[TargetPassConfig] Add a target hook to know what GlobalISel should do on error.

By default, this hook tells GlobalISel to abort (report a fatal error)
when it encounters an error. The alternative will be to fall back on
SDISel.
This fall back will be removed when the bring-up of GlobalISel is over.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279879 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/TargetPassConfig.h

@@ -281,6 +281,11 @@ public:
   /// verification is enabled.
   void addVerifyPass(const std::string &Banner);
 
+  /// Check whether or not GlobalISel should abort on error.
+  /// When this is disable, GlobalISel will fall back on SDISel instead of
+  /// erroring out.
+  virtual bool isGlobalISelAbortEnabled() const;
+
 protected:
   // Helper to verify the analysis is really immutable.
   void setOpt(bool &Opt, bool Val);

lib/CodeGen/TargetPassConfig.cpp

@@ -98,6 +98,12 @@ PrintMachineInstrs("print-machineinstrs", cl::ValueOptional,
                    cl::desc("Print machine instrs"),
                    cl::value_desc("pass-name"), cl::init("option-unspecified"));
 
+static cl::opt<bool> EnableGlobalISelAbort(
+    "global-isel-abort", cl::Hidden,
+    cl::desc("Enable abort calls when \"global\" instruction selection "
+             "fails to lower/select an instruction"),
+    cl::init(true));
+
 // Temporary option to allow experimenting with MachineScheduler as a post-RA
 // scheduler. Targets can "properly" enable this with
 // substitutePass(&PostRASchedulerID, &PostMachineSchedulerID).
@@ -888,3 +894,10 @@ void TargetPassConfig::addBlockPlacement() {
       addPass(&MachineBlockPlacementStatsID);
   }
 }
+
+//===---------------------------------------------------------------------===//
+/// GlobalISel Configuration
+//===---------------------------------------------------------------------===//
+bool TargetPassConfig::isGlobalISelAbortEnabled() const {
+  return EnableGlobalISelAbort;
+}