[clang] [HLSL] Add codegen for accessing resource members of a struct (PR #187127)

[Joshua Batista via cfe-commits]

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@@ -96,24 +96,119 @@ void addRootSignatureMD(llvm::dxbc::RootSignatureVersion RootSigVer,
   RootSignatureValMD->addOperand(MDVals);
 }
 
+// Gived a MemberExpr of a resource or resource array type, find the parent
+// VarDecl of the struct or class instance that contains this resource and
+// build the full resource name based on the member access path.
+//
+// For example, for a member access like "myStructArray[0].memberA",
+// this function will find the VarDecl of "myStructArray" and use the
+// EmbeddedResourceNameBuilder to build the resource name
+// "myStructArray.0.memberA".
+static const VarDecl *findStructResourceParentDeclAndBuildName(
+    const MemberExpr *ME, EmbeddedResourceNameBuilder &NameBuilder) {
+
+  SmallVector<const Expr *> WorkList;
+  const VarDecl *VD = nullptr;
+  const Expr *E = ME;
+
+  for (;;) {
+    if (const auto *DRE = dyn_cast<DeclRefExpr>(E)) {
+      assert(isa<VarDecl>(DRE->getDecl()) &&
+             "member expr base is not a var decl");
+      VD = cast<VarDecl>(DRE->getDecl());
+      NameBuilder.pushName(VD->getName());
+      break;
+    }
+
+    WorkList.push_back(E);
+    if (const auto *ME = dyn_cast<MemberExpr>(E))
+      E = ME->getBase();
+    else if (const auto *ICE = dyn_cast<ImplicitCastExpr>(E))
+      E = ICE->getSubExpr();
+    else if (const auto *ASE = dyn_cast<ArraySubscriptExpr>(E))
+      E = ASE->getBase();
+    else if (isa<CXXThisExpr>(E))
+      // Resource member access on "this" pointer not yet implemented
+      // (llvm/llvm-project#190299)
+      return nullptr;
+    else
+      llvm_unreachable("unexpected expr type in resource member access");
+  }
+
+  while (!WorkList.empty()) {
+    E = WorkList.pop_back_val();
+    if (const auto *ME = dyn_cast<MemberExpr>(E)) {
+      NameBuilder.pushName(
+          ME->getMemberNameInfo().getName().getAsIdentifierInfo()->getName());
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bob80905 wrote:

Yes they look like they would be handled the same way, which means they both require identifier info, which I'm not sure is reliable for implicit members.
IIRC, my concern was that getAsIdentifierInfo() would be null, or something such that getName would be empty / unexpected, for implicit members. 

https://github.com/llvm/llvm-project/pull/187127