whole thing.
I've added a test case to confirm that this change fixes passing of
arrays as function parameters for Vulkan.
* Fixup: disable test on Vulkan because render-test isn't ready
This is a fix for Vulkan, but I don't think our testing setup is ready
for it.
* Fixup: error in unreachable return case, caught by clang
* Fixups based on testing
These are fixes found when testing the original changes against the user code that originated the bug report.
* `emit.cpp`: Make sure to handle array-of-texture types when deciding whether to declare a temporary as a local variable in GLSL output
* `ir-legalize-types.cpp`: Make a not of a source of validation failures that we need to clean up sooner or later (just not in scope for this bug fix change).
* `ir-ssa.cpp`:
* When checking if something is an access chain with a promotable var at the end, make sure the recursive case recurses into the "access chain" logic instead of the leaf case
* Add some assertions to guard the assumption that any access chain we apply has been scheduled for removal
* Correctly emit an element *extract* instead of getting an element *address* when promoting an element access into an array being promoted
* Eliminate a wrapper routine that was setting up an `IRBuilder` and use the one from the block being processed in the SSA pass (since it was set up for stuff just like this)
* `ir-validate.cpp`
* Add a hack to avoid validation failures when running IR validation on the stdlib code. This case triggers for an initializer (`__init`) declaration inside an interface, since the logical "return type" is the interface type itself, which has no representation at the IR level and thus yields a null result type in a `FuncType` instruction.
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* Introduce an IR-level type system
Up to this point, the Slang IR has used the front-end type system to represent types in the IR.
As a result (but ultimately more importantly) the IR representation of generics and specialization has used AST-level concepts embedded in the IR.
For example, to express the specialization of `vector<T,N>` to a concrete type `float` for `T`, we needed an IR operation that could represent the specialization, with operands that somehow represented the type argument `float`.
The whole thing was very complicated.
The big idea of this change is to introduce a new representation in which types in the IR are just ordinary instructions, so that using them as operands makes sense. The hierarchy of IR types closely mirrors the AST-side hierarchy for now, and that will probably be something we should maintain going forward.
In order to make these changes work, though, I also had to do major overhauls of things like the way substitutions are performed, how we check interface conformances, the way lookup through interface types is done, etc. etc. This is a big change, and unfortunately any attempt to summarize it in the commit message wouldn't do it justice.
* Fix 64-bit build warning
* Fix up some clang warnings/errors
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The main practical change here is that things that used to be `IRValue`s, like literals, are now being expressed as instructions in the global scope.
In order to validate that things are actually being handled correctly, this change introduces an explicit "validation" pass that can be run on the IR to check for different invariants (although it doesn't check many of the important ones right now). I've left the validation pass turned off by default, but with a command-line flag to enable it. We may want to make it be on by default in debug builds, just to keep us honest. The main invariant for the moment is that when on IR instruction is used as an operand to another, it had better come from the same IR module.
Some of the existing passes were violating this rule, in particular when it came to cloning of witness tables related to global generic parameter substitution. Those features can in theory be handled better now by allowing `specialize` instructions at other scopes, but I didn't want to over-complicate this change, so I make just enough fixes to ensure that these steps always clone witness tables they get from the "symbols" on an IR specialization context. In order for this to work when recursively specializing, I had to ensure that the logic for generic specialization had a notion of a "parent" specialization context that it would fall back to to perform cloning when necessary.
This change keeps the logic that was caching and re-using the instructions for literal values within a module, but adds some logic that isn't really being tested right now for picking the right parent instruction to insert a constant instruction into. This logic doesn't trigger right now because all of the cases we are using it on have zero operands (and so they always get "hoisted" to the global scope), but eventually for things like types we want to be able to support instructions with operands (e.g., `vector<float, 4>`) and handle the case where some of those operands come from different scopes (e.g., when nested inside a generic).
