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 +1118,39 @@
   return CI->getArgOperand(0);
 }
 
+Value *LibCallSimplifier::optimizeMemCCpy(CallInst *CI, IRBuilder<> &B) {
+  Value *Dst = CI->getArgOperand(0);
+  Value *Src = CI->getArgOperand(1);
+  Value *Size = CI->getArgOperand(3);
+  ConstantInt *StopChar = dyn_cast<ConstantInt>(CI->getArgOperand(2));
+  ConstantInt *N = dyn_cast<ConstantInt>(Size);
+  StringRef SrcStr;
+  if (CI->use_empty() && Dst == Src)
+    return Dst;
+  // memccpy(d, s, c, 0) -> nullptr
+  if (N && N->isNullValue())
+    return Constant::getNullValue(CI->getType());
+  if (!getConstantStringInfo(Src, SrcStr, /*Offset=*/0, /*TrimAtNul=*/false) || !StopChar)
+    return nullptr;
+
+  if (!N)
+    return nullptr;
+  size_t Pos = SrcStr.find(StopChar->getSExtValue());
+  if (Pos == StringRef::npos) {
+    if (N->getZExtValue() <= SrcStr.size()) {
+      B.CreateMemCpy(Dst, 1, Src, 1, Size);
+      return Constant::getNullValue(CI->getType());
+    }
+    return nullptr;
+  }
+
+  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 +2785,8 @@
       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
@@ -2,13 +2,17 @@
 ; RUN: opt < %s -instcombine -S | FileCheck %s
 
 @hello = private constant [11 x i8] c"helloworld\00", align 1
+@NoNulTerminator = private constant [10 x i8] c"helloworld", align 1
+@StopCharAfterNulTerminator = private constant [12 x i8] c"helloworld\00x", align 1
 
 declare i8* @memccpy(i8*, i8*, i32, i64)
 
 define i8* @memccpy_to_memcpy(i8* %dst) {
 ; CHECK-LABEL: @memccpy_to_memcpy(
-; 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 12)
-; CHECK-NEXT:    ret i8* [[CALL]]
+; 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
@@ -16,38 +20,95 @@
 
 define i8* @memccpy_to_memcpy2(i8* %dst) {
 ; CHECK-LABEL: @memccpy_to_memcpy2(
-; 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 5)
-; CHECK-NEXT:    ret i8* [[CALL]]
+; 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 5)
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 114, i64 8);
   ret i8* %call
 }
 
 define void @memccpy_to_memcpy3(i8* %dst) {
 ; CHECK-LABEL: @memccpy_to_memcpy3(
-; 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 5)
+; 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 111, i64 10) ; 111 is 'o'
+  ret void
+}
+
+define void @memccpy_to_memcpy4(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_memcpy4(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(11) [[DST:%.*]], i8* nonnull align 1 dereferenceable(11) getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i64 11, 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)
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 0, i64 12)
   ret void
 }
 
