[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, 0 insertions, 20 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index aaa8043..284edda 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -682,26 +682,6 @@ void MachineInstr::eraseFromParent() {
   getParent()->erase(this);
 }
 
-void MachineInstr::eraseFromParentAndMarkDBGValuesForRemoval() {
-  assert(getParent() && "Not embedded in a basic block!");
-  MachineBasicBlock *MBB = getParent();
-  MachineFunction *MF = MBB->getParent();
-  assert(MF && "Not embedded in a function!");
-
-  MachineInstr *MI = (MachineInstr *)this;
-  MachineRegisterInfo &MRI = MF->getRegInfo();
-
-  for (const MachineOperand &MO : MI->operands()) {
-    if (!MO.isReg() || !MO.isDef())
-      continue;
-    Register Reg = MO.getReg();
-    if (!Reg.isVirtual())
-      continue;
-    MRI.markUsesInDebugValueAsUndef(Reg);
-  }
-  MI->eraseFromParent();
-}
-
 void MachineInstr::eraseFromBundle() {
   assert(getParent() && "Not embedded in a basic block!");
   getParent()->erase_instr(this);