The final change here is mostly cosmetic: the `IRBuilder` is now more abstract about where insertion occurs: it tracks a single `IRParentInst` to insert into, and then an optional `IRInst` to insert before. In the common case, that parent is an `IRBlock`, but it could conceivably also be the global scope, or a witness table, etc. Use sites where we used to change those fields directly now use distinct methods `setInsertInto(parent)` and `setInsertBefore(inst)` which capture the two cases we care about. Accessors are also defined to extract the current block (if the current parent is a block), and the current "function" (global value with code, if the current parent is a global value with code, or a block inside one).
With this work in place, it should be possible for a follow-on change to start putting `specialize` instructions at the global scope and thus clean up some of the on-the-fly specialization work. This work should also help with some of the requirements around a distinct IR-level type system and more explicit generics.
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* IR: "everything is an instruction"
This change tries to streamline the representation of the IR in the following ways:
* Every IR value is an instruction (there is no `IRValue` type any more)
* All IR values that can contain other values share a single base (`IRParentInstruction`)
* Dynamic casts to specific IR instruction types can be accomplished with a new `as<Type>(inst)` operation, that uses the IR opcode to implement casts.
The biggest change in terms of number of lines is getting rid of `IRValue`. The diff here could probably be smaller if I'd just done `typedef IRInst IRValue;`.
Along the way I also renamed the `getArg`/`getArgs`/`getArgCount` combination over to `getOperand`/`getOperands`/`getOperandCount` to avoid being confusing when we have something like a `call` instruction where the "arguments" of the call don't line up with the operands of the instruction.
I also tried to clean up the representation of lists of child instructions to try to make it easier to iterate over them with C++ range-based `for` loops. Developers still need to be careful about mutating the contents of a block while iterating over it in this fashion (e.g. if you remove the "current" element, the iteration will end prematurely).
Probably the thorniest change here is that parameters are now just represented as the first N instructions in a block, which means:
* We need to perform a linear search to find the end of the parameter list. This is probably not often a problem, because usually you would be iterating over the parameters anyway, and that will be linear in the number of parameters.
* Algorithms that iterate over a block either need to ignore parameters, treat parameters just like other instructions, or somehow cleave the list into the range of parameters, and the range of "ordinary" instructions (which involves the same linear search above).
* When inserting into a block, we need to be careful not to insert instructions at invalid locations (e.g., insert a temporary before the parameters, or insert a parameter in the middle of the code). I can't pretend that I've handled the details of that here. (This is no different than having to make the same adjustments for phi nodes in a typical SSA representation)
* One possible future-proof approach is to implement a pass that sorts the instructions in a block so that parameters always come first. That would let us implement passes without caring about this detail, and then clean up right before any pass that cares about the relative order of parameters and other instructions.
The current change is missing any work to make literals and other instructions that used to be `IRValue`s properly nest inside of their parent module. Right now these instructions are just left unparented, and may actually end up being shared between distinct modules. Fixing that will need a follow-up change. The biggest challenge there is that it introduces instructions at the global scope that aren't `IRGlobalValue`s.
This change doesn't try to take advantage of any of the new flexibility (e.g., by nesting `specialize` instructions inside of witness tables). The goal is to do exactly what we were doing before, just with a different representation.
* Warning fix
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* Initial work on validating "constexpr"-ness in IR
The underlying issue here is that certain operations in the target shading languages constrain their operands to be compile-time constants. A notable example is the optional texel offset parameter to the `Texture2D.Sample` operation.
When calling these operations in GLSL, the user is required to pass a "constant expression," and any variables in that expression must therefore be marked with the `const` qualifier (and themselves be initialized with constant expressions). Any GLSL output we generate must of course respect these rules.
When calling these operations in HLSL, the user is not so constrained. Instead, they can pass an arbitrary expression, which may involve ordinary variables with no particular markup, and then the compiler is responsible for determining if the actual value after simplification works out to be a constant. In some cases, the requirement that a value be constant might actually trigger things like loop unrolling. Also, it is okay to use a function parameter to determine such a constant expression, as long as the argument turns out to be a constant at all call sites.
