[Driver] Fall back to plain '-plugin LLVMgold.so' if no lib at std path

[mgorny]

Summary

Add a fallback to using plain '-plugin LLVMgold.so' when the plugin does
not exist at the standard path. This e.g. happens on Gentoo when clang
is compiled for a different ABI than binutils.

Since full path is used to reference LLVMgold.so, it is safe to use
the same path to check whether the plugin exists. If it does not, this
lets gold perform library search instead of passing known-wrong path.
As a result, the plugin is either found somewhere in search path, or
gold fails the same.

This is an alternate solution to the problem originally addressed by
D23754. Unlike the original proposal, it does not introduce additional
options that could confuse users and does not affect anything in common
installations.

lib/Driver/Tools.cpp

 //===--- Tools.cpp - Tools Implementations ----------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "Tools.h"
 #include "InputInfo.h"
 #include "ToolChains.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/ObjCRuntime.h"
 #include "clang/Basic/Version.h"
+#include "clang/Basic/VirtualFileSystem.h"
 #include "clang/Config/config.h"
 #include "clang/Driver/Action.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Job.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"

 
 static void AddGoldPlugin(const ToolChain &ToolChain, const ArgList &Args,
                           ArgStringList &CmdArgs, bool IsThinLTO,
                           const Driver &D) {
   // Tell the linker to load the plugin. This has to come before AddLinkerInputs
   // as gold requires -plugin to come before any -plugin-opt that -Wl might
   // forward.
   CmdArgs.push_back("-plugin");
+  // Try the full path first. However, if the file does not exist, just let gold
+  // fall back to regular library lookup instead of passing a known-invalid
+  // path. This is meant to fix non-standard Gentoo install of LLVMgold.so
+  // plugin.
   std::string Plugin =
       ToolChain.getDriver().Dir + "/../lib" CLANG_LIBDIR_SUFFIX "/LLVMgold.so";
+  if (!D.getVFS().exists(Plugin))
+    Plugin = "LLVMgold.so";
   CmdArgs.push_back(Args.MakeArgString(Plugin));
 
   // Try to pass driver level flags relevant to LTO code generation down to
   // the plugin.
 
   // Handle flags for selecting CPU variants.
   std::string CPU = getCPUName(Args, ToolChain.getTriple());
   if (!CPU.empty())

test/Driver/gold-lto.c

 // RUN: touch %t.o
 //
 // RUN: %clang -target x86_64-unknown-linux -### %t.o -flto 2>&1 \
 // RUN:     -Wl,-plugin-opt=foo -O3 \
 // RUN:     | FileCheck %s --check-prefix=CHECK-X86-64-BASIC
-// CHECK-X86-64-BASIC: "-plugin" "{{.*}}/LLVMgold.so"
+// CHECK-X86-64-BASIC: "-plugin" "{{.*}}LLVMgold.so"
 // CHECK-X86-64-BASIC: "-plugin-opt=O3"
 // CHECK-X86-64-BASIC: "-plugin-opt=foo"
 //
 // RUN: %clang -target x86_64-unknown-linux -### %t.o -flto 2>&1 \
 // 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" "{{.*}}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:     | FileCheck %s --check-prefix=CHECK-ARM-V7A
-// CHECK-ARM-V7A: "-plugin" "{{.*}}/LLVMgold.so"
+// 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=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"
+// CHECK-X86-ANDROID: "-plugin" "{{.*}}LLVMgold.so"

test/Driver/lto.c

 
 // RUN: not %clang %s -emit-llvm 2>&1 | FileCheck --check-prefix=LLVM-LINK %s
 // LLVM-LINK: -emit-llvm cannot be used when linking
 
 // -flto should cause link using gold plugin
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto 2> %t
 // RUN: FileCheck -check-prefix=CHECK-LINK-LTO-ACTION < %t %s
 //
-// CHECK-LINK-LTO-ACTION: "-plugin" "{{.*}}/LLVMgold.so"
+// CHECK-LINK-LTO-ACTION: "-plugin" "{{.*}}LLVMgold.so"
 
 // -flto=full should cause link using gold plugin
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto=full 2> %t
 // RUN: FileCheck -check-prefix=CHECK-LINK-FULL-ACTION < %t %s
 //
-// CHECK-LINK-FULL-ACTION: "-plugin" "{{.*}}/LLVMgold.so"
+// CHECK-LINK-FULL-ACTION: "-plugin" "{{.*}}LLVMgold.so"
 
 // Check that subsequent -fno-lto takes precedence
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto=full -fno-lto 2> %t
 // RUN: FileCheck -check-prefix=CHECK-LINK-NOLTO-ACTION < %t %s
 //
-// CHECK-LINK-NOLTO-ACTION-NOT: "-plugin" "{{.*}}/LLVMgold.so"
+// CHECK-LINK-NOLTO-ACTION-NOT: "-plugin" "{{.*}}LLVMgold.so"
 
 // -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
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto -g 2> %t
 // RUN: FileCheck -check-prefix=CHECK-NO-TUNING < %t %s
 //
 // CHECK-TUNING-LLDB:   "-plugin-opt=-debugger-tune=lldb"
 // CHECK-NO-TUNING-NOT: "-plugin-opt=-debugger-tune

test/Driver/thinlto.c

 // CHECK-COMPILELINK-ACTIONS: 3: backend, {2}, lto-bc
 // CHECK-COMPILELINK-ACTIONS: 4: linker, {3}, image
 
 // -flto=thin should cause link using gold plugin with thinlto option,
 // also confirm that it takes precedence over earlier -fno-lto and -flto=full.
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto=full -fno-lto -flto=thin 2> %t
 // RUN: FileCheck -check-prefix=CHECK-LINK-THIN-ACTION < %t %s
 //
-// CHECK-LINK-THIN-ACTION: "-plugin" "{{.*}}/LLVMgold.so"
+// CHECK-LINK-THIN-ACTION: "-plugin" "{{.*}}LLVMgold.so"
 // CHECK-LINK-THIN-ACTION: "-plugin-opt=thinlto"
 
 // Check that subsequent -flto=full takes precedence
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto=thin -flto=full 2> %t
 // RUN: FileCheck -check-prefix=CHECK-LINK-FULL-ACTION < %t %s
 //
-// CHECK-LINK-FULL-ACTION: "-plugin" "{{.*}}/LLVMgold.so"
+// CHECK-LINK-FULL-ACTION: "-plugin" "{{.*}}LLVMgold.so"
 // CHECK-LINK-FULL-ACTION-NOT: "-plugin-opt=thinlto"
 
 // Check that subsequent -fno-lto takes precedence
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto=thin -fno-lto 2> %t
 // RUN: FileCheck -check-prefix=CHECK-LINK-NOLTO-ACTION < %t %s
 //
-// CHECK-LINK-NOLTO-ACTION-NOT: "-plugin" "{{.*}}/LLVMgold.so"
+// CHECK-LINK-NOLTO-ACTION-NOT: "-plugin" "{{.*}}LLVMgold.so"
 // CHECK-LINK-NOLTO-ACTION-NOT: "-plugin-opt=thinlto"