diff --git a/lib/CodeGen/CriticalAntiDepBreaker.cpp b/lib/CodeGen/CriticalAntiDepBreaker.cpp
index 7b2ce362417..f79598de1d9 100644
--- a/lib/CodeGen/CriticalAntiDepBreaker.cpp
+++ b/lib/CodeGen/CriticalAntiDepBreaker.cpp
@@ -325,17 +325,55 @@ void CriticalAntiDepBreaker::ScanInstruction(MachineInstr *MI,
   }
 }
 
-// Check all machine instructions that define the antidependent register.
-// Return true if any of these instructions define the new register.
+// Check all machine operands that reference the antidependent register and must
+// be replaced by NewReg. Return true if any of their parent instructions may
+// clobber the new register.
+//
+// Note: AntiDepReg may be referenced by a two-address instruction such that
+// it's use operand is tied to a def operand. We guard against the case in which
+// the two-address instruction also defines NewReg, as may happen with
+// pre/postincrement loads. In this case, both the use and def operands are in
+// RegRefs because the def is inserted by PrescanInstruction and not erased
+// during ScanInstruction. So checking for an instructions with definitions of
+// both NewReg and AntiDepReg covers it.
 bool
-CriticalAntiDepBreaker::isNewRegModifiedByRefs(RegRefIter RegRefBegin,
-                                               RegRefIter RegRefEnd,
-                                               unsigned NewReg)
+CriticalAntiDepBreaker::isNewRegClobberedByRefs(RegRefIter RegRefBegin,
+                                                RegRefIter RegRefEnd,
+                                                unsigned NewReg)
 {
   for (RegRefIter I = RegRefBegin; I != RegRefEnd; ++I ) {
-    MachineOperand *MO = I->second;
-    if (MO->getParent()->modifiesRegister(NewReg, TRI))
+    MachineOperand *RefOper = I->second;
+
+    // Don't allow the instruction defining AntiDepReg to earlyclobber its
+    // operands, in case they may be assigned to NewReg. In this case antidep
+    // breaking must fail, but it's too rare to bother optimizing.
+    if (RefOper->isDef() && RefOper->isEarlyClobber())
       return true;
+
+    // Handle cases in which this instructions defines NewReg.
+    MachineInstr *MI = RefOper->getParent();
+    for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+      const MachineOperand &CheckOper = MI->getOperand(i);
+
+      if (!CheckOper.isReg() || !CheckOper.isDef() ||
+          CheckOper.getReg() != NewReg)
+        continue;
+
+      // Don't allow the instruction to define NewReg and AntiDepReg.
+      // When AntiDepReg is renamed it will be an illegal op.
+      if (RefOper->isDef())
+        return true;
+
+      // Don't allow an instruction using AntiDepReg to be earlyclobbered by
+      // NewReg
+      if (CheckOper.isEarlyClobber())
+        return true;
+
+      // Don't allow inline asm to define NewReg at all. Who know what it's
+      // doing with it.
+      if (MI->isInlineAsm())
+        return true;
+    }
   }
   return false;
 }
@@ -361,7 +399,7 @@ CriticalAntiDepBreaker::findSuitableFreeRegister(RegRefIter RegRefBegin,
     // If any instructions that define AntiDepReg also define the NewReg, it's
     // not suitable.  For example, Instruction with multiple definitions can
     // result in this condition.
-    if (isNewRegModifiedByRefs(RegRefBegin, RegRefEnd, NewReg)) continue;
+    if (isNewRegClobberedByRefs(RegRefBegin, RegRefEnd, NewReg)) continue;
     // If NewReg is dead and NewReg's most recent def is not before
     // AntiDepReg's kill, it's safe to replace AntiDepReg with NewReg.
     assert(((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u))
diff --git a/lib/CodeGen/CriticalAntiDepBreaker.h b/lib/CodeGen/CriticalAntiDepBreaker.h
index df21ef28340..6adc45add6d 100644
--- a/lib/CodeGen/CriticalAntiDepBreaker.h
+++ b/lib/CodeGen/CriticalAntiDepBreaker.h
@@ -92,9 +92,9 @@ class TargetRegisterInfo;
   private:
     void PrescanInstruction(MachineInstr *MI);
     void ScanInstruction(MachineInstr *MI, unsigned Count);
-    bool isNewRegModifiedByRefs(RegRefIter RegRefBegin,
-                                RegRefIter RegRefEnd,
-                                unsigned NewReg);
+    bool isNewRegClobberedByRefs(RegRefIter RegRefBegin,
+                                 RegRefIter RegRefEnd,
+                                 unsigned NewReg);
     unsigned findSuitableFreeRegister(RegRefIter RegRefBegin,
                                       RegRefIter RegRefEnd,
                                       unsigned AntiDepReg,