The way we have decided to tackle these challenges in Slang is that we we propagate a notion of `constexpr`-ness through the IR. This is currently being tackled in `ir-constexpr.cpp` with a combination of forward and backward iterative dataflow:
* When the operands to an instruction are all `constexpr`, and the opcode is one we believe can be constant-folded, then we infer that the instruction *can* be evaluated as `constexpr`
* When instruction is required to be `constexpr`, then we infer that all of its operands are also required to be `constexpr`.
If this process ever infers that a function parameter is required to be `constexpr`, then we might have to continue propagation at all the call sites to that function.
If after all the propagation is done, there are any cases where an instruction is *required* to be `constexpr`, but it *can't* be `constexpr` (we weren't able to infer `constexpr`-ness for its operands), then we issue an error.
This implementation encodes the idea of `constexpr`-ness in the IR as part of the type system, using a simplified notion of rates. This change adds a `RateQualifiedType` that can represent `@R T`, and then introduces a `ConstExprRate` that can be used for `R`. Many accessors for the type information on IR nodes were updated to distinguish when one wants the "full" type of an IR value (which might include rate information) vs. just the "data" type.
A `constexpr` qualifier was added in the front-end, and is being used to decorate the texel offset parameter for `Texture2D.Sample`. Lowering from AST to IR looks for this qalifier and infers when a function parameter must be typed as `@ConstExpr T` instead of just `T`.
There are lots of limitations and gotchas in the implementation so far:
* The `@ConstExpr` rate is the only one added in this change, but it seems clear that the conceptual `ThreadGroup` rate that was added to represent `groupshared` should probably get folded into the representation.
* I'm not 100% pleased with how many places in the IR I have to special-case for rate-qualified types. At the same type, pulling out rate as a distinct field on `IRValue` would probably require that we pay attention to rate everywhere.
* I've added a test case to show that we can issue errors when users fail to provide a constant expression for the texel offset, but the actual error message isn't great because it doesn't indicate *why* a constant expression was required. Realistically the "initial IR" should contain a few more decorations we can use to relate error conditions back to the original code (even if this is in a side-band structure).
* I've added a test case that is supposed to show that we can back-propagate `constexpr`-ness to local variables, and I've manually confirmed that it works for Vulkan/SPIR-V output, but the level of Vulkan support in `render_test` today means I can't enable the test for check-in.
* While I'm attempting to propagate `@ConstExpr` information from callees to callers, I haven't implemented any logic to specialize callee functions based on values at call sites.
* In a similar vein, there is no handling of control-flow dependence in the current code. If we infer that a phi (block parameter) needs to be `@ConstExpr`, then it isn't actually enough to require that the inputs to the phi (arguments from predecessor blocks) are all `@ConstExpr` because we also need any control-flow decisions that pick which incoming edge we take to be `@ConstExpr` as well.
* As a practical matter, implicit propagation of `@ConstExpr` from a function body to a function parameter should only be allowed for functions that are "local" to a module. Any function that might be accessed from outside of a module should really have had its `@ConstExpr` parameter marked manually, and our pass should validate that they follow their own rules. Right now we have no kind of visibility (`public` vs `private`) system, so I'm kind of ignoring this issue.
While that is a lot of gaps, this is also just enough code to get the Falcor MultiPassPostProcess example working, so I'm inclined to get it checked in.
* Fixup: missing expected output for test
* Fixup: disable test that relies on [unroll] for now
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* Fix bugs around IR legalization of GLSL input/output
- Add case to handle assignment of one `ScalarizedVal::Flavor::address` to another (still need to make sure we are handling all the possible cases there)
- Revamp logic for creating global variable declarations for varying inputs/outputs.
- Actually handle creating array declarations (not sure if binding locations will be correct)
- Properly deal with offsetting of locations for nested fields
- Only create varying input/output layout information as needed for the separate `in` and `out` variables we create to represent a single HLSL `inout` varying
* During SSA generation, recursively remove trivial phis
This is actually written up in the original paper I used as a reference, but I hadn't implemented the case yet.
When you eliminate one phi as trivial (because its only operands were itself and at most one other value), you might find that another phi becomes trivial (because it had this phi as an operand, but now it will have the other value...).
