diff --git a/llvm/lib/Analysis/MemoryLocation.cpp b/llvm/lib/Analysis/MemoryLocation.cpp
--- a/llvm/lib/Analysis/MemoryLocation.cpp
+++ b/llvm/lib/Analysis/MemoryLocation.cpp
@@ -247,6 +247,21 @@
         return MemoryLocation(Arg, LocationSize::precise(LenCI->getZExtValue()),
                               AATags);
       break;
+    case LibFunc_memchr:
+      assert((ArgIdx == 0) && "Invalid argument index for memchr");
+      if (const ConstantInt *LenCI =
+              dyn_cast<ConstantInt>(Call->getArgOperand(2)))
+        return MemoryLocation(Arg, LocationSize::precise(LenCI->getZExtValue()),
+                              AATags);
+      break;
+    case LibFunc_memccpy:
+      assert((ArgIdx == 0 || ArgIdx == 1) &&
+             "Invalid argument index for memccpy");
+      if (const ConstantInt *LenCI =
+              dyn_cast<ConstantInt>(Call->getArgOperand(3)))
+        return MemoryLocation(Arg, LocationSize::precise(LenCI->getZExtValue()),
+                              AATags);
+      break;
     default:
       break;
     };
diff --git a/llvm/test/Analysis/BasicAA/libfuncs.ll b/llvm/test/Analysis/BasicAA/libfuncs.ll
--- a/llvm/test/Analysis/BasicAA/libfuncs.ll
+++ b/llvm/test/Analysis/BasicAA/libfuncs.ll
@@ -86,3 +86,43 @@
   store i8 3, i8* %b.gep.5
   ret i32 %res
 }
+
+declare i8* @memchr(i8*, i32, i64)
+
+; CHECK-LABEL: Function: test_memchr_const_size
+; CHECK: Just Ref:  Ptr: i8* %res      <->  %res = call i8* @memchr(i8* %a, i32 42, i64 4)
+; CHECK-NEXT: Just Ref:  Ptr: i8* %a.gep.1  <->  %res = call i8* @memchr(i8* %a, i32 42, i64 4)
+; CHECK-NEXT: NoModRef:  Ptr: i8* %a.gep.5  <->  %res = call i8* @memchr(i8* %a, i32 42, i64 4)
+define i8* @test_memchr_const_size(i8* noalias %a) {
+entry:
+  %res = call i8* @memchr(i8* %a, i32 42, i64 4)
+  %a.gep.1 = getelementptr i8, i8* %a, i32 1
+  store i8 0, i8* %a.gep.1
+  %a.gep.5 = getelementptr i8, i8* %a, i32 5
+  store i8 1, i8* %a.gep.5
+  ret i8* %res
+}
+
+declare i8* @memccpy(i8*, i8*, i32, i64)
+
+; CHECK-LABEL: Function: test_memccpy_const_size
+; CHECK:      Both ModRef:  Ptr: i8* %a     <->  %res = call i8* @memccpy(i8* %a, i8* %b, i32 42, i64 4)
+; CHECK-NEXT: Just Ref:  Ptr: i8* %b        <->  %res = call i8* @memccpy(i8* %a, i8* %b, i32 42, i64 4)
+; CHECK-NEXT: Both ModRef:  Ptr: i8* %res   <->  %res = call i8* @memccpy(i8* %a, i8* %b, i32 42, i64 4)
+; CHECK-NEXT: Both ModRef:  Ptr: i8* %a.gep.1       <->  %res = call i8* @memccpy(i8* %a, i8* %b, i32 42, i64 4)
+; CHECK-NEXT: NoModRef:  Ptr: i8* %a.gep.5  <->  %res = call i8* @memccpy(i8* %a, i8* %b, i32 42, i64 4)
+; CHECK-NEXT: Just Ref:  Ptr: i8* %b.gep.1  <->  %res = call i8* @memccpy(i8* %a, i8* %b, i32 42, i64 4)
+; CHECK-NEXT: NoModRef:  Ptr: i8* %b.gep.5  <->  %res = call i8* @memccpy(i8* %a, i8* %b, i32 42, i64 4)
