[CodeGen] Add a -trap-unreachable option for debugging

[dmgreen]

Summary

Add a common -trap-unreachable option, similar to the target
specific hexagon equivalent, which has been replaced. This
turns unreachable instructions into traps, which is useful for
debugging.

[olista01]

Would it be possible to enable this for all targets, not just ARM? Maybe this could be put into the constructor of LLVMTargetMachine?

[dmgreen]

Sounds like a good idea. Now for all targets. I have not removed the hexagon option, in case it was being used by them.

[kparzysz]

You can remove the Hexagon-specific option. It's used in one testcase, you can replace it with the one you introduced.

[dmgreen]

Thanks! Now removes the old option.

[olista01]

LGTM.

lib/Target/ARM/ARMTargetMachine.cpp

EnableARMLoadStoreOpt("arm-load-store-opt", cl::Hidden,
                       cl::desc("Enable ARM load/store optimization pass"),
                       cl::init(true));
 
 // FIXME: Unify control over GlobalMerge.
 static cl::opt<cl::boolOrDefault>
 EnableGlobalMerge("arm-global-merge", cl::Hidden,
                   cl::desc("Enable the global merge pass"));
 
+static cl::opt<bool> EnableTrapUnreachable("arm-trap-unreachable",
+  cl::Hidden, cl::ZeroOrMore, cl::init(false),
+  cl::desc("Enable generating trap for unreachable"));
+
 namespace llvm {
   void initializeARMExecutionDomainFixPass(PassRegistry&);
 }
 
 extern "C" void LLVMInitializeARMTarget() {
   // Register the target.
   RegisterTargetMachine<ARMLETargetMachine> X(getTheARMLETarget());
   RegisterTargetMachine<ARMLETargetMachine> A(getTheThumbLETarget());
if ((TargetTriple.getEnvironment() == Triple::GNUEABI ||
          TargetTriple.getEnvironment() == Triple::MuslEABI ||
          TargetTriple.getEnvironment() == Triple::MuslEABIHF) &&
         !(TargetTriple.isOSWindows() || TargetTriple.isOSDarwin()))
       this->Options.EABIVersion = EABI::GNU;
     else
       this->Options.EABIVersion = EABI::EABI5;
   }
 
+  if (EnableTrapUnreachable)
+    this->Options.TrapUnreachable = true;
+
   initAsmInfo();
 }
 
 ARMBaseTargetMachine::~ARMBaseTargetMachine() = default;
 
 const ARMSubtarget *
 ARMBaseTargetMachine::getSubtargetImpl(const Function &F) const {
   Attribute CPUAttr = F.getFnAttribute("target-cpu");

test/CodeGen/ARM/trap-unreachable.ll

+; RUN: llc -mtriple=thumbv7 -arm-trap-unreachable < %s | FileCheck %s
+; CHECK: .inst.n 0xdefe
+
+define void @test() #0 {
+  unreachable
+}
+
+attributes #0 = { nounwind }