The one thing that made any of this tricky is that our "phi" nodes are really block parameters, and thus they don't technically have operands (`IRUse`s). The `IRUse`s for each phi were being tracked in a separate array, and had their `user` field set to null.
With this change, I set their `user` to be the corresponding `IRParam` for the phi (and that means I changed `IRParam` to inherit from `IRUser` even though it shouldn't really be required).
* Re-build SSA form after specialization/legalization
The main reason to do this is that legalization might scalarize types, and thus might allow us to clean up resource-type local variables that we were not able to clean up when they were part of an aggregate.
Note: we shouldn't really need to do this, because the front-end should actually be guaranteeing that types that include resources are used in "safe" ways, but we currently don't have the analyses required to support that.
* Give an error message if we get GLSL input
The API and command-line interface still recognize and nominally support GLSL input files, because they need to be supported in the "pass-through" mode.
This change just adds an error message if we encounter a GLSL input file in anything other than "pass-through" mode.
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The basic problem here is that when unlinking an `IRUse` from the linked list of uses, there were several cases where I was failing to set the `prevLink` field of the next node to match the `prevLink` field of the node being removed. That doesn't show up when walking the linked list of uses forward, but it breaks it whenever you have subsequent unlinking operations.
This change fixes the bugs of that kind I could find, and also adds a debug validation method to try to avoid breaking it again. I also made more access to `IRUse` go through accessor methods rather than using fields directly, to try to avoid this kind of error. I stopped short of making anything `private`, because I tend to find that it creates more hassles than it avoids.
A few other fixes along the way:
- Made the `List<T>` type default-initialize elements when you resize it. I hadn't realized we weren't doing that.
- Add a standalone `dumpIR(IRGlobalValue*)` so help when debugging issues.
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* Basic IR support for `static const` globals
Our strategy for lowering global *variables* can fall back to putting their initialization into a function, but that isn't really appropriate for global constants (it also isn't appropriate for arrays, but we'll need to deal with that seaprately).
This change adds a distinct case for global constants (rather than treating them as variables), and forces the emission logic to always emit them as a single expression.
Doing this makes assumptions about how the IR for these constants gets emitted (and what optimziations might do to it).
In order to make things work, I had to switch the handling of initializer-list expressions to not be lowered via temporaries and mutation (since that isn't a good fit for reverting to a single expression).
I've added a single test case to ensure that this works in the simplest scenario. My next priority will be to see if this unblocks my work in Falcor.
* Fixup: bug fixes
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* Re-define deprecated compile flags
By including these flags in the header file, with a value of zero, we can allow some existing code to compile even after the major changes to the implementation.
* The `SLANG_COMPILE_FLAG_NO_CHECKING` option will effectively be ignored, since checking is always enabled.
* The `SLANG_COMPILE_FLAG_SPLIT_MIXED_TYPES` option will now act as if it is always enabled (and indeed some of the code has been relying on this flag being set always).
* Make subscript operators writable for writable textures
This even had a `TODO` comment saying that we needed to fix it, and now I'm seeing semantic checking failures because we didn't define these and so we find assignment to non l-values.
* Fix definitions of any() and all() intrinsics
These should always return a scalar `bool` value, but they were being defined wrong in two ways:
1. They were using their generic type parameter `T` in the return type
2. They were returning a vector in the vector case, and a matrix in the matrix case.
This change just alters the return type to be `bool` in all cases.
* Fix bug in SSA construction
When eliminating a trivial phi node, it is possible that the phi is still recorded as the "latest" value for a local variable in its block.
When later code queries that value from the block (which can happen whenever another block looks up a variable in its predecessors), it would get the old phi and not the replacement value.
I simply added a loop that checks if the value we look up is a phi that got replaced, and then continues with the replacement value (which might itself be a phi...). A more advanced solution might try to get clever and have the map itself hold `IRUse` values so that we can replace them seamlessly.
* Simplify IR control flow representation
This change gets rid of various special-case operations for conditional and unconditional branches, and instead requires emit logic to recognize when a direct branch is targetting a `break` or `continue` label.
The new approach here isn't perfect, but it seems beter than what we had before, because it can actually work in the presence of control-flow optimizations (including our current critical-edge-splitting step).
