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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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