[Gold] Pass -mllvm options to the gold plugin

[jmolloy]

Summary

The gold plugin can take LLVM options, but the syntax is confusing: -Wl,-plugin-opt= or -Xlinker -plugin-opt=.

Instead, pass -mllvm options through to Gold so the obvious syntax works.

[• rafael]

Maybe. I would like a second opinion on this one. The potential issue
I see is that we are using compiler options during linking. Normally
they are just ignored. Is it surprising if LTO starts using them?

Cheers,
Rafael

[jmolloy]

Abandoning - this isn't as clear-cut as I thought.

lib/Driver/Tools.cpp

if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
     else if (A->getOption().matches(options::OPT_O0))
       OOpt = "0";
     if (!OOpt.empty())
       CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=O") + OOpt));
   }
 
   if (IsThinLTO)
     CmdArgs.push_back("-plugin-opt=thinlto");
+
+  // Claim and pass through -mllvm options to the Gold plugin.
+  for (const Arg *A : Args.filtered(options::OPT_mllvm)) {
+    A->claim();
+    CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=") + A->getValue(0)));
+  }
 }
 
 /// This is a helper function for validating the optional refinement step
 /// parameter in reciprocal argument strings. Return false if there is an error
 /// parsing the refinement step. Otherwise, return true and set the Position
 /// of the refinement step in the input string.
 static bool getRefinementStep(StringRef In, const Driver &D,
                               const Arg &A, size_t &Position) {

test/Driver/gold-lto.c

 // RUN:     -march=corei7 -Wl,-plugin-opt=foo -Ofast \
 // RUN:     | FileCheck %s --check-prefix=CHECK-X86-64-COREI7
 // CHECK-X86-64-COREI7: "-plugin" "{{.*}}/LLVMgold.so"
 // CHECK-X86-64-COREI7: "-plugin-opt=mcpu=corei7"
 // CHECK-X86-64-COREI7: "-plugin-opt=O3"
 // CHECK-X86-64-COREI7: "-plugin-opt=foo"
 //
 // RUN: %clang -target arm-unknown-linux -### %t.o -flto 2>&1 \
-// RUN:     -march=armv7a -Wl,-plugin-opt=foo -O0 \
+// RUN:     -march=armv7a -Wl,-plugin-opt=foo -O0 -mllvm -bar=baz \
+// RUN:     -mllvm -test-option \
 // RUN:     | FileCheck %s --check-prefix=CHECK-ARM-V7A
 // CHECK-ARM-V7A: "-plugin" "{{.*}}/LLVMgold.so"
 // CHECK-ARM-V7A: "-plugin-opt=mcpu=cortex-a8"
 // CHECK-ARM-V7A: "-plugin-opt=O0"
+// CHECK-ARM-V7A: "-plugin-opt=-bar=baz"
+// CHECK-ARM-V7A: "-plugin-opt=-test-option"
 // CHECK-ARM-V7A: "-plugin-opt=foo"
 //
 // RUN: %clang -target i686-linux-android -### %t.o -flto 2>&1 \
 // RUN:     | FileCheck %s --check-prefix=CHECK-X86-ANDROID
 // CHECK-X86-ANDROID: "-plugin" "{{.*}}/LLVMgold.so"