[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>

1 files changed, 17 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 9383c57..468fc6e 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -5763,7 +5763,17 @@ void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D,
     getCUDARuntime().handleVarRegistration(D, *GV);
   }
 
-  GV->setInitializer(Init);
+  if (LangOpts.HLSL && GetGlobalVarAddressSpace(D) == LangAS::hlsl_input) {
+    // HLSL Input variables are considered to be set by the driver/pipeline, but
+    // only visible to a single thread/wave.
+    GV->setExternallyInitialized(true);
+  } else {
+    GV->setInitializer(Init);
+  }
+
+  if (LangOpts.HLSL)
+    getHLSLRuntime().handleGlobalVarDefinition(D, GV);
+
   if (emitter)
     emitter->finalize(GV);
 
@@ -5806,6 +5816,12 @@ void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D,
       !D->hasAttr<ConstInitAttr>())
     Linkage = llvm::GlobalValue::InternalLinkage;
 
+  // HLSL variables in the input address space maps like memory-mapped
+  // variables. Even if they are 'static', they are externally initialized and
+  // read/write by the hardware/driver/pipeline.
+  if (LangOpts.HLSL && GetGlobalVarAddressSpace(D) == LangAS::hlsl_input)
+    Linkage = llvm::GlobalValue::ExternalLinkage;
+
   GV->setLinkage(Linkage);
   if (D->hasAttr<DLLImportAttr>())
     GV->setDLLStorageClass(llvm::GlobalVariable::DLLImportStorageClass);