[HLSL] Change default linkage of HLSL functions to internal (#95331)

An HLSL function has internal linkage by default unless it is:
1. shader entry point function
2. marked with the `export` keyword
(https://github.com/llvm/llvm-project/issues/92812)
3. patch constant function (not implemented yet)

This PR adds a link-time pass `DXILFinalizeLinkage` that updates the
linkage of functions to make sure only shader entry points and exported
functions are visible from the module (have _program linkage_). All
other functions will be updated to have internal linkage.

Related spec update: microsoft/hlsl-specs#295

Fixes #llvm/llvm-project#92071

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/Target/DirectX/DirectXTargetMachine.cpp b/llvm/lib/Target/DirectX/DirectXTargetMachine.cpp
index 92bd69b..2c2b86e 100644
--- a/llvm/lib/Target/DirectX/DirectXTargetMachine.cpp
+++ b/llvm/lib/Target/DirectX/DirectXTargetMachine.cpp
@@ -48,6 +48,7 @@ extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeDirectXTarget() {
   initializeDXILTranslateMetadataPass(*PR);
   initializeDXILResourceMDWrapperPass(*PR);
   initializeShaderFlagsAnalysisWrapperPass(*PR);
+  initializeDXILFinalizeLinkageLegacyPass(*PR);
 }
 
 class DXILTargetObjectFile : public TargetLoweringObjectFile {
@@ -79,6 +80,7 @@ public:
   void addCodeGenPrepare() override {
     addPass(createDXILIntrinsicExpansionLegacyPass());
     addPass(createDXILOpLoweringLegacyPass());
+    addPass(createDXILFinalizeLinkageLegacyPass());
     addPass(createDXILTranslateMetadataPass());
     addPass(createDXILPrepareModulePass());
   }