From f5b6c2b9cfcf40b5591d73707f530759a9159fa8 Mon Sep 17 00:00:00 2001
From: "William S. Moses" <gh@wsmoses.com>
Date: Fri, 24 Dec 2021 13:08:40 -0500
Subject: [PATCH] Handle switch without cases

---
 tools/mlir-clang/Lib/CGStmt.cc                  |  7 +++++++
 tools/mlir-clang/Test/Verification/switchnone.c | 12 ++++++++++++
 2 files changed, 19 insertions(+)
 create mode 100644 tools/mlir-clang/Test/Verification/switchnone.c

diff --git a/tools/mlir-clang/Lib/CGStmt.cc b/tools/mlir-clang/Lib/CGStmt.cc
index 6937ac8..3c86a04 100644
--- a/tools/mlir-clang/Lib/CGStmt.cc
+++ b/tools/mlir-clang/Lib/CGStmt.cc
@@ -650,6 +650,13 @@ ValueCategory MLIRScanner::VisitSwitchStmt(clang::SwitchStmt *stmt) {
     }
   }
 
+  if (caseVals.size() == 0) {
+      delete &exitB;
+      er.erase();
+      builder.setInsertionPoint(oldblock2, oldpoint2);
+      return nullptr;
+  }
+
   if (inCase)
     loops.pop_back();
   builder.create<mlir::BranchOp>(loc, &exitB);
diff --git a/tools/mlir-clang/Test/Verification/switchnone.c b/tools/mlir-clang/Test/Verification/switchnone.c
new file mode 100644
index 0000000..0446b60
--- /dev/null
+++ b/tools/mlir-clang/Test/Verification/switchnone.c
@@ -0,0 +1,12 @@
+// RUN: mlir-clang %s --function=foo -S | FileCheck %s
+
+int foo(int t) {
+  switch (t) {
+  }
+  return t;
+}
+
+// TODO the select should be canonicalized better
+// CHECK:   func @foo(%arg0: i32) -> i32 attributes {llvm.linkage = #llvm.linkage<external>} {
+// CHECK-NEXT:     return %arg0 : i32
+// CHECK-NEXT:   }