[llvm-branch-commits] [clang] [HLSL] Introduce address space `hlsl_constant(2)` for constant buffer declarations (PR #123411)

[Helena Kotas via llvm-branch-commits]

================
@@ -455,14 +456,22 @@ void createHostLayoutStructForBuffer(Sema &S, HLSLBufferDecl *BufDecl) {
   LS->setImplicit(true);
   LS->startDefinition();
 
-  for (const Decl *D : BufDecl->decls()) {
-    const VarDecl *VD = dyn_cast<VarDecl>(D);
+  for (Decl *D : BufDecl->decls()) {
+    VarDecl *VD = dyn_cast<VarDecl>(D);
     if (!VD || VD->getStorageClass() == SC_Static)
       continue;
     const Type *Ty = VD->getType()->getUnqualifiedDesugaredType();
     if (FieldDecl *FD = createFieldForHostLayoutStruct(
-            S, Ty, VD->getIdentifier(), LS, BufDecl))
+            S, Ty, VD->getIdentifier(), LS, BufDecl)) {
+      // add the field decl to the layout struct
       LS->addDecl(FD);
+      // update address space of the original decl to hlsl_constant
+      // and disable initialization
+      QualType NewTy =
+          AST.getAddrSpaceQualType(VD->getType(), LangAS::hlsl_constant);
+      VD->setType(NewTy);
+      VD->setInit(nullptr);
----------------
hekota wrote:

If we need to preserve the initializers in the AST even though they are not used, we could mark the generated global variable as `externally_initialized`. The global gets removed in the final DXIL after all.

https://github.com/llvm/llvm-project/pull/123411