Correctly support -shared-libgcc.

[saugustine]

Summary

Correctly support -shared-libgcc.

[echristo]

LGTM.

-eric

[saugustine]

Committed with r350900.

lib/Driver/ToolChains/CommonArgs.cpp

 static void AddLibgcc(const llvm::Triple &Triple, const Driver &D,
                       ArgStringList &CmdArgs, const ArgList &Args) {
   bool isAndroid = Triple.isAndroid();
   bool isCygMing = Triple.isOSCygMing();
   bool IsIAMCU = Triple.isOSIAMCU();
   bool StaticLibgcc = Args.hasArg(options::OPT_static_libgcc) ||
                       Args.hasArg(options::OPT_static);
 
-  // The driver ignores -shared-libgcc and therefore treats such cases as
-  // unspecified.  Breaking out the two variables as below makes the current
-  // behavior explicit.
-  bool UnspecifiedLibgcc = !StaticLibgcc;
-  bool SharedLibgcc = !StaticLibgcc;
+  bool SharedLibgcc = Args.hasArg(options::OPT_shared_libgcc);
+  bool UnspecifiedLibgcc = !StaticLibgcc && !SharedLibgcc;
 
   // Gcc adds libgcc arguments in various ways:
   //
   // gcc <none>: -lgcc --as-needed -lgcc_s --no-as-needed
   // g++ <none>:                   -lgcc_s               -lgcc
   // gcc shared:                   -lgcc_s               -lgcc
   // g++ shared:                   -lgcc_s               -lgcc
   // gcc static: -lgcc             -lgcc_eh
   // g++ static: -lgcc             -lgcc_eh
   //
   // Also, certain targets need additional adjustments.
 
   bool LibGccFirst = (D.CCCIsCC() && UnspecifiedLibgcc) || StaticLibgcc;
   if (LibGccFirst)
     CmdArgs.push_back("-lgcc");
 
-  bool AsNeeded = D.CCCIsCC() && !StaticLibgcc && !isAndroid && !isCygMing;
+  bool AsNeeded = D.CCCIsCC() && UnspecifiedLibgcc && !isAndroid && !isCygMing;
   if (AsNeeded)
     CmdArgs.push_back("--as-needed");
 
   if ((UnspecifiedLibgcc || SharedLibgcc) && !isAndroid)
     CmdArgs.push_back("-lgcc_s");
 
   else if (StaticLibgcc && !isAndroid && !IsIAMCU)
     CmdArgs.push_back("-lgcc_eh");

test/Driver/linux-ld.c

 // CHECK-CLANG-STATIC-LIBGCC-DYNAMIC: "-lc"
 // CHECK-CLANG-STATIC-LIBGCC-DYNAMIC: "-lgcc" "-lgcc_eh"
 //
 // RUN: %clang -shared-libgcc -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=x86_64-unknown-linux -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-CLANG-SHARED-LIBGCC %s
-// CHECK-CLANG-SHARED-LIBGCC: warning: argument unused during compilation: '-shared-libgcc'
-// This will be the correct check once the driver supports -shared-libgcc
-// SKIP-CHECK-CLANG-SHARED-LIBGCC: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
-// SKIP-CHECK-CLANG-SHARED-LIBGCC: "-lgcc_s" "-lgcc"
-// SKIP-CHECK-CLANG-SHARED-LIBGCC: "-lc"
-// SKIP-CHECK-CLANG-SHARED-LIBGCC: "-lgcc_s" "-lgcc"
+// CHECK-CLANG-SHARED-LIBGCC: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
+// CHECK-CLANG-SHARED-LIBGCC: "-lgcc_s" "-lgcc"
+// CHECK-CLANG-SHARED-LIBGCC: "-lc"
+// CHECK-CLANG-SHARED-LIBGCC: "-lgcc_s" "-lgcc"
 //
 // RUN: %clang -shared-libgcc -dynamic -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=x86_64-unknown-linux -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-CLANG-SHARED-LIBGCC-DYNAMIC %s
-// CHECK-CLANG-SHARED-LIBGCC-DYNAMIC: warning: argument unused during compilation: '-shared-libgcc'
-// CHECK-CLANG-SHARED-LIBGCC-DYNAMIC: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
-// This will be the correct check once the driver supports -shared-libgcc
-// SKIP-CHECK-CLANG-SHARED-LIBGCC-DYNAMIC: "-lgcc_s" "-lgcc"
-// SKIP-CHECK-CLANG-SHARED-LIBGCC-DYNAMIC: "-lc"
-// SKIP-CHECK-CLANG-SHARED-LIBGCC-DYNAMIC: "-lgcc_s" "-lgcc"
+// CHECK-CLANG-SHARED-LIBGCC-DYNAMIC: "-lgcc_s" "-lgcc"
+// CHECK-CLANG-SHARED-LIBGCC-DYNAMIC: "-lc"
+// CHECK-CLANG-SHARED-LIBGCC-DYNAMIC: "-lgcc_s" "-lgcc"
 //
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     --target=aarch64-linux-android -rtlib=platform \
 // RUN:     --gcc-toolchain="" \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \
 // RUN:   | FileCheck --check-prefix=CHECK-CLANG-ANDROID-NONE %s
 // CHECK-CLANG-ANDROID-NONE: "{{.*}}ld{{(.exe)?}}" "--sysroot=[[SYSROOT:[^"]+]]"
 // CHECK-CLANG-ANDROID-NONE: "-lgcc" "-ldl" "-lc"