diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -390,13 +390,19 @@
     CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=mcpu=") + CPU));
 
   if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
+    // The optimization level matches
+    // CompilerInvocation.cpp:getOptimizationLevel().
     StringRef OOpt;
     if (A->getOption().matches(options::OPT_O4) ||
         A->getOption().matches(options::OPT_Ofast))
       OOpt = "3";
-    else if (A->getOption().matches(options::OPT_O))
+    else if (A->getOption().matches(options::OPT_O)) {
       OOpt = A->getValue();
-    else if (A->getOption().matches(options::OPT_O0))
+      if (OOpt == "g")
+        OOpt = "1";
+      else if (OOpt == "s" || OOpt == "z")
+        OOpt = "2";
+    } else if (A->getOption().matches(options::OPT_O0))
       OOpt = "0";
     if (!OOpt.empty())
       CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=O") + OOpt));
diff --git a/clang/test/Driver/lto.c b/clang/test/Driver/lto.c
--- a/clang/test/Driver/lto.c
+++ b/clang/test/Driver/lto.c
@@ -48,6 +48,27 @@
 // RUN:   -fuse-ld=gold -flto -fno-lto -### 2>&1 | FileCheck --check-prefix=NO-LLVMGOLD %s
 // NO-LLVMGOLD-NOT: "-plugin" "{{.*}}{{[/\\]}}LLVMgold.{{dll|dylib|so}}"
 
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -O -### 2>&1 | FileCheck --check-prefix=O2 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -O1 -### 2>&1 | FileCheck --check-prefix=O1 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -Og -### 2>&1 | FileCheck --check-prefix=O1 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -O2 -### 2>&1 | FileCheck --check-prefix=O2 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -Os -### 2>&1 | FileCheck --check-prefix=O2 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -Oz -### 2>&1 | FileCheck --check-prefix=O2 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -O3 -### 2>&1 | FileCheck --check-prefix=O3 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -Ofast -### 2>&1 | FileCheck --check-prefix=O3 %s
+
+// O1: -plugin-opt=O1
+// O2: -plugin-opt=O2
+// O3: -plugin-opt=O3
+
 // -flto passes along an explicit debugger tuning argument.
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto -glldb 2> %t
 // RUN: FileCheck -check-prefix=CHECK-TUNING-LLDB < %t %s