[CIR][CIRGen] Support for __attribute__((fallthrough)) statement (#517)

This PR adds handling of AttributedStmt to support fallthrough
attribute.

Author: YazZz1k

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -986,6 +986,8 @@ class CIRGenFunction : public CIRGenTypeCache {
   mlir::LogicalResult buildLabel(const clang::LabelDecl *D);
   mlir::LogicalResult buildLabelStmt(const clang::LabelStmt &S);
 
+  mlir::LogicalResult buildAttributedStmt(const AttributedStmt &S);
+
   mlir::LogicalResult buildBreakStmt(const clang::BreakStmt &S);
   mlir::LogicalResult buildContinueStmt(const clang::ContinueStmt &S);
 

clang/lib/CIR/CodeGen/CIRGenStmt.cpp

@@ -306,6 +306,8 @@ mlir::LogicalResult CIRGenFunction::buildSimpleStmt(const Stmt *S,
     return buildBreakStmt(cast<BreakStmt>(*S));
 
   case Stmt::AttributedStmtClass:
+    return buildAttributedStmt(cast<AttributedStmt>(*S));
+
   case Stmt::SEHLeaveStmtClass:
     llvm::errs() << "CIR codegen for '" << S->getStmtClassName()
                  << "' not implemented\n";
@@ -325,6 +327,23 @@ mlir::LogicalResult CIRGenFunction::buildLabelStmt(const clang::LabelStmt &S) {
   return buildStmt(S.getSubStmt(), /* useCurrentScope */ true);
 }
 
+mlir::LogicalResult
+CIRGenFunction::buildAttributedStmt(const AttributedStmt &S) {
+  for (const auto *A : S.getAttrs()) {
+    switch (A->getKind()) {
+    case attr::NoMerge:
+    case attr::NoInline:
+    case attr::AlwaysInline:
+    case attr::MustTail:
+      llvm_unreachable("NIY attributes");
+    default:
+      break;
+    }
+  }
+
+  return buildStmt(S.getSubStmt(), true, S.getAttrs());
+}
+
 // Add terminating yield on body regions (loops, ...) in case there are
 // not other terminators used.
 // FIXME: make terminateCaseRegion use this too.

clang/test/CIR/CodeGen/switch.cpp

@@ -274,3 +274,29 @@ void sw12(int a) {
 // CHECK-NEXT:     ^bb1:  // no predecessors
 // CHECK-NEXT:       cir.break
 // CHECK-NEXT:     }
+
+void fallthrough(int x) {
+  switch (x) {
+    case 1:
+      __attribute__((fallthrough));
+    case 2:
+      break;
+    default:
+      break;
+  }
+}
+
+//      CHECK:  cir.func @_Z11fallthroughi
+//      CHECK:    cir.scope {
+//      CHECK:      cir.switch (%1 : !s32i) [
+// CHECK-NEXT:      case (equal, 1) {
+// CHECK-NEXT:        cir.yield
+// CHECK-NEXT:      },
+// CHECK-NEXT:      case (equal, 2) {
+// CHECK-NEXT:        cir.break
+// CHECK-NEXT:      },
+// CHECK-NEXT:      case (default) {
+// CHECK-NEXT:        cir.break
+// CHECK-NEXT:      }
+// CHECK-NEXT:      ]
+// CHECK-NEXT:    }