From: Dale Johannesen <dalej@apple.com>
Date: Wed, 27 Jan 2010 22:12:36 +0000 (+0000)
Subject: If the only use of something is a DEBUG_VALUE, don't
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=9514fcbae518cfe3e4e4ea1fcc279babbdc38095;p=oota-llvm.git

If the only use of something is a DEBUG_VALUE, don't
let that stop it from being deleted, and change the
DEBUG_VALUE value to undef.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94694 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/DeadMachineInstructionElim.cpp b/lib/CodeGen/DeadMachineInstructionElim.cpp
index 0982eabff12..9d7ec06ac97 100644
--- a/lib/CodeGen/DeadMachineInstructionElim.cpp
+++ b/lib/CodeGen/DeadMachineInstructionElim.cpp
@@ -107,6 +107,20 @@ bool DeadMachineInstructionElim::runOnMachineFunction(MachineFunction &MF) {
          MIE = MBB->rend(); MII != MIE; ) {
       MachineInstr *MI = &*MII;
 
+      if (MI->getOpcode()==TargetInstrInfo::DEBUG_VALUE) {
+        // Don't delete the DEBUG_VALUE itself, but if its Value operand is
+        // a vreg and this is the only use, substitute an undef operand;
+        // the former operand will then be deleted normally.
+        if (MI->getNumOperands()==3 && MI->getOperand(0).isReg()) {
+          unsigned Reg = MI->getOperand(0).getReg();
+          MachineRegisterInfo::use_iterator I = MRI->use_begin(Reg);
+          assert(I != MRI->use_end());
+          if (++I == MRI->use_end())
+            // only one use, which must be this DEBUG_VALUE.
+            MI->getOperand(0).setReg(0U);
+        }
+      }
+
       // If the instruction is dead, delete it!
       if (isDead(MI)) {
         DEBUG(dbgs() << "DeadMachineInstructionElim: DELETING: " << *MI);