fixup! [ModuloSchedule] Implement modulo variable expansion for pipelining

Author: ytmukai

llvm/lib/CodeGen/ModuloSchedule.cpp

@@ -2670,7 +2670,7 @@ void ModuloScheduleExpanderMVE::expand() {
 /// Check if ModuloScheduleExpanderMVE can be applied to L
 bool ModuloScheduleExpanderMVE::canApply(MachineLoop &L) {
   if (!L.getExitBlock()) {
-    LLVM_DEBUG(dbgs() << "Can not apply MVE expander\n";);
+    LLVM_DEBUG(dbgs() << "Can not apply MVE expander: No single exit block\n";);
     return false;
   }
 
@@ -2687,7 +2687,8 @@ bool ModuloScheduleExpanderMVE::canApply(MachineLoop &L) {
       if (MO.isReg())
         for (MachineInstr &Ref : MRI.use_instructions(MO.getReg()))
           if (Ref.getParent() != BB || Ref.isPHI()) {
-            LLVM_DEBUG(dbgs() << "Can not apply MVE expander\n";);
+            LLVM_DEBUG(dbgs() << "Can not apply MVE expander: A phi result is "
+                                 "referenced outside of the loop or by phi.";);
             return false;
           }
 
@@ -2698,11 +2699,14 @@ bool ModuloScheduleExpanderMVE::canApply(MachineLoop &L) {
     getPhiRegs(MI, MI.getParent(), InitVal, LoopVal);
     if (!Register(LoopVal).isVirtual() ||
         MRI.getVRegDef(LoopVal)->getParent() != BB) {
-      LLVM_DEBUG(dbgs() << "Can not apply MVE expander\n";);
+      LLVM_DEBUG(
+          dbgs() << "Can not apply MVE expander: A phi source value coming "
+                    "from the loop is not defined in the loop.\n";);
       return false;
     }
     if (UsedByPhi.count(LoopVal)) {
-      LLVM_DEBUG(dbgs() << "Can not apply MVE expander\n";);
+      LLVM_DEBUG(dbgs() << "Can not apply MVE expander: A value defined in the "
+                           "loop is referenced by two or more phis.\n";);
       return false;
     }
     UsedByPhi.insert(LoopVal);