Index: include/llvm/Transforms/Utils/SimplifyLibCalls.h
===================================================================
--- include/llvm/Transforms/Utils/SimplifyLibCalls.h
+++ include/llvm/Transforms/Utils/SimplifyLibCalls.h
@@ -124,6 +124,8 @@
   Value *optimizePrintFString(CallInst *CI, IRBuilder<> &B);
   Value *optimizeSPrintFString(CallInst *CI, IRBuilder<> &B);
   Value *optimizeFPrintFString(CallInst *CI, IRBuilder<> &B);
+  bool isFortifiedCallFoldable(CallInst *CI, unsigned SizeCIOp,
+                               unsigned SizeArgOp, bool isString);
 
   /// hasFloatVersion - Checks if there is a float version of the specified
   /// function by checking for an existing function with name FuncName + f
Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -18,6 +18,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/Triple.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DiagnosticInfo.h"
@@ -120,25 +121,41 @@
 // Fortified Library Call Optimizations
 //===----------------------------------------------------------------------===//
 
-static bool isFortifiedCallFoldable(CallInst *CI, unsigned SizeCIOp, unsigned SizeArgOp,
-                       bool isString) {
-  if (CI->getArgOperand(SizeCIOp) == CI->getArgOperand(SizeArgOp))
+bool LibCallSimplifier::isFortifiedCallFoldable(CallInst *CI, unsigned SizeCIOp,
+                                                unsigned SizeArgOp,
+                                                bool isString) {
+  // The destination operand is always the first.
+  Value *Dest = CI->getArgOperand(0);
+  Value *SizeCIVal = CI->getArgOperand(SizeCIOp);
+  Value *SizeArg = CI->getArgOperand(SizeArgOp);
+
+  // If the argument size and known object size are the same value, we can
+  // remove the check.
+  if (SizeCIVal == SizeArg)
     return true;
-  if (ConstantInt *SizeCI =
-          dyn_cast<ConstantInt>(CI->getArgOperand(SizeCIOp))) {
-    if (SizeCI->isAllOnesValue())
-      return true;
-    if (isString) {
-      uint64_t Len = GetStringLength(CI->getArgOperand(SizeArgOp));
-      // If the length is 0 we don't know how long it is and so we can't
-      // remove the check.
-      if (Len == 0)
-        return false;
-      return SizeCI->getZExtValue() >= Len;
-    }
-    if (ConstantInt *Arg = dyn_cast<ConstantInt>(CI->getArgOperand(SizeArgOp)))
-      return SizeCI->getZExtValue() >= Arg->getZExtValue();
+
+  uint64_t ObjectSizeInt = 0;
+  APInt SizeCIAPInt = APInt::getAllOnesValue(64U);
+
+  if (ConstantInt *SizeCI = dyn_cast<ConstantInt>(SizeCIVal))
+    SizeCIAPInt = SizeCI->getValue();
+  else if (getObjectSize(Dest, ObjectSizeInt, DL, TLI))
+    SizeCIAPInt = APInt(64U, ObjectSizeInt);
+
+  // If the object size is unknown (-1), we can remove the check.
+  if (SizeCIAPInt.isAllOnesValue())
+    return true;
+  if (isString) {
+    uint64_t Len = GetStringLength(SizeArg);
+    // If the length is 0 we don't know how long it is and so we can't
+    // remove the check.
+    if (Len == 0)
+      return false;
+    return SizeCIAPInt.getZExtValue() >= Len;
   }
+  // If the libcall is known not to overflow, we can remove the check.
+  if (ConstantInt *Arg = dyn_cast<ConstantInt>(SizeArg))
+    return SizeCIAPInt.getZExtValue() >= Arg->getZExtValue();
   return false;
 }
 
Index: test/CodeGen/X86/2011-02-21-VirtRegRewriter-KillSubReg.ll
===================================================================
--- test/CodeGen/X86/2011-02-21-VirtRegRewriter-KillSubReg.ll
+++ test/CodeGen/X86/2011-02-21-VirtRegRewriter-KillSubReg.ll
@@ -25,7 +25,7 @@
   %call782 = call i8* @__memmove_chk(i8* %add.ptr768, i8* undef, i32 %call747, i32 undef)
   br label %cond.end791
 
-; CHECK: calll __memmove_chk
+; CHECK: calll memmove@PLT
 cond.false783:
   %call.i1035 = call i8* @__memmove_chk(i8* %add.ptr768, i8* undef, i32 %call747, i32 undef) nounwind
   br label %cond.end791
Index: test/Transforms/InstCombine/stpcpy_chk-1.ll
===================================================================
--- test/Transforms/InstCombine/stpcpy_chk-1.ll
+++ test/Transforms/InstCombine/stpcpy_chk-1.ll
@@ -60,7 +60,7 @@
   %dst = getelementptr inbounds [60 x i8]* @a, i32 0, i32 0
   %src = getelementptr inbounds [12 x i8]* @.str, i32 0, i32 0
 
-; CHECK: @__memcpy_chk
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i32
   %len = call i32 @llvm.objectsize.i32.p0i8(i8* %dst, i1 false)
   %ret = call i8* @__stpcpy_chk(i8* %dst, i8* %src, i32 %len)
 ; CHECK: ret i8* getelementptr inbounds ([60 x i8]* @a, i32 0, i32 11)
Index: test/Transforms/InstCombine/strcpy_chk-1.ll
===================================================================
--- test/Transforms/InstCombine/strcpy_chk-1.ll
+++ test/Transforms/InstCombine/strcpy_chk-1.ll
@@ -60,7 +60,7 @@
   %dst = getelementptr inbounds [60 x i8]* @a, i32 0, i32 0
   %src = getelementptr inbounds [12 x i8]* @.str, i32 0, i32 0
 
-; CHECK: @__memcpy_chk
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i32
   %len = call i32 @llvm.objectsize.i32.p0i8(i8* %dst, i1 false)
   call i8* @__strcpy_chk(i8* %dst, i8* %src, i32 %len)
   ret void