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 +311,8 @@
   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/test/tools/lto/lto_optsize.ll
===================================================================
--- /dev/null
+++ llvm/test/tools/lto/lto_optsize.ll
@@ -0,0 +1,51 @@
+; RUN: llvm-as %s -o %t.o
+
+; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -dylib -arch x86_64 -macosx_version_min 10.10.0 -o %t.dylib %t.o -save-temps  -undefined dynamic_lookup -exported_symbol inner -exported_symbol outer -exported_symbol outer2 -exported_symbol extern -exported_symbol a -mllvm -Os
+; RUN: llvm-dis %t.dylib.lto.opt.bc -o - | FileCheck --check-prefix=OS %s
+
+; RUN: %ld64 -lto_library %llvmshlibdir/libLTO.dylib -dylib -arch x86_64 -macosx_version_min 10.10.0 -o %t.dylib %t.o -save-temps  -undefined dynamic_lookup -exported_symbol inner -exported_symbol outer -exported_symbol outer2 -exported_symbol extern -exported_symbol a -mllvm -Oz
+; RUN: llvm-dis %t.dylib.lto.opt.bc -o - | FileCheck --check-prefix=OZ %s
+
+; The inline threshold for a function with the optsize attribute is currently
+; the same as the global inline threshold for -Os. Check that the optsize
+; function attribute doesn't alter the function-specific inline threshold if the
+; global inline threshold is lower (as for -Oz).
+
+target triple = "x86_64-apple-macosx10.8.0"
+
+@a = global i32 4
+
+; This function should be larger than the inline threshold for -Oz (25), but
+; smaller than the inline threshold for optsize (75).
+define i32 @inner() {
+  call void @extern()
+  %a1 = load volatile i32, i32* @a
+  %x1 = add i32 %a1,  %a1
+  %a2 = load volatile i32, i32* @a
+  %x2 = add i32 %x1, %a2
+  %a3 = load volatile i32, i32* @a
+  %x3 = add i32 %x2, %a3
+  %a4 = load volatile i32, i32* @a
+  %x4 = add i32 %x3, %a4
+  %a5 = load volatile i32, i32* @a
+  %x5 = add i32 %x3, %a5
+  ret i32 %x5
+}
+
+; @inner() should be inlined for -Os but not for -Oz.
+; OZ: call
+; OS-NOT: call
+define i32 @outer() optsize {
+   %r = call i32 @inner()
+   ret i32 %r
+}
+
+; @inner() should not be inlined for -Os and -Oz.
+; OZ: call
+; OS: call
+define i32 @outer2() minsize {
+   %r = call i32 @inner()
+   ret i32 %r
+}
+
+declare void @extern()
Index: llvm/tools/lto/lto.cpp
===================================================================
--- llvm/tools/lto/lto.cpp
+++ llvm/tools/lto/lto.cpp
@@ -152,8 +152,13 @@
   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 +526,13 @@
   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':