Index: llvm/include/llvm/LTO/Config.h
===================================================================
--- llvm/include/llvm/LTO/Config.h
+++ llvm/include/llvm/LTO/Config.h
@@ -55,6 +55,7 @@
   CodeGenOpt::Level CGOptLevel = CodeGenOpt::Default;
   CodeGenFileType CGFileType = CGFT_ObjectFile;
   unsigned OptLevel = 2;
+  unsigned SizeLevel = 0;
   bool DisableVerify = false;
 
   /// Use the new pass manager
Index: llvm/lib/LTO/LTOBackend.cpp
===================================================================
--- llvm/lib/LTO/LTOBackend.cpp
+++ llvm/lib/LTO/LTOBackend.cpp
@@ -311,7 +311,7 @@
   PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM->getTargetTriple()));
   if (Conf.Freestanding)
     PMB.LibraryInfo->disableAllFunctions();
-  PMB.Inliner = createFunctionInliningPass();
+  PMB.Inliner = createFunctionInliningPass(Conf.OptLevel, Conf.SizeLevel, false);
   PMB.ExportSummary = ExportSummary;
   PMB.ImportSummary = ImportSummary;
   // Unconditionally verify input since it is not verified before this
Index: llvm/lib/LTO/LTOCodeGenerator.cpp
===================================================================
--- llvm/lib/LTO/LTOCodeGenerator.cpp
+++ llvm/lib/LTO/LTOCodeGenerator.cpp
@@ -185,6 +185,10 @@
 }
 
 void LTOCodeGenerator::setOptLevel(unsigned Level) {
+  if (Level > 3) {
+    Config.SizeLevel = Level - 3;
+    Level = 2;
+  }
   Config.OptLevel = Level;
   Config.PTO.LoopVectorization = Config.OptLevel > 1;
   Config.PTO.SLPVectorization = Config.OptLevel > 1;
Index: llvm/tools/lto/lto.cpp
===================================================================
--- llvm/tools/lto/lto.cpp
+++ llvm/tools/lto/lto.cpp
@@ -152,8 +152,12 @@
   LTOCodeGenerator *CG = unwrap(cg);
   CG->setAttrs(codegen::getMAttrs());
 
-  if (OptLevel < '0' || OptLevel > '3')
-    report_fatal_error("Optimization level must be between 0 and 3");
+  if (OptLevel == 's')
+    OptLevel = '4';
+  else if (OptLevel == 'z')
+    OptLevel = '5';
+  if (OptLevel < '0' || OptLevel > '5')
+    report_fatal_error("Optimization level must be between 0 and 3 or Os or Oz");
   CG->setOptLevel(OptLevel - '0');
   CG->setFreestanding(EnableFreestanding);
   CG->setDisableVerify(DisableVerify);
@@ -521,8 +525,12 @@
   CodeGen->setFreestanding(EnableFreestanding);
 
   if (OptLevel.getNumOccurrences()) {
-    if (OptLevel < '0' || OptLevel > '3')
-      report_fatal_error("Optimization level must be between 0 and 3");
+    if (OptLevel == 's')
+      OptLevel = '4';
+    else if (OptLevel == 'z')
+      OptLevel = '5';
+    if (OptLevel < '0' || OptLevel > '5')
+      report_fatal_error("Optimization level must be between 0 and 3 or Os or Oz");
     CodeGen->setOptLevel(OptLevel - '0');
     switch (OptLevel) {
     case '0':