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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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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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