[clang] [HLSL] Change default linkage of HLSL functions and groupshared variables (v2) (PR #95331)

[Chris B via cfe-commits]

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@@ -664,11 +664,25 @@ LinkageComputer::getLVForNamespaceScopeDecl(const NamedDecl *D,
       if (PrevVar->getStorageClass() == SC_Static)
         return LinkageInfo::internal();
     }
+
+    if (Context.getLangOpts().HLSL &&
+        Var->hasAttr<HLSLGroupSharedAddressSpaceAttr>())
+      return LinkageInfo::internal();
+
   } else if (const auto *IFD = dyn_cast<IndirectFieldDecl>(D)) {
     //   - a data member of an anonymous union.
     const VarDecl *VD = IFD->getVarDecl();
     assert(VD && "Expected a VarDecl in this IndirectFieldDecl!");
     return getLVForNamespaceScopeDecl(VD, computation, IgnoreVarTypeLinkage);
+
+  } else if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
+    // HLSL: Functions that are not exported library functions have internal
+    // linkage by default. That includes shader entry point functions, which
+    // will be wrapped by an external linkage function with unmangled C-style
+    // name during CodeGen.
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llvm-beanz wrote:

I don't think this is the behavior we want. It isn't just an issue for library functions, this also becomes an issue when we think about multi-translation unit building (DXC's lib_6_x profile). We really do want to match C++'s rules for external functions.

What we need to do differently is when targeting a known specific profile we can skip emitting unused declarations.

https://github.com/llvm/llvm-project/pull/95331