* Load from groupshared isn't groupshared
When loading from a `groupshared` variable, the resulting temporary shouldn't have the `groupshared` qualifier on it.
This might eventually need to generalize to a better understanding of storage modifiers in the IR, but I don't really want to deal with that right now.
* Don't emit references to typedefs in output code
Now that we are using the IR for all codegen, we shouldn't be dealing with surface-level things like `typedef` declarations in the output code; just use the type that was being referred to in the first place.
* Fix floating-point literal printing for IR
The IR was calling `emit()` instead of `Emit()` (we really need to normalize our convention here), and was implicitly invoking a default constructor on `String` that takes a `double` (that constructor should really be marked `explicit`), and which doesn't meet our requirements for printing floating-point values.
* Fix error when importing module that doesn't parse
We already added a case to bail out if semantic checking fails, but neglected to add a case if there is an error during parsing of a module to be imported.
Note: this logic doesn't correctly register the module as being loaded (but still in error), so users could see multiple error messages if there are multiple `import`s for the same module.
* Improve error message for overload resolution failure
- Drop debugging info from the candidate printing
- Add cases to print `double` and `half` types properly
* Fixup: switch loopTest to ifElse in expected IR output
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* Generate SSA form for IR functions
The basic idea here is simple: in the front-end after we have lowered the AST to initial IR we will apply a set of "mandatory" optimization passes. The first of these is to attempt to translate the all functions into SSA form so that they are amenable to subsequent dataflow optimizations. Eventually, the mandatory optimization passes would include diagnostic passes that make sure variables aren't used when undefined, etc.
Just doing basic SSA generation already cleans up a lot of the messiness in our IR today, because constructs that used to involve many local variables can now be handled via SSA temporaries.
The implementation of SSA generation is in `ir-ssa.cpp`, and it follows the approach of Braun et al.'s "Simple and Efficient Construction of Static Single Assignment Form." I used this instead of the more well-known Cytron et al. algorithm because Braun's algorith mis very simple to code, and does not require auxiliary analyses to generate the dominance frontier.
The main wrinkle in our SSA representation right now is that instead of using ordinary phi nodes, we instead allow basic blocks to have parameters, where predecessor blocks pass in different parameter values. This encodes information equivalent to traditional phi nodes, but has two (small) benefits:
1. There is no fixed relationship between the order of phi operands and predecessor blocks, so we don't have to worry about breaking the phis when we alter the order in which predecessors are stored. This is important for us because predecessors are being stored implicitly.
2. It is easy to operationalize a "branch with arguments" either when lowering to other languages, or when interpreting the IR. A branch with arguments is implemented as a sequence of stores from the arguments to the parameters of the target block (very similar to a call), followed by a jump to the block.
Relevant to the above, this change also adds an interface for enumerating the predecessors or successors of a block in our CFG. Rather than use an auxliary structure, we directly use the information already encoded in the IR:
* The sucessors of a block are the target label operands of its terminator instruction. In our IR this is a contiguous range of `IRUse`s, possible with a stride (to account for the way `switch` interleaves values and blocks).
* The predecessors of a block are a subset of the uses of the block's value. Specifically, they are any uses that are on a terminator instruction, and within the range of values that represent the successor list of that instruction.
One important limitation of the "blocks with arguments" model for handling phis is that it is really only convenient to stash extra arguments on an unconditional terminator instruction. This change works around this prob lem by breaking any "critical edges" - edges between a block with multiple successors and one with multiple predecessors. We assume that "phi" nodes will only ever be needed on a block with multiple predecessors, and because critical edges are broken, each of these predecessors will then have only a single successor, so its branch instruction can handle the extra arguments.
This change introduces a notion of an "undefined" instruction in the IR. This is handled as an instruction rather than a value because I anticipate that we will want to distinguish different undefined values when it comes time to start issuing error messages (those messages will need to point to the variable that was used when undefined).
* Fix expected test output.
Another change was merged that enabled the `glsl-parameter-blocks` test, and its output is affected by our IR optimization work.
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