+define i8* @test_memccpy_const_size(i8* noalias %a, i8* noalias %b) {
+entry:
+  %res = call i8* @memccpy(i8* %a, i8* %b, i32 42, i64 4)
+  %a.gep.1 = getelementptr i8, i8* %a, i32 1
+  store i8 0, i8* %a.gep.1
+  %a.gep.5 = getelementptr i8, i8* %a, i32 5
+  store i8 1, i8* %a.gep.5
+  %b.gep.1 = getelementptr i8, i8* %b, i32 1
+  store i8 2, i8* %b.gep.1
+  %b.gep.5 = getelementptr i8, i8* %b, i32 5
+  store i8 3, i8* %b.gep.5
+  ret i8* %res
+}
diff --git a/llvm/test/Transforms/DeadStoreElimination/MSSA/libcalls.ll b/llvm/test/Transforms/DeadStoreElimination/MSSA/libcalls.ll
--- a/llvm/test/Transforms/DeadStoreElimination/MSSA/libcalls.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/MSSA/libcalls.ll
@@ -190,3 +190,115 @@
   %res = icmp eq i32 %call, 0
   ret i1 %res
 }
+
+declare i8* @memchr(i8*, i32, i64)
+
+define i8* @test_memchr_const_size() {
+; CHECK-LABEL: @test_memchr_const_size(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[STACK:%.*]] = alloca [10 x i8], align 1
+; CHECK-NEXT:    [[STACK_PTR:%.*]] = bitcast [10 x i8]* [[STACK]] to i8*
+; CHECK-NEXT:    store i8 49, i8* [[STACK_PTR]], align 1
+; CHECK-NEXT:    [[GEP_1:%.*]] = getelementptr i8, i8* [[STACK_PTR]], i64 1
+; CHECK-NEXT:    store i8 50, i8* [[GEP_1]], align 1
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memchr(i8* [[STACK_PTR]], i32 42, i64 2)
+; CHECK-NEXT:    ret i8* [[CALL]]
+;
+entry:
+  %stack = alloca [10 x i8]
+  %stack.ptr = bitcast [10 x i8]* %stack to i8*
+  store i8 49, i8* %stack.ptr, align 1
+  %gep.1 = getelementptr i8, i8* %stack.ptr, i64 1
+  store i8 50, i8* %gep.1, align 1
+  %gep.2 = getelementptr i8, i8* %stack.ptr, i64 2
+  store i8 51, i8* %gep.2, align 1
+  %gep.3 = getelementptr i8, i8* %stack.ptr, i64 3
+  store i8 52, i8* %gep.3, align 1
+  %call = call i8* @memchr(i8* %stack.ptr, i32 42, i64 2)
+  ret i8* %call
+}
+
+define i8* @test_memchr_variable_size(i64 %n) {
+; CHECK-LABEL: @test_memchr_variable_size(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[STACK:%.*]] = alloca [10 x i8], align 1
+; CHECK-NEXT:    [[STACK_PTR:%.*]] = bitcast [10 x i8]* [[STACK]] to i8*
+; CHECK-NEXT:    store i8 49, i8* [[STACK_PTR]], align 1
+; CHECK-NEXT:    [[GEP_1:%.*]] = getelementptr i8, i8* [[STACK_PTR]], i64 1
+; CHECK-NEXT:    store i8 50, i8* [[GEP_1]], align 1
+; CHECK-NEXT:    [[GEP_2:%.*]] = getelementptr i8, i8* [[STACK_PTR]], i64 2
+; CHECK-NEXT:    store i8 51, i8* [[GEP_2]], align 1
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i8, i8* [[STACK_PTR]], i64 4
+; CHECK-NEXT:    store i8 52, i8* [[GEP]], align 1
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @memchr(i8* [[STACK_PTR]], i32 42, i64 [[N:%.*]])
+; CHECK-NEXT:    ret i8* [[CALL]]
+;
+entry:
+  %stack = alloca [10 x i8]
+  %stack.ptr = bitcast [10 x i8]* %stack to i8*
