diff --git a/TODO.md b/TODO.md
index 76aee0383..c3e77707d 100644
--- a/TODO.md
+++ b/TODO.md
@@ -20,6 +20,7 @@ andix
 orx
 
 rlwinmx
+rlwimix
 rldiclx
 extsbx
 slwx
diff --git a/src/cpu/codegen/function_generator.cc b/src/cpu/codegen/function_generator.cc
index 98fd4d8ad..433db45dd 100644
--- a/src/cpu/codegen/function_generator.cc
+++ b/src/cpu/codegen/function_generator.cc
@@ -199,6 +199,8 @@ void FunctionGenerator::GenerateBasicBlock(FunctionBlock* block,
   builder_->SetInsertPoint(bb);
   //i->setMetadata("some.name", MDNode::get(context, MDString::get(context, pname)));
 
+  Value* invalidInstruction =
+      gen_module_->getGlobalVariable("XeInvalidInstruction");
   Value* traceInstruction =
       gen_module_->getGlobalVariable("XeTraceInstruction");
 
@@ -220,7 +222,13 @@ void FunctionGenerator::GenerateBasicBlock(FunctionBlock* block,
     }
 
     if (!i.type) {
-      XELOGCPU("Invalid instruction at %.8X: %.8X\n", ia, i.code);
+      XELOGCPU("Invalid instruction %.8X %.8X", ia, i.code);
+      SpillRegisters();
+      builder_->CreateCall3(
+          invalidInstruction,
+          gen_fn_->arg_begin(),
+          builder_->getInt32(i.address),
+          builder_->getInt32(i.code));
       continue;
     }
     printf("    %.8X: %.8X %s\n", ia, i.code, i.type->name);
@@ -235,7 +243,17 @@ void FunctionGenerator::GenerateBasicBlock(FunctionBlock* block,
     XEASSERTNOTNULL(emit);
     int result = emit(*this, *builder_, i);
     if (result) {
-      printf("---- error generating instruction: %.8X\n", ia);
+      // This printf is handy for sort/uniquify to find instructions.
+      //printf("unimplinstr %s\n", i.type->name);
+
+      XELOGCPU("Unimplemented instr %.8X %.8X %s",
+               ia, i.code, i.type->name);
+      SpillRegisters();
+      builder_->CreateCall3(
+          invalidInstruction,
+          gen_fn_->arg_begin(),
+          builder_->getInt32(i.address),
+          builder_->getInt32(i.code));
     }
   }
 
diff --git a/src/cpu/exec_module.cc b/src/cpu/exec_module.cc
index 01170e22e..7de1fda40 100644
--- a/src/cpu/exec_module.cc
+++ b/src/cpu/exec_module.cc
@@ -207,6 +207,11 @@ void XeIndirectBranch(xe_ppc_state_t* state, uint64_t target, uint64_t br_ia) {
   XEASSERTALWAYS();
 }
 
+void XeInvalidInstruction(xe_ppc_state_t* state, uint32_t cia, uint32_t data) {
+  // TODO(benvanik): handle better
+  XELOGCPU("INVALID INSTRUCTION %.8X %.8X", cia, data);
+}
+
 void XeTraceKernelCall(xe_ppc_state_t* state, uint64_t cia, uint64_t call_ia) {
   // TODO(benvanik): get names
   XELOGCPU("TRACE: %.8X -> k.%.8X", (uint32_t)call_ia, (uint32_t)cia);
@@ -261,6 +266,18 @@ int ExecModule::InjectGlobals() {
                           "XeIndirectBranch");
   engine_->addGlobalMapping(gv, (void*)&XeIndirectBranch);
 
+  // Debugging methods:
+  std::vector<Type*> invalidInstructionArgs;
+  invalidInstructionArgs.push_back(int8PtrTy);
+  invalidInstructionArgs.push_back(Type::getInt32Ty(context));
+  invalidInstructionArgs.push_back(Type::getInt32Ty(context));
+  FunctionType* invalidInstructionTy = FunctionType::get(
+      Type::getVoidTy(context), invalidInstructionArgs, false);
+  gv = new GlobalVariable(*gen_module_, invalidInstructionTy, true,
+                          GlobalVariable::ExternalLinkage, 0,
+                          "XeInvalidInstruction");
+  engine_->addGlobalMapping(gv, (void*)&XeInvalidInstruction);
+
   // Tracing methods:
   std::vector<Type*> traceCallArgs;
   traceCallArgs.push_back(int8PtrTy);