[HLSL] Infer language from file extension

This allows the language mode for HLSL to be inferred from the file
extension.

clang/lib/Frontend/FrontendOptions.cpp

@@ -33,5 +33,6 @@ InputKind FrontendOptions::getInputKindForExtension(StringRef Extension) {
       .Cases("cu", "cuh", Language::CUDA)
       .Case("hip", Language::HIP)
       .Cases("ll", "bc", Language::LLVM_IR)
+      .Case("hlsl", Language::HLSL)
       .Default(Language::Unknown);
 }

clang/test/Preprocessor/predefined-macros-hlsl.hlsl

@@ -0,0 +1,48 @@
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-amplification | FileCheck -match-full-lines %s --check-prefixes=CHECK,AMPLIFICATION
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-compute | FileCheck -match-full-lines %s --check-prefixes=CHECK,COMPUTE
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-domain | FileCheck -match-full-lines %s --check-prefixes=CHECK,DOMAIN
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-geometry | FileCheck -match-full-lines %s --check-prefixes=CHECK,GEOMETRY
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-hull | FileCheck -match-full-lines %s --check-prefixes=CHECK,HULL
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-library | FileCheck -match-full-lines %s --check-prefixes=CHECK,LIBRARY
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-mesh | FileCheck -match-full-lines %s --check-prefixes=CHECK,MESH
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-pixel | FileCheck -match-full-lines %s --check-prefixes=CHECK,PIXEL
+// RUN: %clang_cc1 %s -E -dM -o - -triple dxil-pc-shadermodel6.0-vertex | FileCheck -match-full-lines %s --check-prefixes=CHECK,VERTEX
+
+// CHECK: #define __HLSL_VERSION 2021
+// CHECK: #define __SHADER_STAGE_AMPLIFICATION 14
+// CHECK: #define __SHADER_STAGE_COMPUTE 5
+// CHECK: #define __SHADER_STAGE_DOMAIN 4
+// CHECK: #define __SHADER_STAGE_GEOMETRY 2
+// CHECK: #define __SHADER_STAGE_HULL 3
+// CHECK: #define __SHADER_STAGE_LIBRARY 6
+// CHECK: #define __SHADER_STAGE_MESH 13
+// CHECK: #define __SHADER_STAGE_PIXEL 0
+// CHECK: #define __SHADER_STAGE_VERTEX 1
+
+// AMPLIFICATION: #define __SHADER_TARGET_STAGE 14
+// COMPUTE: #define __SHADER_TARGET_STAGE 5
+// DOMAIN: #define __SHADER_TARGET_STAGE 4
+// GEOMETRY: #define __SHADER_TARGET_STAGE 2
+// HULL: #define __SHADER_TARGET_STAGE 3
+// LIBRARY: #define __SHADER_TARGET_STAGE 6
+// MESH: #define __SHADER_TARGET_STAGE 13
+// PIXEL: #define __SHADER_TARGET_STAGE 0
+// VERTEX: #define __SHADER_TARGET_STAGE 1
+
+// RUN: %clang_cc1 %s -E -dM -o - -std=hlsl2015 | FileCheck -match-full-lines %s --check-prefixes=STD2015
+// STD2015: #define __HLSL_VERSION 2015
+
+// RUN: %clang_cc1 %s -E -dM -o - -std=hlsl2016 | FileCheck -match-full-lines %s --check-prefixes=STD2016
+// STD2016: #define __HLSL_VERSION 2016
+
+// RUN: %clang_cc1 %s -E -dM -o - -std=hlsl2017 | FileCheck -match-full-lines %s --check-prefixes=STD2017
+// STD2017: #define __HLSL_VERSION 2017
+
+// RUN: %clang_cc1 %s -E -dM -o - -std=hlsl2018 | FileCheck -match-full-lines %s --check-prefixes=STD2018
+// STD2018: #define __HLSL_VERSION 2018
+
+// RUN: %clang_cc1 %s -E -dM -o - -std=hlsl2021 | FileCheck -match-full-lines %s --check-prefixes=STD2021
+// STD2021: #define __HLSL_VERSION 2021
+
+// RUN: %clang_cc1 %s -E -dM -o - -std=hlsl202x | FileCheck -match-full-lines %s --check-prefixes=STD202x
+// STD202x: #define __HLSL_VERSION 2029