Debug Info: Simplify Frame Index handling in DBG_VALUE Machine Instructions

Rather than using the full power of target-specific addressing modes in
DBG_VALUEs with Frame Indicies, simply use Frame Index + Offset. This
reduces the complexity of debug info handling down to two
representations of values (reg+offset and frame index+offset) rather
than three or four.

Ideally we could ensure that frame indicies had been eliminated by the
time we reached an assembly or dwarf generation, but I haven't spent the
time to figure out where the FIs are leaking through into that & whether
there's a good place to convert them. Some FI+offset=>reg+offset
conversion is done (see PrologEpilogInserter, for example) which is
necessary for some SelectionDAG assumptions about registers, I believe,
but it might be possible to make this a more thorough conversion &
ensure there are no remaining FIs no matter how instruction selection
is performed.

llvm-svn: 184066

llvm/lib/CodeGen/LiveDebugVariables.cpp

@@ -921,17 +921,6 @@ void UserValue::insertDebugValue(MachineBasicBlock *MBB, SlotIndex Idx,
   MachineOperand &Loc = locations[LocNo];
   ++NumInsertedDebugValues;
 
-  // Frame index locations may require a target callback.
-  if (Loc.isFI()) {
-    MachineInstr *MI = TII.emitFrameIndexDebugValue(*MBB->getParent(),
-                                          Loc.getIndex(), offset, variable, 
-                                                    findDebugLoc());
-    if (MI) {
-      MBB->insert(I, MI);
-      return;
-    }
-  }
-  // This is not a frame index, or the target is happy with a standard FI.
   BuildMI(*MBB, I, findDebugLoc(), TII.get(TargetOpcode::DBG_VALUE))
     .addOperand(Loc).addImm(offset).addMetadata(variable);
 }
@@ -992,4 +981,3 @@ void LiveDebugVariables::dump() {
     static_cast<LDVImpl*>(pImpl)->print(dbgs());
 }
 #endif
-