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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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The basic change is simple: remove support for all code generation paths other than the IR.
There is a lot of vestigial code left, but the main logic in `ast-legalize.*` is gone.
Doing this breaks a *lot* of tests, for various reasons:
- We can no longer guarantee exactly matching DXBC or SPIR-V output after things pass through out IR
- Many builtins don't have matching versions defined for GLSL output via IR (even when they had versions defined via the earlier approach that worked with the AST)
- A lot of code creates intermediate values of opaque types in the IR, which turn into opaque-type temporaries that aren't allowed (this breaks many GLSL tests, but also some HLSL)
I implemented some small fixes for issues that I could get working in the time I had, but most of the above are larger than made sense to fix in this commit.
For now I'm disabling the tests that cause problems, but we will need to make a concerted effort to get things working on this new substrate if we are going to make good on our goals.
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* Bug fix: emit logic for `do` loops
This case was never tested, and I was outputting some garbage characters. This comit fixes the codegen and adds a test case.
* Bug fix: make sure to pass through `[allow_uav_condition]`
This also fixes the standard library definition of `IncrementCounter()` so that it returns a `uint` instead of `void`.
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The main change I was working on here was to start having more of the builtin functions (in this case, `cos`, `sin`, and `saturate`) just lower to the IR as calls to builtin functions (with declarations but no definition), rather than expect/require them to map to individual IR opcodes in every case.
The main change there was the removal of some `intrinsic_op` modifiers in the stdlib. This then requires the `isTargetInstrinsic` logic in IR-based code emit to avoid emitting declarations for these intrinsics.
The corresponding logic for emitting *calls* to these intrinsics is currently being skipped.
Along the way, a variety of fixups were added:
- In order to support lowering to GLSL, we need to handle cases where a variable/function name uses a GLSL reserved word. The right long-term fix there is to always use generated or mangled names, but for now I'm hacking it by adding a `_s` prefix to all names during IR-based emit.
- This needs a flag to disable it, since some of our tests currently rely on checking binding information from generated HLSL/SPIR-V that will include these mangled/modified names.
- Emit matrix layout modifiers appropriately for GLSL
- Specialize IR parameter-block emission between GLSL and HLSL
- Fix up argument count/index logic for a couple of opcodes that weren't fixed when removing the types from the explicit operand list
- Fix up IR generation for calls to declarations with generic arguments. We were briefly adding the generic args to the ordinary argument list, which added complexity in several places. We now rely on the declaration-reference nodes in the IR to carry that extra info.
- TODO: We actually need to make sure that this is the case, since we don't currently correctly generated specialized decl-refs when building IR for function calls
The main test that would have been affected by this is `cross-compile-entry-point`, but I was not able to get that working fully with the IR. The main problem in this case was that when emitting GLSL we will need to perform certain required transformations on the IR to get legal code for GLSL. Notably:
- We need to hoist entry-point parameters away from being function parameters, and make them be global variables. This is currently being hand-waved during the emit logic, but it seems way better to have it all get cleaned up in the IR first.
- We need to scalarize entry-point parameters, because structure input/output is not supported as vertex input or fragment output (and it may be best to always scalarize anyway, to match HLSL semantics). (Note: "scalarize" here means to bust up structures, but not matrices/vectors)
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I had expected this to be the first case where control-flow instructions were needed, but it turns out that we aren't testing that entry point right now.
The real work/fix here ended up being handling of the `row_major` layout qualifier on a matrix inside a `cbuffer`. The existing AST-based code was passing it through easily (although I don't believe it was handling the layout rules right).
Getting it working in the IR involved beefing up the type-layout behavior so that it can handle explicit layout qualifiers (at least for matrix layout) which should also improve the layout computation for non-square matrices with nonstandard layout in the AST-based path.
There are still some annoying things left to do:
- The `row_major` and `column_major` layout qualifiers in HLSL/GLSL mean different things (well, they mean the reverse of one another) so I need to validate that the GLSL case is working remotely correctly.
- The layout logic isn't handling other explicit-layout cases as supported by GLSL (but of course GLSL is a far lower priority than HLSL/Slang)
- There is currently no way to pass in an explicit matrix layout flag to Slang to control the default behavior.
- Any client who was using Slang for HLSL pass-through and then applying a non-default flag on their HLSL->* compilation will get nasty unexpected behavior when the IR goes live - and they are already dealing with nasty behavior around non-square matrices not matching layout between Slang and the downstream.
- The logic that gleans layout modes from a variable declaration is currently only being applied for fields of structure types (which applies to `cbuffer` declarations as well), and not to global-scope uniform variables.
- We need test cases for all of this.
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This at least tries to capture some of the basic rules about what implicit conversions are allowed.
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- Add logic to extract the value and suffix from a numeric literal
- This duplicates some of the lexing logic, but this is hard to avoid without redundant runtime work
- Note that I'm not using and stdlib string-to-number code. This should be more robust once it is working, but it is obviously error prone in the near term. The main up-sides to this are:
- We can handle binary integer literals
- We can handle hexadecimal floating-point literals without stdlib support
- We can hypothetically support digit separators, if we ever wanted
- The parser looks at the suffix characters sliced off by the lexer, and tries to pick a type to use for a literal
- It uses `NULL` if there is no suffix, to avoid some nasty order dependencies where the stdlib might need to parse a number before it has seen the definition of `int`
- Right now I only handle a few cases, so there may be bugs lurking here
- The emit logic needs to handle the fact that a literal node in the AST might have a non-default type attached.
- Right now I just quickly check for the most likely types, and emit the literal with a matching suffix. This doesn't seem robust if any source language supports a suffix for a type where a target has no corresponding suffix. In the long term some amount of casting is probably required.
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String literals can be used as part of attributes, but we lacked an actual AST representation for them.
This change adds basic parsing for string literals, as well as emit logic for them.
I also included a fix for parsing of chained right-associative operators.
To test these fixes, I've re-enabled one of the HLSL tests I disabled a while back. It would be good to go through and see how many of those we can re-enable now.
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This includes a bunch of related changes:
- `slang-test`
- Add a notion of an "output mode" that specifies whether we output to console (the default), or invoke the apprpriate AppVeyor command to update test status
- Add a notion of test categories, so that tests can be tagged with categories, and then we can invoke only those tets in a given category, or choose to *exclude* tests with specific categories
- Allow the `OSProcessSpawner` to look up an executable by "path" (meaning a full path is expected) or by "name" (meaning it should be allowed to look in the current directory, `PATH` environment variable, etc.). This was important to make sure that I can run `appveyor` without having to know its absolute path.
- AppVeyor configuration
- Change badge to reflect new build account for organization (rather than a single-user account)
- Remove attempt to set AppVeyor build version in a clever way, since it breaks links from GitHub to AppVeyor
- Change order or configurations in the build matrix to front-load the Release build (which has the main tests)
- Turn on `fast_finish` flag so we don't have to wait as long for failed builds
- Turn on `parallel` builds
- Set `verbosity: minimal` to avoid getting build spew about Xamarin stuff I'm not using
- Add custom `test_script` to invoke `test.bat`
- Sets the test category based on teh build configuration, so we don't run the full test suite on every input.
- `test.bat`
- Allow for `-platform` and `-configuration` arguments
- Rewrute a platform of `Win32` over to `x86` to match how the output directories are named
- Futz around with how the directories are being passed along to work around annoying `.bat` file quoting behavior (I still don't get how batch files work)
- Tests
- Mark a bunch of tests as `smoke` tests
- Mark the relevant tests as `render` tests
(these get filtered out for AppVeyor builds)
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