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The code should now compile cleanly with warnings as errors for VS2015 with `W3`.
Most of the changes had to do with propagating a real pointer-sized integer type through code that had been using `int`.
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- The big change here is the introduction of a "lowering" pass that takes an input AST from the semantic checker, and produces an output AST suitable for emitting. The intention is that he lowering pass is responsible for:
- Stripping out unused code (when we have enough information to do so), by only outputting declarations that are transitively references from an entry point
- When cross-compiling to GLSL, generating a suitable `void main()` entry point to wrap the user-written entry-point function
- (Eventually) legalizing types in the program, by scalarizing aggregate types that mix uniform and resource types
- (Eventually) instantiating generic declarations so that the resulting code only deals with fully specialized declarations
- (Eventually) de-sugaring OOP constructs into basic "structs and functions" form
- (Eventually) instantiating code that depends on interface types at the concrete types chosen
- It is clear that there is still a lot of work to be done there, to this change is really about getting infrastructure in place without breaking the existing test cases.
- One cleanup here is that we get rid of the idea of whole-translation-unit output, since that was specific to HLSL output, and there is really no strong reason for keeping it. Users should now just ask for the output for each entry point that they wanted to generate.
- The biggest source of complexity for the lowering process is that it needs to produce the same AST structure as the input, to deal with the complexity of the rewriter case. That is, we need the output to be able to reproduce the input exactly in the case where we are rewriting and nothing needs to change, so the output format needs at least the degrees of freedom of the input.
- As a result, we end up having to distinguish "rewriter" and "full" modes in both lowering and code-emit steps, so that we can react appropriately.
- Generating a GLSL `main()` also adds a lot of complexity. Right now I'm using the simplest approach, where we always output the Slang/HLSL entry point as an ordinary function (as written) and then emit a simple GLSL `main()` to call it. I generate globals for all the shader inputs/outputs (these need to be scalarized and have explicit `location`s attached), and then collect these into the `struct` types of the original parameters as needed.
- This approach will start to have some major down-sides once we have to deal with "arrayed" input/output
- A long-term question here is how to replace entry-point parameter types with scalarized and/or "transposed" versions, while still letting the original code work as written (including copying those inputs to temporary arrays)
- Split `BlockStatementSyntaxNode` into:
- `BlockStmt` which just provides a scope around a `body` statement
- `SeqStmt` which just allows multiple statements to be treated as one
- Change how we emit `for` loops, to deal with the case where the initialization part might expand into multiple statements
- Basically `for(A;B;C) {D}` becomes `{A; for(;B;C) {D}}`, so we can handle arbitrary statements for `A`
- As an additional wrinkle, when we are rewriting HLSL, we just generate `A; for(;B;C) {D}` to deal with the broken scoping there
- This change is needed because the lowering pass was sometimes expanding the original initialization statement `A` into a block `{A}`. Certainly if it declared multiple variables we'd need to handle it, and this seemed the easiest way
- A more significant challenge for lowering would come if/when we ever wanted to support true short-circuiting behavior for `&&` and `||`
- For right now I'm not changing the behavior of the "rewriter" mode, so we still have `UnparsedStmt` instances being generated, but it is clear that eventually we need to parse *all* input, even if we can't type-check 100% of it. This is required so that we can rewrite user code that might refer to a shader input with interface type.
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The main user-visible change here is that instead of `spAddTranslationUnitEntryPoint` we have `spAddEntryPoint`, to reflect that the list of entry points is "global" to a compile request.
As a result, `spGetEntryPointSource` now only needs the entry point index, and not the translation unit index.
There are a bunch more behind-the-scenes changes, though, reflecting a streamlining of the concepts related to compilation into a smaller number of classes.
Now there is:
- `Session` (unchanged) to manage the lifetimes of shared stuff like the stdlib
- `CompileRequest` (merges in `CompileOptions`) to handle all the lifetime related to a single invocation of the compiler
- `TranslationUnitRequest` (merges `TranslationUnitOptions`, `CompileUnit`) to represent a single translation unit ("module") that the user is trying to compile. This is a single file for HLSL/GLSL, but can be multiple files for Slang.
