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Initial WGSL support (shader-slang#5006)
* Add WGSL as a target This is required for shader-slang#4807. * C-like emitter: Allow the function header emission to be overloaded WGSL-style function headers are pretty different from normal C-style headers: Normal C-style headers: ReturnType Func(...) void VoidFunc(...) WGSL-style headers: fn Func(...) -> ReturnType fn VoidFunc(...) This change allows the header style to be overloaded, in order to accomodate WGSL-style headers as required to resolve issue shader-slang#4807, but retains normal C-style headers as the default implementation. [1] https://www.w3.org/TR/WGSL/#function-declaration-sec * C-like emitter: Allow emission of switch case selectors to be overloaded The C-like emitter will emit code like this: switch(a.x) { case 0: case 1: { ... } break; ... } This is not allowed in WGSL. Instead, selectors for cases that share a body must [1] be separated by commas, like this: switch(a.x) { case 0, 1: { ... } break; ... } To prepare for addressing issue shader-slang#4807, this patch makes the emission of switch case selectors overloadable. [1] https://www.w3.org/TR/WGSL/#syntax-case_selectors * C-like emitter: Support WGSL-style declarations This patch helps to address issue 4807. C-like languages declare variables like this: i32 a; WGSL declares variables like this: var a : i32 The patch introduces overloads so that the forthcoming WGSL emitter can output WGSL-style declarations, which helps to resolve shader-slang#4807. * C-like emitter: Support overloading of declarators Unlike C-like languages, WGSL does not support the following types at the syntax level, via declarators: - arrays - pointers - references For this reason, this patch introduces support for overloading the declarator emitter, in order to help address issue shader-slang#4807. C-like languages: int a[3]; // Array-ness of type is mixed into the "declarator" WGSL: var a : array<int, 3>; // Array-ness of type is part of the... type_specifier! * C-like emitter: Allow struct declaration separator to be overridden C-like languages use ';' as a separator, and languages like e.g. WGSL use ','. This change prepares for addressing issue shader-slang#4807. * C-like emitter: Allow overriding of whether pointer-like syntax is necessary Things like e.g. structured buffers map to "ptr-to-array" in WGSL, but ptr-typed expressions don't always need C-style pointer-like syntax. Therefore, make it overrideable whether or not such syntax is emitted in various cases in order to address shader-slang#4807. * C-like emitter: Emit parenthesis to avoid warning about & and + precedence This helps with shader-slang#4807 because WGSL compilers (e.g. Tint) treat absence of parenthesis as an error. * C-like emitter: Add hook for emitting struct field attributes WGSL requires @align attributes to specify explicit field alignment in certain cases. Thus, this patch prepares for addressing shader-slang#4807. * C-like emitter: Add hook for emitting global param types Declarations of structured buffers map to global array declarations in WGSL. However, in all other cases such as when structured buffers are used in operands, their types map to *ptr*-to-array. This patch makes it possible for the WGSL back-end to say that structured buffers generally map to "ptr-to-array" types, but still have a special case of just "array" when declaring the global shader parameter. Thus, this patch helps with addressing shader-slang#4807. * IR lowering: Use std140 for WGSL uniform buffers This patch just cuts out some logic that prevented std140 to be chosen for WGSL uniform buffers. Note that WGSL buffers in the uniform address space is not quite std140, but for now it's close enough to avoid compile issues. Later on, a custom layout should be created for WGSL uniform buffers. When that's done, this change will be revisited, but for now it helps to resolve shader-slang#4807. * Don't emit line directives in WGSL by default WGSL does not support line directives [1]. The plan currently seems to be to instead support source-map [2]. This is part of addressing issue shader-slang#4807. [1] gpuweb/gpuweb#606 [2] https://github.com/mozilla/source-map * WGSL IR legalization: Map SV's The implementation closely follows the cooresponding one for Metal. Supported: - DispatchThreadID - GroupID - GroupThreadID - GroupThreadID Unsupported: - GSInstanceID This is not complete, but it helps to address shader-slang#4807. * WGSL emitter: Add support for basic language constructs A lot of the basics are added in order to generate correct WGSL code for basic Slang language constructs. This addresses issue shader-slang#4807. This adds support for at least the following: - statments - if statements - ternary operator - while statement - for statements - variable declarations - switch statements - Note: Slang may emit non-constant case expressions, see issue 4834 - literals - integer literals - u?int[16|32|64]_t - float and half literals - bool literals - vector literals and splatting (e.g 1.xxx) - function definitions - assignments - +=, *=, /= - array assignments - vector assignments/updates - swizzles of other vectors - from matrix rows ('m[i]' notation) - from matrix cols (using swizzle notation, e.g 'm._11_12_13') - matrix assignments/updates - to rows ('m[i]' notation) - to cols (using swizzle notation, e.g 'm._11_12_13') - declarations - arrays [1] https://www.w3.org/TR/WGSL/#syntax-switch_body * Add some WGSL capabilities This patch registers some WGSL capabilities required to pass many of the initial compute shader compile tests. Many capabilities still remain to be added -- this is just an initial set to help resolve issue shader-slang#4807. - asint - min and max - cos and sin - all and any * WGSL and C-like emitters: Add hack to bitcast case expression In WGSL, the switch condition and case types must match. https://www.w3.org/TR/WGSL/#switch-statement Slang currently allows these types to mismatch, as pointed out in shader-slang#4921. Issue shader-slang#4921 should eventually be addressed in the front-end by a patch like [1]. However, at the moment that would break Falcor tests. Thus, this patch temporarily works around the issue in the WGSL emitter only in order to help resolve shader-slang#4807. In the future, the Falcor tests should be fixed, this patch should be dropped and [1] should be merged instead. [1] a32156e
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