[debugify] Add way to omit debug-location from MIR output

[dsanders]

Summary

In lieu of a proper pass that strips debug info, add a way
to omit debug-locations from the MIR output so that
instructions with MMO's continue to match CHECK's when
mir-debugify is used

[dsanders]

I haven't added a test case for this as D77576 covers it

[vsk]

Why not generalize this to something like -mir-print-debug-info, which, when set to false, makes the MIR printer stop printing DBG_ meta instructions as well? Then you might not need D77438.

[dsanders]

In D77575#1964990, @vsk wrote:

Why not generalize this to something like -mir-print-debug-info, which, when set to false, makes the MIR printer stop printing DBG_ meta instructions as well? Then you might not need D77438.

My preference is to have a debug info stripping pass which you can include in your pipeline so that there's none left for the printer to print but I haven't done that yet. The change in D77438 is still needed for other reasons though. It's a bug but DEBUG_VALUE affects CodeGen quite a bit as it causes hasOneUse() to return false when it would otherwise return true. Most of the backends are using hasOneUse when they probably meant hasOneNonDbgUse() but it's also not a simple replacement as you still need to do something about the DEBUG_VALUE. D77438 allows backends to make progress on location preservation without dealing with their DEBUG_VALUE bugs at the same time.

[vsk]

Ok, I think this is fine then.

[aprantl]

In lieu of a proper pass that strips debug info

What is it that you need? Something like llvm::stripDebugInfo() (from DebugInfo.cpp) but for MIR? That should be very easy to adapt.

[dsanders]

In D77575#1965264, @aprantl wrote:

In lieu of a proper pass that strips debug info

What is it that you need? Something like llvm::stripDebugInfo() (from DebugInfo.cpp) but for MIR? That should be very easy to adapt.

Yes, it's essentially stripDebugInfo() for MIR along with a pass wrapper that just calls it. The reason for wrapping it in a pass is that you can then go on to something akin to -verify-machineinstrs but with a pipeline like mir-debugify,<pass1>,strip-mir-debug,mir-debugify,<pass2>,strip-mir-debug. At that point Pass2's ability to test for location loss isn't dependent on Pass1's ability to preserve the locations from the first mir-debugify.

llvm/lib/CodeGen/MIRPrinter.cpp

 #include <vector>
 
 using namespace llvm;
 
 static cl::opt<bool> SimplifyMIR(
     "simplify-mir", cl::Hidden,
     cl::desc("Leave out unnecessary information when printing MIR"));
 
+static cl::opt<bool> PrintLocations("mir-debug-loc", cl::Hidden, cl::init(true),
+                                    cl::desc("Print MIR debug-locations"));
+
 namespace {
 
 /// This structure describes how to print out stack object references.
 struct FrameIndexOperand {
   std::string Name;
   unsigned ID;
   bool IsFixed;
 
void MIPrinter::print(const MachineInstr &MI) {
   if (MDNode *HeapAllocMarker = MI.getHeapAllocMarker()) {
     if (NeedComma)
       OS << ',';
     OS << " heap-alloc-marker ";
     HeapAllocMarker->printAsOperand(OS, MST);
     NeedComma = true;
   }
 
+  if (PrintLocations) {
     if (const DebugLoc &DL = MI.getDebugLoc()) {
       if (NeedComma)
         OS << ',';
       OS << " debug-location ";
       DL->printAsOperand(OS, MST);
     }
+  }
 
   if (!MI.memoperands_empty()) {
     OS << " :: ";
     const LLVMContext &Context = MF->getFunction().getContext();
     const MachineFrameInfo &MFI = MF->getFrameInfo();
     bool NeedComma = false;
     for (const auto *Op : MI.memoperands()) {
       if (NeedComma)