Index: include/llvm/Transforms/Utils/SimplifyLibCalls.h
===================================================================
--- include/llvm/Transforms/Utils/SimplifyLibCalls.h
+++ include/llvm/Transforms/Utils/SimplifyLibCalls.h
@@ -150,6 +150,8 @@
   Value *optimizeIsDigit(CallInst *CI, IRBuilder<> &B);
   Value *optimizeIsAscii(CallInst *CI, IRBuilder<> &B);
   Value *optimizeToAscii(CallInst *CI, IRBuilder<> &B);
+  Value *optimizeAtoi(CallInst *CI, IRBuilder<> &B);
+  Value *optimizeStrtol(CallInst *CI, IRBuilder<> &B);
 
   // Formatting and IO Library Call Optimizations
   Value *optimizeErrorReporting(CallInst *CI, IRBuilder<> &B,
Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1677,6 +1677,30 @@
                      ConstantInt::get(CI->getType(), 0x7F));
 }
 
+Value *LibCallSimplifier::optimizeAtoi(CallInst *CI, IRBuilder<> &B) {
+  StringRef Str;
+  if (!getConstantStringInfo(CI->getArgOperand(0), Str))
+    return nullptr;
+
+  return ConstantInt::get(CI->getType(), atoi(Str.str().c_str()));
+}
+
+Value *LibCallSimplifier::optimizeStrtol(CallInst *CI, IRBuilder<> &B) {
+  StringRef Str;
+  if (!getConstantStringInfo(CI->getArgOperand(0), Str))
+    return nullptr;
+
+  if (!match(CI->getArgOperand(1), m_Zero())) {
+    return nullptr;
+  }
+
+  if (ConstantInt *CInt = dyn_cast<ConstantInt>(CI->getArgOperand(2)))
+    return ConstantInt::get(CI->getType(), strtol(Str.str().c_str(), nullptr,
+                                                  CInt->getSExtValue()));
+
+  return nullptr;
+}
+
 //===----------------------------------------------------------------------===//
 // Formatting and IO Library Call Optimizations
 //===----------------------------------------------------------------------===//
@@ -2271,6 +2295,10 @@
       return optimizeIsAscii(CI, Builder);
     case LibFunc_toascii:
       return optimizeToAscii(CI, Builder);
+    case LibFunc_atoi:
+      return optimizeAtoi(CI, Builder);
+    case LibFunc_strtol:
+      return optimizeStrtol(CI, Builder);
     case LibFunc_printf:
       return optimizePrintF(CI, Builder);
     case LibFunc_sprintf:
Index: test/Transforms/InstCombine/str-int.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/str-int.ll
@@ -0,0 +1,38 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+@.str = private unnamed_addr constant [3 x i8] c"12\00", align 1
+
+define i32 @strtol_1() #0 {
+; CHECK-LABEL: @strtol_1(
+; CHECK-NEXT:    ret i32 12
+;
+  %call = call i64 @strtol(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i32 0, i32 0), i8** null, i32 10) #3
+  %conv = trunc i64 %call to i32
+  ret i32 %conv
+}
+
+; Function Attrs: nounwind
+declare i64 @strtol(i8*, i8**, i32) #1
+
+; Function Attrs: noinline nounwind uwtable
+define i32 @strtol_2() #0 {
+; CHECK-LABEL: @strtol_2(
+; CHECK-NEXT:    ret i32 18
+;
+  %call = call i64 @strtol(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i32 0, i32 0), i8** null, i32 16) #3
+  %conv = trunc i64 %call to i32
+  ret i32 %conv
+}
+
+; Function Attrs: noinline nounwind uwtable
+define i32 @atoi_test() #0 {
+; CHECK-LABEL: @atoi_test(
+; CHECK-NEXT:    ret i32 12
+;
+  %call = call i32 @atoi(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i32 0, i32 0)) #4
+  ret i32 %call
+}
+
+; Function Attrs: nounwind readonly
+declare i32 @atoi(i8*) #2