+  store i8 49, i8* %stack.ptr, align 1
+  %gep.1 = getelementptr i8, i8* %stack.ptr, i64 1
+  store i8 50, i8* %gep.1, align 1
+  %gep.2 = getelementptr i8, i8* %stack.ptr, i64 2
+  store i8 51, i8* %gep.2, align 1
+  %gep = getelementptr i8, i8* %stack.ptr, i64 4
+  store i8 52, i8* %gep, align 1
+  %call = call i8* @memchr(i8* %stack.ptr, i32 42, i64 %n)
+  ret i8* %call
+}
+
+declare i8* @memccpy(i8*, i8*, i32, i64)
+
+define i8* @test_memccpy_const_size(i8* %foo) {
+; CHECK-LABEL: @test_memccpy_const_size(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[STACK:%.*]] = alloca [10 x i8], align 1
+; CHECK-NEXT:    [[STACK_PTR:%.*]] = bitcast [10 x i8]* [[STACK]] to i8*
+; CHECK-NEXT:    store i8 49, i8* [[STACK_PTR]], align 1
+; CHECK-NEXT:    [[GEP_1:%.*]] = getelementptr i8, i8* [[STACK_PTR]], i64 1
+; CHECK-NEXT:    store i8 50, i8* [[GEP_1]], align 1
+; CHECK-NEXT:    [[RES:%.*]] = call i8* @memccpy(i8* [[FOO:%.*]], i8* [[STACK_PTR]], i32 42, i64 2)
+; CHECK-NEXT:    ret i8* [[RES]]
+;
+entry:
+  %stack = alloca [10 x i8]
+  %stack.ptr = bitcast [10 x i8]* %stack to i8*
+  store i8 49, i8* %stack.ptr, align 1
+  %gep.1 = getelementptr i8, i8* %stack.ptr, i64 1
+  store i8 50, i8* %gep.1, align 1
+  %gep.2 = getelementptr i8, i8* %stack.ptr, i64 2
+  store i8 51, i8* %gep.2, align 1
+  %gep.3 = getelementptr i8, i8* %stack.ptr, i64 3
+  store i8 52, i8* %gep.3, align 1
+  %res = call i8* @memccpy(i8* %foo, i8* %stack.ptr, i32 42, i64 2)
+  ret i8* %res
+}
+
+define i8* @test_memccpy_variable_size(i8* %foo, i64 %n) {
+; CHECK-LABEL: @test_memccpy_variable_size(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[STACK:%.*]] = alloca [10 x i8], align 1
+; CHECK-NEXT:    [[STACK_PTR:%.*]] = bitcast [10 x i8]* [[STACK]] to i8*
+; CHECK-NEXT:    store i8 49, i8* [[STACK_PTR]], align 1
+; CHECK-NEXT:    [[GEP_1:%.*]] = getelementptr i8, i8* [[STACK_PTR]], i64 1
+; CHECK-NEXT:    store i8 50, i8* [[GEP_1]], align 1
+; CHECK-NEXT:    [[GEP_2:%.*]] = getelementptr i8, i8* [[STACK_PTR]], i64 2
+; CHECK-NEXT:    store i8 51, i8* [[GEP_2]], align 1
+; CHECK-NEXT:    [[GEP_3:%.*]] = getelementptr i8, i8* [[STACK_PTR]], i64 3
+; CHECK-NEXT:    store i8 52, i8* [[GEP_3]], align 1
+; CHECK-NEXT:    [[RES:%.*]] = call i8* @memccpy(i8* [[FOO:%.*]], i8* [[STACK_PTR]], i32 42, i64 [[N:%.*]])
+; CHECK-NEXT:    ret i8* [[RES]]
+;
+entry:
+  %stack = alloca [10 x i8]
+  %stack.ptr = bitcast [10 x i8]* %stack to i8*
+  store i8 49, i8* %stack.ptr, align 1
+  %gep.1 = getelementptr i8, i8* %stack.ptr, i64 1
+  store i8 50, i8* %gep.1, align 1
+  %gep.2 = getelementptr i8, i8* %stack.ptr, i64 2
+  store i8 51, i8* %gep.2, align 1
+  %gep.3 = getelementptr i8, i8* %stack.ptr, i64 3
+  store i8 52, i8* %gep.3, align 1
+  %res = call i8* @memccpy(i8* %foo, i8* %stack.ptr, i32 42, i64 %n)
+  ret i8* %res
+}