[GlobalISel] Allow DBG_VALUE to use undefined vregs before LiveDebugValues.

Expanding on D109750.

Since `DBG_VALUE` instructions have final register validity determined in
`LDVImpl::handleDebugValue`, there is no apparent reason to immediately prune
unused register operands as their defs are erased. Consequently, this renders
`MachineInstr::eraseFromParentAndMarkDBGValuesForRemoval` moot; gaining a
substantial performance improvement.

The only necessary changes involve making relevant passes consider invalid
DBG_VALUE vregs uses as valid.

Reviewed By: MatzeB

Differential Revision: https://reviews.llvm.org/D112852

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineFunction.cpp b/llvm/lib/CodeGen/MachineFunction.cpp
index ff3a39ecf0a6..b6f1a6e64e75 100644
--- a/llvm/lib/CodeGen/MachineFunction.cpp
+++ b/llvm/lib/CodeGen/MachineFunction.cpp
@@ -89,6 +89,7 @@ static cl::opt<unsigned> AlignAllFunctions(
 static const char *getPropertyName(MachineFunctionProperties::Property Prop) {
   using P = MachineFunctionProperties::Property;
 
+  // clang-format off
   switch(Prop) {
   case P::FailedISel: return "FailedISel";
   case P::IsSSA: return "IsSSA";
@@ -100,7 +101,9 @@ static const char *getPropertyName(MachineFunctionProperties::Property Prop) {
   case P::TracksLiveness: return "TracksLiveness";
   case P::TiedOpsRewritten: return "TiedOpsRewritten";
   case P::FailsVerification: return "FailsVerification";
+  case P::TracksDebugUserValues: return "TracksDebugUserValues";
   }
+  // clang-format on
   llvm_unreachable("Invalid machine function property");
 }