Index: llvm/trunk/include/llvm/Target/TargetMachine.h
===================================================================
--- llvm/trunk/include/llvm/Target/TargetMachine.h
+++ llvm/trunk/include/llvm/Target/TargetMachine.h
@@ -201,6 +201,9 @@
   bool getO0WantsFastISel() { return O0WantsFastISel; }
   void setO0WantsFastISel(bool Enable) { O0WantsFastISel = Enable; }
   void setGlobalISel(bool Enable) { Options.EnableGlobalISel = Enable; }
+  void setGlobalISelAbort(GlobalISelAbortMode Mode) {
+    Options.GlobalISelAbort = Mode;
+  }
   void setMachineOutliner(bool Enable) {
     Options.EnableMachineOutliner = Enable;
   }
Index: llvm/trunk/include/llvm/Target/TargetOptions.h
===================================================================
--- llvm/trunk/include/llvm/Target/TargetOptions.h
+++ llvm/trunk/include/llvm/Target/TargetOptions.h
@@ -96,6 +96,14 @@
     SCE       // Tune debug info for SCE targets (e.g. PS4).
   };
 
+  /// Enable abort calls when global instruction selection fails to lower/select
+  /// an instruction.
+  enum class GlobalISelAbortMode {
+    Disable,        // Disable the abort.
+    Enable,         // Enable the abort.
+    DisableWithDiag // Disable the abort but emit a diagnostic on failure.
+  };
+
   class TargetOptions {
   public:
     TargetOptions()
@@ -192,6 +200,10 @@
     /// EnableGlobalISel - This flag enables global instruction selection.
     unsigned EnableGlobalISel : 1;
 
+    /// EnableGlobalISelAbort - Control abort behaviour when global instruction
+    /// selection fails to lower/select an instruction.
+    GlobalISelAbortMode GlobalISelAbort = GlobalISelAbortMode::Enable;
+
     /// UseInitArray - Use .init_array instead of .ctors for static
     /// constructors.
     unsigned UseInitArray : 1;
Index: llvm/trunk/lib/CodeGen/TargetPassConfig.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/TargetPassConfig.cpp
+++ llvm/trunk/lib/CodeGen/TargetPassConfig.cpp
@@ -137,13 +137,15 @@
     "print-machineinstrs", cl::ValueOptional, cl::desc("Print machine instrs"),
     cl::value_desc("pass-name"), cl::init("option-unspecified"), cl::Hidden);
 
-static cl::opt<int> EnableGlobalISelAbort(
+static cl::opt<GlobalISelAbortMode> EnableGlobalISelAbort(
     "global-isel-abort", cl::Hidden,
     cl::desc("Enable abort calls when \"global\" instruction selection "
-             "fails to lower/select an instruction: 0 disable the abort, "
-             "1 enable the abort, and "
-             "2 disable the abort but emit a diagnostic on failure"),
-    cl::init(1));
+             "fails to lower/select an instruction"),
+    cl::values(
+        clEnumValN(GlobalISelAbortMode::Disable, "0", "Disable the abort"),
+        clEnumValN(GlobalISelAbortMode::Enable, "1", "Enable the abort"),
+        clEnumValN(GlobalISelAbortMode::DisableWithDiag, "2",
+                   "Disable the abort but emit a diagnostic on failure")));
 
 // Temporary option to allow experimenting with MachineScheduler as a post-RA
 // scheduler. Targets can "properly" enable this with
@@ -384,6 +386,9 @@
   if (TM.Options.EnableIPRA)
     setRequiresCodeGenSCCOrder();
 
+  if (EnableGlobalISelAbort.getNumOccurrences())
+    TM.Options.GlobalISelAbort = EnableGlobalISelAbort;
+
   setStartStopPasses();
 }
 
@@ -721,8 +726,11 @@
   // Enable FastISel with -fast-isel, but allow that to be overridden.
   TM->setO0WantsFastISel(EnableFastISelOption != cl::BOU_FALSE);
   if (EnableFastISelOption == cl::BOU_TRUE ||
-      (TM->getOptLevel() == CodeGenOpt::None && TM->getO0WantsFastISel()))
+      (TM->getOptLevel() == CodeGenOpt::None && TM->getO0WantsFastISel() &&
+       !TM->Options.EnableGlobalISel)) {
     TM->setFastISel(true);
+    TM->setGlobalISel(false);
+  }
 
   // Ask the target for an instruction selector.
   // Explicitly enabling fast-isel should override implicitly enabled
@@ -730,6 +738,7 @@
   if (EnableGlobalISelOption == cl::BOU_TRUE ||
       (EnableGlobalISelOption == cl::BOU_UNSET &&
        TM->Options.EnableGlobalISel && EnableFastISelOption != cl::BOU_TRUE)) {
+    TM->setGlobalISel(true);
     TM->setFastISel(false);
 
     SaveAndRestore<bool> SavedAddingMachinePasses(AddingMachinePasses, true);
@@ -1165,14 +1174,9 @@
 /// GlobalISel Configuration
 //===---------------------------------------------------------------------===//
 bool TargetPassConfig::isGlobalISelAbortEnabled() const {
-  if (EnableGlobalISelAbort.getNumOccurrences() > 0)
-    return EnableGlobalISelAbort == 1;
-
-  // When no abort behaviour is specified, we don't abort if the target says
-  // that GISel is enabled.
-  return !TM->Options.EnableGlobalISel;
+  return TM->Options.GlobalISelAbort == GlobalISelAbortMode::Enable;
 }
 
 bool TargetPassConfig::reportDiagnosticWhenGlobalISelFallback() const {
-  return EnableGlobalISelAbort == 2;
+  return TM->Options.GlobalISelAbort == GlobalISelAbortMode::DisableWithDiag;
 }
Index: llvm/trunk/lib/Target/AArch64/AArch64TargetMachine.cpp
===================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ llvm/trunk/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -275,8 +275,10 @@
   }
 
   // Enable GlobalISel at or below EnableGlobalISelAt0.
-  if (getOptLevel() <= EnableGlobalISelAtO)
+  if (getOptLevel() <= EnableGlobalISelAtO) {
     setGlobalISel(true);
+    setGlobalISelAbort(GlobalISelAbortMode::Disable);
+  }
 
   // AArch64 supports the MachineOutliner.
   setMachineOutliner(true);