+define i8* @memccpy_to_memcpy5(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_memcpy5(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(7) [[DST:%.*]], i8* nonnull align 1 dereferenceable(7) getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i64 7, i1 false)
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, i8* [[DST]], i64 7
+; 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 7)
+  ret i8* %call
+}
+
+define i8* @memccpy_to_memcpy6(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_memcpy6(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(6) [[DST:%.*]], i8* nonnull align 1 dereferenceable(6) getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i64 6, i1 false)
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, i8* [[DST]], i64 6
+; 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 6);
+  ret i8* %call
+}
+
+define i8* @memccpy_to_memcpy7(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_memcpy7(
+; 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 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
+}
+
+define i8* @memccpy_to_memcpy8(i8* %dst) {
+; CHECK-LABEL: @memccpy_to_memcpy8(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(11) [[DST:%.*]], i8* nonnull align 1 dereferenceable(11) getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i64 11, i1 false)
+; 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 11) ; 115 is 's'
+  ret i8* %call
+}
+
+define i8* @memccpy_to_memcpy9(i8* %dst, i64 %n) {
+; CHECK-LABEL: @memccpy_to_memcpy9(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* nonnull align 1 dereferenceable(12) [[DST:%.*]], i8* nonnull align 1 dereferenceable(12) getelementptr inbounds ([12 x i8], [12 x i8]* @StopCharAfterNulTerminator, i64 0, i64 0), i64 12, i1 false)
+; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i8, i8* [[DST]], i64 12
+; CHECK-NEXT:    ret i8* [[TMP1]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([12 x i8], [12 x i8]* @StopCharAfterNulTerminator, i64 0, i64 0), i32 120, i64 15) ; 120 is 'x'
+  ret i8* %call
+}
+
 define i8* @memccpy_to_null(i8* %dst, i8* %src, i32 %c) {
 ; CHECK-LABEL: @memccpy_to_null(
-; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* [[SRC:%.*]], i32 [[C:%.*]], i64 0)
-; CHECK-NEXT:    ret i8* [[CALL]]
+; 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:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 115, i64 5)
-; CHECK-NEXT:    ret i8* [[CALL]]
+define void @memccpy_dst_src_same_retval_unused(i8* %dst, i32 %c, i64 %n) {
+; CHECK-LABEL: @memccpy_dst_src_same_retval_unused(
+; 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 115, i64 5) ; 115 is 's'
-  ret i8* %call
+  %call = call i8* @memccpy(i8* %dst, i8* %dst, i32 %c, i64 %n)
+  ret void
 }
 
 ; Negative tests
@@ -77,3 +138,48 @@
   %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
 }
+
+define i8* @no_nul_terminator(i8* %dst, i64 %n) {
+; CHECK-LABEL: @no_nul_terminator(
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* getelementptr inbounds ([12 x i8], [12 x i8]* @StopCharAfterNulTerminator, i64 0, i64 0), i32 120, i64 [[N:%.*]])
+; CHECK-NEXT:    ret i8* [[CALL]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([12 x i8], [12 x i8]* @StopCharAfterNulTerminator, i64 0, i64 0), i32 120, i64 %n) ; 120 is 'x'
+  ret i8* %call
+}
+
+define i8* @possibly_valid_data_after_array(i8* %dst, i64 %n) {
+; CHECK-LABEL: @possibly_valid_data_after_array(
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* getelementptr inbounds ([10 x i8], [10 x i8]* @NoNulTerminator, i64 0, i64 0), i32 115, i64 [[N:%.*]])
+; CHECK-NEXT:    ret i8* [[CALL]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* getelementptr inbounds ([10 x i8], [10 x i8]* @NoNulTerminator, i64 0, i64 0), i32 115, i64 %n) ; 115 is 's'
+  ret i8* %call
+}
+
+define i8* @possibly_valid_data_after_array2(i8* %dst, i64 %n) {
+; CHECK-LABEL: @possibly_valid_data_after_array2(
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 115, 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 115, i64 %n) ; 115 is 's'
+  ret i8* %call
+}
+
+define i8* @possibly_valid_data_after_array3(i8* %dst) {
+; CHECK-LABEL: @possibly_valid_data_after_array3(
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* getelementptr inbounds ([11 x i8], [11 x i8]* @hello, i64 0, i64 0), i32 115, 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 115, i64 12) ; 115 is 's'
+  ret i8* %call
+}
+
+define i8* @memccpy_dst_src_same_retval_used(i8* %dst, i32 %c, i64 %n) {
+; CHECK-LABEL: @memccpy_dst_src_same_retval_used(
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memccpy(i8* [[DST:%.*]], i8* [[DST]], i32 [[C:%.*]], i64 [[N:%.*]])
+; CHECK-NEXT:    ret i8* [[CALL]]
+;
+  %call = call i8* @memccpy(i8* %dst, i8* %dst, i32 %c, i64 %n)
+  ret i8* %call
+}