machine combiner: fix pretty printer

we used to print UNKNOWN instructions when the instruction to be printer was not
yet inserted in any BB: in that case the pretty printer would not be able to
compute a TII as the instruction does not belong to any BB or function yet.
This patch explicitly passes the TII to the pretty-printer.

Differential Revision: https://reviews.llvm.org/D27645

llvm-svn: 290228
diff --git a/llvm/lib/CodeGen/MachineCombiner.cpp b/llvm/lib/CodeGen/MachineCombiner.cpp
index 54c4741..5beed5f 100644
--- a/llvm/lib/CodeGen/MachineCombiner.cpp
+++ b/llvm/lib/CodeGen/MachineCombiner.cpp
@@ -135,7 +135,7 @@
   // are tracked in the InstrIdxForVirtReg map depth is looked up in InstrDepth
   for (auto *InstrPtr : InsInstrs) { // for each Use
     unsigned IDepth = 0;
-    DEBUG(dbgs() << "NEW INSTR "; InstrPtr->dump(); dbgs() << "\n";);
+    DEBUG(dbgs() << "NEW INSTR "; InstrPtr->dump(TII); dbgs() << "\n";);
     for (const MachineOperand &MO : InstrPtr->operands()) {
       // Check for virtual register operand.
       if (!(MO.isReg() && TargetRegisterInfo::isVirtualRegister(MO.getReg())))