[CIR][CIRGen] Improve switch support for unrecheable code

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -1109,6 +1109,8 @@ class CIRGenFunction : public CIRGenTypeCache {
   buildSwitchCase(const clang::SwitchCase &S, mlir::Type condType,
                   SmallVector<mlir::Attribute, 4> &caseAttrs);
 
+  mlir::LogicalResult buildCaseNoneStmt(const Stmt *stmt);
+
   mlir::LogicalResult
   buildSwitchBody(const clang::Stmt *S, mlir::Type condType,
                   SmallVector<mlir::Attribute, 4> &caseAttrs);
@@ -1898,6 +1900,8 @@ class CIRGenFunction : public CIRGenTypeCache {
 
     void setRetVal(mlir::Value v) { retVal = v; }
 
+    LexicalScope *getParentScope() { return ParentScope; }
+
     void cleanup();
     void restore() { CGF.currLexScope = ParentScope; }
 
@@ -2027,6 +2031,8 @@ class CIRGenFunction : public CIRGenTypeCache {
     // Scope entry block tracking
     mlir::Block *getEntryBlock() { return EntryBlock; }
 
+    bool IsInsideCaseNoneStmt = false;
+
     mlir::Location BeginLoc, EndLoc;
   };
 

clang/lib/CIR/CodeGen/CIRGenStmt.cpp

@@ -24,26 +24,6 @@ using namespace cir;
 using namespace clang;
 using namespace mlir::cir;
 
-namespace {
-
-// Handle stmt that don't belong to any cases.
-void checkCaseNoneStmt(const Stmt &S, bool checkCaseStmt = true) {
-  if (S.getStmtClass() == Stmt::LabelStmtClass)
-    llvm_unreachable("LabelStmtClass support NYI");
-
-  if (S.getStmtClass() == Stmt::CaseStmtClass ||
-      S.getStmtClass() == Stmt::DefaultStmtClass)
-    assert(!checkCaseStmt && "CaseStmtClass/DefaultStmtClass support NYI");
-
-  if (S.getStmtClass() == Stmt::SwitchStmtClass)
-    checkCaseStmt = false;
-
-  for (const Stmt *c : S.children())
-    checkCaseNoneStmt(*c, checkCaseStmt);
-}
-
-} // namespace
-
 Address CIRGenFunction::buildCompoundStmtWithoutScope(const CompoundStmt &S,
                                                       bool getLast,
                                                       AggValueSlot slot) {
@@ -348,6 +328,14 @@ mlir::LogicalResult CIRGenFunction::buildLabelStmt(const clang::LabelStmt &S) {
   // IsEHa: not implemented.
   assert(!(getContext().getLangOpts().EHAsynch && S.isSideEntry()));
 
+  // TODO: After support case stmt crossing scopes, we should build LabelStmt
+  //       and clean LexicalScope::IsInsideCaseNoneStmt.
+  for (auto *lexScope = currLexScope; lexScope;
+       lexScope = lexScope->getParentScope()) {
+    assert(!lexScope->IsInsideCaseNoneStmt &&
+           "LabelStmt inside case none stmt NYI");
+  }
+
   return buildStmt(S.getSubStmt(), /* useCurrentScope */ true);
 }
 
@@ -479,6 +467,11 @@ mlir::LogicalResult CIRGenFunction::buildReturnStmt(const ReturnStmt &S) {
   assert(!UnimplementedFeature::requiresReturnValueCheck());
   auto loc = getLoc(S.getSourceRange());
 
+  // TODO: Rewrite the logic to handle ReturnStmt inside SwitchStmt, then
+  //       clean up the code below.
+  if (currLexScope->IsInsideCaseNoneStmt)
+    return mlir::success();
+
   // Emit the result value, even if unused, to evaluate the side effects.
   const Expr *RV = S.getRetValue();
 
@@ -724,6 +717,22 @@ CIRGenFunction::buildSwitchCase(const SwitchCase &S, mlir::Type condType,
   llvm_unreachable("expect case or default stmt");
 }
 
+mlir::LogicalResult CIRGenFunction::buildCaseNoneStmt(const Stmt *S) {
+  // Create orphan region to skip over the case none stmts.
+  mlir::Region region;
+  auto *block = builder.createBlock(&region);
+  mlir::OpBuilder::InsertionGuard guard(builder);
+  builder.setInsertionPointToStart(block);
+
+  currLexScope->IsInsideCaseNoneStmt = true;
+
+  auto res = buildStmt(S, /*useCurrentScope=*/isa<CompoundStmt>(S));
+
+  currLexScope->IsInsideCaseNoneStmt = false;
+
+  return res;
+}
+
 mlir::LogicalResult
 CIRGenFunction::buildCXXForRangeStmt(const CXXForRangeStmt &S,
                                      ArrayRef<const Attr *> ForAttrs) {
@@ -1004,7 +1013,7 @@ mlir::LogicalResult CIRGenFunction::buildSwitchBody(
         builder.setInsertionPointToEnd(lastCaseBlock);
         res = buildStmt(c, /*useCurrentScope=*/!isa<CompoundStmt>(c));
       } else {
-        checkCaseNoneStmt(*c);
+        buildCaseNoneStmt(c);
         continue;
       }
 
@@ -1016,7 +1025,7 @@ mlir::LogicalResult CIRGenFunction::buildSwitchBody(
     return res;
   }
 
-  checkCaseNoneStmt(*S);
+  buildCaseNoneStmt(S);
   return mlir::success();
 }