Emit error when taking the address of unrecheable blocks

Author: bcardosolopes

mlir/lib/Target/LLVMIR/ModuleImport.cpp

@@ -2440,7 +2440,7 @@ LogicalResult ModuleImport::processFunction(llvm::Function *func) {
     // Skip unreachable blocks.
     if (!reachable.contains(&basicBlock)) {
       if (basicBlock.hasAddressTaken())
-        emitWarning(funcOp.getLoc())
+        emitError(funcOp.getLoc())
             << "unreachable block '" << basicBlock.getName()
             << "' with address taken";
       continue;

mlir/test/Target/LLVMIR/Import/import-failure.ll

@@ -350,3 +350,13 @@ bb2:
 declare i32 @g()
 
 declare i32 @__gxx_personality_v0(...)
+
+; // -----
+
+@g = private global ptr blockaddress(@fn, %bb1)
+define void @fn() {
+  ret void
+; CHECK: unreachable block 'bb1' with address taken
+bb1:
+  ret void
+}