Revert r178845 - Fix bug in PEI's virtual-register scavenging

Reverting because this breaks one of the LTO builders. Original commit message:

    This change fixes a bug that I introduced in r178058. After a register is
    scavenged using one of the available spills slots the instruction defining the
    virtual register needs to be moved to after the spill code. The scavenger has
    already processed the defining instruction so that registers killed by that
    instruction are available for definition in that same instruction. Unfortunately,
    after this, the scavenger needs to iterate through the spill code and then
    visit, again, the instruction that defines the now-scavenged register. In order
    to avoid confusion, the register scavenger needs the ability to 'back up'
    through the spill code so that it can again process the instructions in the
    appropriate order. Prior to this fix, once the scavenger reached the
    just-moved instruction, it would assert if it killed any registers because,
    having already processed the instruction, it believed they were undefined.

    Unfortunately, I don't yet have a small test case. Thanks to Pranav Bhandarkar
    for diagnosing the problem and testing this fix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178916 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 51 deletions

diff --git a/lib/CodeGen/RegisterScavenging.cpp b/lib/CodeGen/RegisterScavenging.cpp
index 07ace7a..55a66ba 100644
--- a/lib/CodeGen/RegisterScavenging.cpp
+++ b/lib/CodeGen/RegisterScavenging.cpp
@@ -110,11 +110,30 @@ void RegScavenger::addRegWithSubRegs(BitVector &BV, unsigned Reg) {
     BV.set(*SubRegs);
 }
 
-void RegScavenger::determineKillsAndDefs() {
-  assert(Tracking && "Must be tracking to determine kills and defs");
+void RegScavenger::forward() {
+  // Move ptr forward.
+  if (!Tracking) {
+    MBBI = MBB->begin();
+    Tracking = true;
+  } else {
+    assert(MBBI != MBB->end() && "Already past the end of the basic block!");
+    MBBI = llvm::next(MBBI);
+  }
+  assert(MBBI != MBB->end() && "Already at the end of the basic block!");
 
   MachineInstr *MI = MBBI;
-  assert(!MI->isDebugValue() && "Debug values have no kills or defs");
+
+  for (SmallVector<ScavengedInfo, 2>::iterator I = Scavenged.begin(),
+       IE = Scavenged.end(); I != IE; ++I) {
+    if (I->Restore != MI)
+      continue;
+
+    I->Reg = 0;
+    I->Restore = NULL;
+  }
+
+  if (MI->isDebugValue())
+    return;
 
   // Find out which registers are early clobbered, killed, defined, and marked
   // def-dead in this instruction.
@@ -148,54 +167,6 @@ void RegScavenger::determineKillsAndDefs() {
         addRegWithSubRegs(DefRegs, Reg);
     }
   }
-}
-
-void RegScavenger::unprocess() {
-  assert(Tracking && "Cannot unprocess because we're not tracking");
-
-  MachineInstr *MI = MBBI;
-  if (MI->isDebugValue())
-    return;
-
-  determineKillsAndDefs();
-
-  // Commit the changes.
-  setUsed(KillRegs);
-  setUnused(DefRegs);
-
-  if (MBBI == MBB->begin()) {
-    MBBI = MachineBasicBlock::iterator(NULL);
-    Tracking = false;
-  } else
-    --MBBI;
-}
-
-void RegScavenger::forward() {
-  // Move ptr forward.
-  if (!Tracking) {
-    MBBI = MBB->begin();
-    Tracking = true;
-  } else {
-    assert(MBBI != MBB->end() && "Already past the end of the basic block!");
-    MBBI = llvm::next(MBBI);
-  }
-  assert(MBBI != MBB->end() && "Already at the end of the basic block!");
-
-  MachineInstr *MI = MBBI;
-
-  for (SmallVector<ScavengedInfo, 2>::iterator I = Scavenged.begin(),
-       IE = Scavenged.end(); I != IE; ++I) {
-    if (I->Restore != MI)
-      continue;
-
-    I->Reg = 0;
-    I->Restore = NULL;
-  }
-
-  if (MI->isDebugValue())
-    return;
-
-  determineKillsAndDefs();
 
   // Verify uses and defs.
 #ifndef NDEBUG