Author: Chris B Date: 2024-03-20T10:16:17-05:00 New Revision: 48a1a9b26048d2a88eaf5b09de0525ab557615de
URL: https://github.com/llvm/llvm-project/commit/48a1a9b26048d2a88eaf5b09de0525ab557615de DIFF: https://github.com/llvm/llvm-project/commit/48a1a9b26048d2a88eaf5b09de0525ab557615de.diff LOG: [HLSL][docs] Document hlsl.h in the HLSL docs (#84081) This adds a brief blurb about hlsl.h in the HLSLSupport documentation where a high level view of the architecture is explained. Added: Modified: clang/docs/HLSL/HLSLSupport.rst Removed: ################################################################################ diff --git a/clang/docs/HLSL/HLSLSupport.rst b/clang/docs/HLSL/HLSLSupport.rst index b091c17fd2a764..2d309ddff2f36a 100644 --- a/clang/docs/HLSL/HLSLSupport.rst +++ b/clang/docs/HLSL/HLSLSupport.rst @@ -91,7 +91,7 @@ performance win for HLSL. If precompiled headers are used when compiling HLSL, the ``ExternalSemaSource`` will be a ``MultiplexExternalSemaSource`` which includes both the ``ASTReader`` -and ``HLSLExternalSemaSource``. For Built-in declarations that are already +and -. For Built-in declarations that are already completed in the serialized AST, the ``HLSLExternalSemaSource`` will reuse the existing declarations and not introduce new declarations. If the built-in types are not completed in the serialized AST, the ``HLSLExternalSemaSource`` will @@ -114,6 +114,54 @@ not re-targetable, we want to share the Clang CodeGen implementation for HLSL with other GPU graphics targets like SPIR-V and possibly other GPU and even CPU targets. +hlsl.h +------ + +HLSL has a library of standalone functions. This is similar to OpenCL and CUDA, +and is analogous to C's standard library. The implementation approach for the +HLSL library functionality draws from patterns in use by OpenCL and other Clang +resource headers. All of the clang resource headers are part of the +``ClangHeaders`` component found in the source tree under +`clang/lib/Headers <https://github.com/llvm/llvm-project/tree/main/clang/lib/Headers>`_. + +.. note:: + + HLSL's complex data types are not defined in HLSL's header because many of + the semantics of those data types cannot be expressed in HLSL due to missing + language features. Data types that can't be expressed in HLSL are defined in + code in the ``HLSLExternalSemaSource``. + +Similar to OpenCL, the HLSL library functionality is implicitly declared in +translation units without needing to include a header to provide declarations. +In Clang this is handled by making ``hlsl.h`` an implicitly included header +distributed as part of the Clang resource directory. + +Similar to OpenCL, HLSL's implicit header will explicitly declare all overloads, +and each overload will map to a corresponding ``__builtin*`` compiler intrinsic +that is handled in ClangCodeGen. CUDA uses a similar pattern although many CUDA +functions have full definitions in the included headers which in turn call +corresponding ``__builtin*`` compiler intrinsics. By not having bodies HLSL +avoids the need for the inliner to clean up and inline large numbers of small +library functions. + +HLSL's implicit headers also define some of HLSL's typedefs. This is consistent +with how the AVX vector header is implemented. + +Concerns have been expressed that this approach may result in slower compile +times than the approach DXC uses where library functions are treated more like +Clang ``__builtin*`` intrinsics. No real world use cases have been identified +where parsing is a significant compile-time overhead, but the HLSL implicit +headers can be compiled into a module for performance if needed. + +Further, by treating these as functions rather than ``__builtin*`` compiler +intrinsics, the language behaviors are more consistent and aligned with user +expectation because normal overload resolution rules and implicit conversions +apply as expected. + +It is a feature of this design that clangd-powered "go to declaration" for +library functions will jump to a valid header declaration and all overloads will +be user readable. + HLSL Language ============= _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
