Index: include/llvm/Transforms/Utils/SimplifyLibCalls.h
===================================================================
--- include/llvm/Transforms/Utils/SimplifyLibCalls.h
+++ include/llvm/Transforms/Utils/SimplifyLibCalls.h
@@ -175,6 +175,7 @@
   Value *optimizeMemCmp(CallInst *CI, IRBuilder<> &B);
   Value *optimizeBCmp(CallInst *CI, IRBuilder<> &B);
   Value *optimizeMemCmpBCmpCommon(CallInst *CI, IRBuilder<> &B);
+  Value *optimizeMemCCpy(CallInst *CI, IRBuilder<> &B);
   Value *optimizeMemPCpy(CallInst *CI, IRBuilder<> &B);
   Value *optimizeMemCpy(CallInst *CI, IRBuilder<> &B);
   Value *optimizeMemMove(CallInst *CI, IRBuilder<> &B);
Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1118,6 +1118,32 @@
   return CI->getArgOperand(0);
 }
 
+Value *LibCallSimplifier::optimizeMemCCpy(CallInst *CI, IRBuilder<> &B) {
+  Value *Dst = CI->getArgOperand(0);
+  Value *Src = CI->getArgOperand(1);
+  ConstantInt *StopChar = dyn_cast<ConstantInt>(CI->getArgOperand(2));
+  ConstantInt *N = dyn_cast<ConstantInt>(CI->getArgOperand(3));
+  StringRef SrcStr;
+  if (!N)
+    return nullptr;
+  // memccpy(d, s, c, 0) -> nullptr
+  if (N->isNullValue())
+    return Constant::getNullValue(CI->getType());
+  if (!getConstantStringInfo(Src, SrcStr) || !StopChar)
+    return nullptr;
+
+  size_t Pos = SrcStr.find(StopChar->getSExtValue());
+  if (Pos == StringRef::npos)
+  // memccpy(d, s, c, 0) and c not in s -> nullptr
+    return Constant::getNullValue(CI->getType());
+
+  Value *NewN =
+      ConstantInt::get(N->getType(), std::min(Pos + 1, N->getZExtValue()));
+  // memccpy -> llvm.memcpy
+  B.CreateMemCpy(Dst, 1, Src, 1, NewN);
+  return B.CreateInBoundsGEP(B.getInt8Ty(), Dst, NewN);
+}
+
 Value *LibCallSimplifier::optimizeMemPCpy(CallInst *CI, IRBuilder<> &B) {
   Value *Dst = CI->getArgOperand(0);
   Value *N = CI->getArgOperand(2);
@@ -2752,6 +2778,8 @@
       return optimizeMemCmp(CI, Builder);
     case LibFunc_memcpy:
       return optimizeMemCpy(CI, Builder);
+    case LibFunc_memccpy:
+      return optimizeMemCCpy(CI, Builder);
     case LibFunc_mempcpy:
       return optimizeMemPCpy(CI, Builder);
     case LibFunc_memmove:
Index: test/Transforms/InstCombine/memccpy.ll
===================================================================
--- test/Transforms/InstCombine/memccpy.ll
+++ test/Transforms/InstCombine/memccpy.ll
@@ -0,0 +1,80 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+@hello = private constant [11 x i8] c"helloworld\00", align 1
+
+declare i8* @memccpy(i8*, i8*, i32, i64)
+
+define i8* @memccpy_to_memcpy(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_memcpy(
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast i8* [[DST:%.*]] to i64*
+; CHECK-NEXT:    store i64 8245940763182785896, i64* [[TMP1]], align 1
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i8, i8* [[DST]], i64 8
+; CHECK-NEXT:    ret i8* [[TMP2]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 114, i64 12) ; 114 is 'r'
+  ret i8* %call
+}
+
+define i8* @memccpy_to_memcpy2(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_memcpy2(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(5) [[DST:%.*]], i8* nonnull align 1 dereferenceable(5) getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i64 5, i1 false)
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, i8* [[DST]], i64 5
+; CHECK-NEXT:    ret i8* [[TMP1]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 114, i64 5)
+  ret i8* %call
+}
+
+define void @memccpy_to_memcpy3(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_memcpy3(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(5) [[DST:%.*]], i8* nonnull align 1 dereferenceable(5) getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i64 5, i1 false)
+; CHECK-NEXT:    ret void
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 114, i64 5)
+  ret void
+}
+
+define i8* @memccpy_to_null(i8* %dst, i8* %src, i32 %c) {
+; CHECK-LABEL: @memccpy_to_null(
+; CHECK-NEXT:    ret i8* null
+;
+  %call = call i8* @memccpy(i8* %dst, i8* %src, i32 %c, i64 0)
+  ret i8* %call
+}
+
+define i8* @memccpy_to_null2(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_null2(
+; CHECK-NEXT:    ret i8* null
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 115, i64 5) ; 115 is 's'
+  ret i8* %call
+}
+
+; Negative tests
+define i8* @unknown_src(i8* %dst, i8* %src) {
+; CHECK-LABEL: @unknown_src(
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* [[SRC:%.*]], i32 114, i64 12)
+; CHECK-NEXT:    ret i8* [[CALL]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* %src, i32 114, i64 12)
+  ret i8* %call
+}
+
+define i8* @unknown_stop_char(i8* %dst, i32 %c) {
+; CHECK-LABEL: @unknown_stop_char(
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 [[C:%.*]], i64 12)
+; CHECK-NEXT:    ret i8* [[CALL]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 %c, i64 12)
+  ret i8* %call
+}
+
+define i8* @unknown_size_n(i8* %dst, i64 %n) {
+; CHECK-LABEL: @unknown_size_n(
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 114, i64 [[N:%.*]])
+; CHECK-NEXT:    ret i8* [[CALL]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 114, i64 %n)
+  ret i8* %call
+}