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

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

Reviewers: qcolombet, bogner, aprantl, vsk, paquette

Subscribers: rovka, hiraditya, volkan, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78261

Author: dsandersllvm

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

@@ -115,6 +115,12 @@ void reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
                         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,

llvm/lib/CodeGen/GlobalISel/Utils.cpp

@@ -198,22 +198,37 @@ bool llvm::isTriviallyDead(const MachineInstr &MI,
   return true;
 }
 
-void llvm::reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
-                              MachineOptimizationRemarkEmitter &MORE,
-                              MachineOptimizationRemarkMissed &R) {
-  MF.getProperties().set(MachineFunctionProperties::Property::FailedISel);
-
+static void reportGISelDiagnostic(DiagnosticSeverity Severity,
+                                  MachineFunction &MF,
+                                  const TargetPassConfig &TPC,
+                                  MachineOptimizationRemarkEmitter &MORE,
+                                  MachineOptimizationRemarkMissed &R) {
+  bool IsFatal = Severity == DS_Error &&
+                 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(DS_Warning, MF, TPC, MORE, R);
+}
+
+void llvm::reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
+                              MachineOptimizationRemarkEmitter &MORE,
+                              MachineOptimizationRemarkMissed &R) {
+  MF.getProperties().set(MachineFunctionProperties::Property::FailedISel);
+  reportGISelDiagnostic(DS_Error, MF, TPC, MORE, R);
+}
+
 void llvm::reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
                               MachineOptimizationRemarkEmitter &MORE,
                               const char *PassName, StringRef Msg,