[globalisel] Allow backends to report an issue without triggering fallback. NFC

[dsanders]

Summary

This will allow us to fix the issue where the lost locations
verifier causes CodeGen changes on lost locations because it
falls back on DAGISel

[qcolombet]

LGTM with the bool to enum change.

llvm/lib/CodeGen/GlobalISel/Utils.cpp

201

Instead of AllowFatal could we have a severity enum?
For now, maybe just warning and failure, where failure would be equivalent to AllowFatal == true?

[dsanders]

Thanks

llvm/lib/CodeGen/GlobalISel/Utils.cpp

201

Sure, I'll re-use DiagnosticSeverity

llvm/include/llvm/CodeGen/GlobalISel/Utils.h

void reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
                         MachineOptimizationRemarkEmitter &MORE,
                         MachineOptimizationRemarkMissed &R);
 
 void reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
                         MachineOptimizationRemarkEmitter &MORE,
                         const char *PassName, StringRef Msg,
                         const MachineInstr &MI);
 
+/// Report an ISel warning as a missed optimization remark to the LLVMContext's
+/// diagnostic stream.
+void reportGISelWarning(MachineFunction &MF, const TargetPassConfig &TPC,
+                        MachineOptimizationRemarkEmitter &MORE,
+                        MachineOptimizationRemarkMissed &R);
+
 /// If \p VReg is defined by a G_CONSTANT fits in int64_t
 /// returns it.
 Optional<int64_t> getConstantVRegVal(Register VReg,
                                      const MachineRegisterInfo &MRI);
 /// Simple struct used to hold a constant integer value and a virtual
 /// register.
 struct ValueAndVReg {
   int64_t Value;

llvm/lib/CodeGen/GlobalISel/Utils.cpp

for (auto &MO : MI.operands()) {
 
     Register Reg = MO.getReg();
     if (Register::isPhysicalRegister(Reg) || !MRI.use_nodbg_empty(Reg))
       return false;
   }
   return true;
 }
 
-void llvm::reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
+static void reportGISelDiagnostic(bool AllowFatal, MachineFunction &MF,
+                                  const TargetPassConfig &TPC,
                                   MachineOptimizationRemarkEmitter &MORE,
                                   MachineOptimizationRemarkMissed &R) {
-  MF.getProperties().set(MachineFunctionProperties::Property::FailedISel);
-
+  bool IsFatal = AllowFatal && TPC.isGlobalISelAbortEnabled();
   // Print the function name explicitly if we don't have a debug location (which
   // makes the diagnostic less useful) or if we're going to emit a raw error.
-  if (!R.getLocation().isValid() || TPC.isGlobalISelAbortEnabled())
+  if (!R.getLocation().isValid() || IsFatal)
     R << (" (in function: " + MF.getName() + ")").str();
 
-  if (TPC.isGlobalISelAbortEnabled())
+  if (IsFatal)
     report_fatal_error(R.getMsg());
   else
     MORE.emit(R);
 }
 
+void llvm::reportGISelWarning(MachineFunction &MF, const TargetPassConfig &TPC,
+                              MachineOptimizationRemarkEmitter &MORE,
+                              MachineOptimizationRemarkMissed &R) {
+  reportGISelDiagnostic(/*AllowFatal=*/false, MF, TPC, MORE, R);
+}
+
+void llvm::reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
+                              MachineOptimizationRemarkEmitter &MORE,
+                              MachineOptimizationRemarkMissed &R) {
+  MF.getProperties().set(MachineFunctionProperties::Property::FailedISel);
+  reportGISelDiagnostic(/*AllowFatal=*/true, MF, TPC, MORE, R);
+}
+
 void llvm::reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
                               MachineOptimizationRemarkEmitter &MORE,
                               const char *PassName, StringRef Msg,
                               const MachineInstr &MI) {
   MachineOptimizationRemarkMissed R(PassName, "GISelFailure: ",
                                     MI.getDebugLoc(), MI.getParent());
   R << Msg;
   // Printing MI is expensive;  only do it if expensive remarks are enabled.