- `EntryPointRequest` (merges `EntryPointOption` and a bit of `EntryPointResult`) to track a single entry point that the user is asking to compile (that entry point always comes from a single translation unit)
A lot of functions used to take some combination of these and end up with really long signatures.
I've given most of the objects "parent" pointers so that they can get back to all the context they need, so most functions don't need as many parameters.
It may eventually be important to tease these apart again, in particular:
- The code-generation side of things (the `*Result` types) might need to be pulled out in case we want to codegen multiple times from the same AST
- Similarly, the layout stuff may also need to be pulled out, in case we want to lay things out multiple times with different rules.
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The basic idea of this change is that user code can just write:
#include "foo.h"
and then if `foo.h` gets found in a list of registered directories for "auto-import," then it actually gets interpreted as if the user had writte, more or less:
__import foo;
That is, the code in `foo.h` will be treated as Slang, and will be fully parsed and checked (no matter what the source language had been), and the scoping rules will be those of `__import` instead of `#include`.
This is a really big hammer, and I could imagine it smashing fingers if used poorly.
I'm not sure this feature will pan out, but we need to try things to know.
One big piece of that that I'll likely keep in either case is an overhaul of command-line options parsing for `slangc`. In particular, this logic has been moved into the core `slang` library (so that users can just pass options in via the API), and it is all done on UTF-8 strings rather than wide strings (which was always going to be Windows-specific).
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This is a large change that contains many pieces:
- Update the `cross-compile0` test to actually make use of cross compilation.
Now the `cross-compile0.hlsl` file contains both HLSL and GLSL source code, and then imports code from `cross-compile0.slang`, which provides a "library" (one function) that can be shared between both the HLSL and GLSL version of things.
- Fixed a bug in the support for backslash-escaped newlines.
- Added a new `__import` declaration type (replaces the `using` directive that was still around in a vestigial form)
An `__import` causes the compiler to look for a Slang source file (currently using the ordinary `#include` lookup logic), and then parse/check the found file as an additional module ("translation unit"), before making its declarations visible in the current scope.
- Refactored the main compilation flow to be simpler. There were the `ShaderCompiler` and `ShaderCompilerImpl` classes that weren't relaly doing anything, but added complexity to the whole workflow.
- The `render-test` application has been heavily modified to better support testing cross-compilation workflows. At the most basic level we are starting to distinguish pass-through vs. rewriter workflows, and are passing various `#define`s down to the compiler(s) to let the source code be customized as needed for each case.
Several annoying corner cases are caused here by having to support the GLSL compilation model, which really wants each entry point in its own specific translation unit, whereas we really want to keep things nicely contained in single files.
- Added support for `__intrinsic` operations to have target-specific behavior.
This allows a function to be given a different name for some specific target (so a call gets emitted as a call to that other operation).
More generally, the library writer can put together an arbitrary format string that will be used in place of expressions that call the given function, e.g.:
__intrinsic(hlsl, "$1 - $0") __intrinsic int foo(int a, int b);
Given this declaration, a call like `foo(x,y)` will code generate as `x - y` for HLSL, and as `foo(x,y)` for all other targets.
Annoying things still to be dealt with:
- The way that I'm filtering the user-provided options when passing things down to the compilation of dynamically loaded modules is a bit ad hoc. It would be good to have a systematic notion of which options will be inherited and which won't. There is also more code duplication than I'd like, so we risk having the compiler behave differently when compiling a file at the top level, vs. because of `__import`.
- Adding target-specific behavior to intrinsics is all well and good, but the current approach means we can only add this to the original declaration, which limits the ability to easily extend the set of targets.
A better approach long-term would be to add a more robust notion of target-based overload resolution (which would happen after semantic checking). Then one mechanism would be used to find the right target-specific overload to use for an operation, and then each (target-specific) definition could use a simpler attribute to intercept code-generation behavior.
Note that we might eventually need a similar notion to deal with stage- or profile-specific functions and the overloading behavior around them, so using this for intrinsics doesn't seem like a bad idea.
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The test case that is there right now is nominally a cross-compilation test, but for right now it uses the preprocessor to present completely different code for HLSL and GLSL compilation.
This change is really just fleshing out the OpenGL side of `render-test` enough that it can produce images using OpenGL to enable further testing.
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