Index: lib/Target/ARM/ARMSubtarget.cpp
===================================================================
--- lib/Target/ARM/ARMSubtarget.cpp
+++ lib/Target/ARM/ARMSubtarget.cpp
@@ -144,8 +144,6 @@
                           ? (ARMBaseInstrInfo *)new ARMInstrInfo(*this)
                           : (ARMBaseInstrInfo *)new Thumb2InstrInfo(*this)),
       TLInfo(TM, *this) {
-  assert((isThumb() || hasARMOps()) &&
-         "Target must either be thumb or support ARM operations!");
 
 #ifndef LLVM_BUILD_GLOBAL_ISEL
   GISelAccessor *GISel = new GISelAccessor();
Index: lib/Target/ARM/ARMTargetMachine.cpp
===================================================================
--- lib/Target/ARM/ARMTargetMachine.cpp
+++ lib/Target/ARM/ARMTargetMachine.cpp
@@ -266,7 +266,12 @@
     // function that reside in TargetOptions.
     resetTargetOptions(F);
     I = llvm::make_unique<ARMSubtarget>(TargetTriple, CPU, FS, *this, isLittle);
+
+    if (!I->isThumb() && !I->hasARMOps())
+      F.getContext().emitError("Function '" + F.getName() + "' uses ARM "
+          "instructions, but the target does not support ARM mode execution.");
   }
+
   return I.get();
 }
 
Index: test/CodeGen/ARM/no-arm-mode.ll
===================================================================
--- test/CodeGen/ARM/no-arm-mode.ll
+++ test/CodeGen/ARM/no-arm-mode.ll
@@ -0,0 +1,21 @@
+; RUN: not llc -mtriple=armv7-windows-itanium -mcpu=cortex-a9 -o /dev/null %s 2>&1 \
+; RUN:   | FileCheck %s -check-prefixes=CHECK-OPTIONS,CHECK-FEATURE
+
+; RUN: not llc -mtriple=thumb-unknown-linux -mcpu=cortex-m0 -o /dev/null %s 2>&1 \
+; RUN:   | FileCheck %s -check-prefix=CHECK-FEATURE
+
+define void @foo() {
+entry:
+  ret void
+}
+
+; CHECK-OPTIONS: Function 'foo' uses ARM instructions, but the target does not support ARM mode execution.
+
+define void @no_thumb_mode_feature() #0 {
+entry:
+  ret void
+}
+
+; CHECK-FEATURE: Function 'no_thumb_mode_feature' uses ARM instructions, but the target does not support ARM mode execution.
+
+attributes #0 = { "target-features"="-thumb-mode" }