[HLSL][SPIR-V] Implement vk::ext_builtin_input attribute (#138530)

This variable attribute is used in HLSL to add Vulkan specific builtins
in a shader.
The attribute is documented here:

https://github.com/microsoft/hlsl-specs/blob/17727e88fd1cb09013cb3a144110826af05f4dd5/proposals/0011-inline-spirv.md

Those variable, even if marked as `static` are externally initialized by
the pipeline/driver/GPU. This is handled by moving them to a specific
address space `hlsl_input`, also added by this commit.

The design for input variables in Clang can be found here:
https://github.com/llvm/wg-hlsl/blob/355771361ef69259fef39a65caef8bff9cb4046d/proposals/0019-spirv-input-builtin.md


Co-authored-by: Justin Bogner <mail@justinbogner.com>

Author: Keenuts

clang/include/clang/Basic/AddressSpaces.h

@@ -61,6 +61,7 @@ enum class LangAS : unsigned {
   hlsl_constant,
   hlsl_private,
   hlsl_device,
+  hlsl_input,
 
   // Wasm specific address spaces.
   wasm_funcref,

clang/include/clang/Basic/Attr.td

@@ -140,6 +140,12 @@ def SharedVar : SubsetSubject<Var,
                               [{S->hasGlobalStorage() && !S->getTLSKind()}],
                               "global variables">;
 
+def HLSLInputBuiltin
+    : SubsetSubject<Var, [{S->hasGlobalStorage() &&
+                           S->getStorageClass() == StorageClass::SC_Static &&
+                           S->getType().isConstQualified()}],
+                    "static const globals">;
+
 def GlobalVar : SubsetSubject<Var,
                              [{S->hasGlobalStorage()}], "global variables">;
 
@@ -4951,6 +4957,14 @@ def HLSLWaveSize: InheritableAttr {
   let Documentation = [WaveSizeDocs];
 }
 
+def HLSLVkExtBuiltinInput : InheritableAttr {
+  let Spellings = [CXX11<"vk", "ext_builtin_input">];
+  let Args = [UnsignedArgument<"BuiltIn">];
+  let Subjects = SubjectList<[HLSLInputBuiltin], ErrorDiag>;
+  let LangOpts = [HLSL];
+  let Documentation = [HLSLVkExtBuiltinInputDocs];
+}
+
 def RandomizeLayout : InheritableAttr {
   let Spellings = [GCC<"randomize_layout">];
   let Subjects = SubjectList<[Record]>;

clang/include/clang/Basic/AttrDocs.td

@@ -8508,6 +8508,29 @@ and copied back to the argument after the callee returns.
   }];
 }
 
+def HLSLVkExtBuiltinInputDocs : Documentation {
+  let Category = DocCatVariable;
+  let Content = [{
+Vulkan shaders have `Input` builtins. Those variables are externally
+initialized by the driver/pipeline, but each copy is private to the current
+lane.
+
+Those builtins can be declared using the `[[vk::ext_builtin_input]]` attribute
+like follows:
+
+.. code-block:: c++
+
+  [[vk::ext_builtin_input(/* WorkgroupId */ 26)]]
+  static const uint3 groupid;
+
+This variable will be lowered into a module-level variable, with the `Input`
+storage class, and the `BuiltIn 26` decoration.
+
+The full documentation for this inline SPIR-V attribute can be found here:
+https://github.com/microsoft/hlsl-specs/blob/main/proposals/0011-inline-spirv.md
+  }];
+}
+
 def AnnotateTypeDocs : Documentation {
   let Category = DocCatType;
   let Heading = "annotate_type";

clang/include/clang/Basic/AttributeCommonInfo.h

@@ -69,7 +69,7 @@ class AttributeCommonInfo {
     IgnoredAttribute,
     UnknownAttribute,
   };
-  enum class Scope { NONE, CLANG, GNU, MSVC, OMP, HLSL, GSL, RISCV };
+  enum class Scope { NONE, CLANG, GNU, MSVC, OMP, HLSL, VK, GSL, RISCV };
   enum class AttrArgsInfo {
     None,
     Optional,

clang/include/clang/Sema/SemaHLSL.h

@@ -131,6 +131,8 @@ class SemaHLSL : public SemaBase {
   void handleParamModifierAttr(Decl *D, const ParsedAttr &AL);
   bool handleResourceTypeAttr(QualType T, const ParsedAttr &AL);
 
+  void handleVkExtBuiltinInputAttr(Decl *D, const ParsedAttr &AL);
+
   bool CheckBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall);
   QualType ProcessResourceTypeAttributes(QualType Wrapped);
   HLSLAttributedResourceLocInfo

clang/lib/AST/Type.cpp

@@ -100,6 +100,7 @@ bool Qualifiers::isTargetAddressSpaceSupersetOf(LangAS A, LangAS B,
          // address spaces to default to work around this problem.
          (A == LangAS::Default && B == LangAS::hlsl_private) ||
          (A == LangAS::Default && B == LangAS::hlsl_device) ||
+         (A == LangAS::Default && B == LangAS::hlsl_input) ||
          // Conversions from target specific address spaces may be legal
          // depending on the target information.
          Ctx.getTargetInfo().isAddressSpaceSupersetOf(A, B);

clang/lib/AST/TypePrinter.cpp

@@ -2667,6 +2667,8 @@ std::string Qualifiers::getAddrSpaceAsString(LangAS AS) {
     return "hlsl_private";
   case LangAS::hlsl_device:
     return "hlsl_device";
+  case LangAS::hlsl_input:
+    return "hlsl_input";
   case LangAS::wasm_funcref:
     return "__funcref";
   default:

clang/lib/Basic/Attributes.cpp

@@ -210,6 +210,7 @@ getScopeFromNormalizedScopeName(StringRef ScopeName) {
       .Case("gnu", AttributeCommonInfo::Scope::GNU)
       .Case("gsl", AttributeCommonInfo::Scope::GSL)
       .Case("hlsl", AttributeCommonInfo::Scope::HLSL)
+      .Case("vk", AttributeCommonInfo::Scope::VK)
       .Case("msvc", AttributeCommonInfo::Scope::MSVC)
       .Case("omp", AttributeCommonInfo::Scope::OMP)
       .Case("riscv", AttributeCommonInfo::Scope::RISCV);

clang/lib/Basic/TargetInfo.cpp

@@ -49,6 +49,8 @@ static const LangASMap FakeAddrSpaceMap = {
     13, // hlsl_groupshared
     14, // hlsl_constant
     15, // hlsl_private
+    16, // hlsl_device
+    17, // hlsl_input
     20, // wasm_funcref
 };
 

clang/lib/Basic/Targets/AArch64.h

@@ -47,6 +47,7 @@ static const unsigned ARM64AddrSpaceMap[] = {
     0, // hlsl_constant
     0, // hlsl_private
     0, // hlsl_device
+    0, // hlsl_input
     // Wasm address space values for this target are dummy values,
     // as it is only enabled for Wasm targets.
     20, // wasm_funcref