[AArch64][Clang][Linux] Enable out-of-line atomics by default.

Generate outline atomics if compiling for armv8-a non-LSE AArch64 Linux
(including Android) targets to use LSE instructions, if they are available,
at runtime. Library support is checked by clang driver which doesn't enable
outline atomics if no proper libraries (libgcc >= 9.3.1 or compiler-rt) found.

Differential Revision: https://reviews.llvm.org/D93585

clang/include/clang/Driver/ToolChain.h

@@ -456,6 +456,12 @@ public:
   /// by default.
   virtual bool IsUnwindTablesDefault(const llvm::opt::ArgList &Args) const;
 
+  /// Test whether this toolchain supports outline atomics by default.
+  virtual bool
+  IsAArch64OutlineAtomicsDefault(const llvm::opt::ArgList &Args) const {
+    return false;
+  }
+
   /// Test whether this toolchain defaults to PIC.
   virtual bool isPICDefault() const = 0;
 

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6500,6 +6500,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
       CmdArgs.push_back("-target-feature");
       CmdArgs.push_back("-outline-atomics");
     }
+  } else if (Triple.isAArch64() &&
+             getToolChain().IsAArch64OutlineAtomicsDefault(Args)) {
+    CmdArgs.push_back("-target-feature");
+    CmdArgs.push_back("+outline-atomics");
   }
 
   if (Args.hasFlag(options::OPT_faddrsig, options::OPT_fno_addrsig,

clang/lib/Driver/ToolChains/Linux.cpp

@@ -836,6 +836,19 @@ bool Linux::isPIEDefault() const {
           getTriple().isMusl() || getSanitizerArgs().requiresPIE();
 }
 
+bool Linux::IsAArch64OutlineAtomicsDefault(const ArgList &Args) const {
+  // Outline atomics for AArch64 are supported by compiler-rt
+  // and libgcc since 9.3.1
+  assert(getTriple().isAArch64() && "expected AArch64 target!");
+  ToolChain::RuntimeLibType RtLib = GetRuntimeLibType(Args);
+  if (RtLib == ToolChain::RLT_CompilerRT)
+    return true;
+  assert(RtLib == ToolChain::RLT_Libgcc && "unexpected runtime library type!");
+  if (GCCInstallation.getVersion().isOlderThan(9, 3, 1))
+    return false;
+  return true;
+}
+
 bool Linux::isNoExecStackDefault() const {
     return getTriple().isAndroid();
 }

clang/lib/Driver/ToolChains/Linux.h

@@ -36,6 +36,8 @@ public:
   void AddIAMCUIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                            llvm::opt::ArgStringList &CC1Args) const override;
   CXXStdlibType GetDefaultCXXStdlibType() const override;
+  bool
+  IsAArch64OutlineAtomicsDefault(const llvm::opt::ArgList &Args) const override;
   bool isPIEDefault() const override;
   bool isNoExecStackDefault() const override;
   bool IsMathErrnoDefault() const override;

clang/test/Driver/aarch64-features.c

@@ -6,3 +6,60 @@
 // The AArch64 PCS states that chars should be unsigned.
 // CHECK: fno-signed-char
 
+// Check for AArch64 out-of-line atomics default settings.
+// RUN: %clang -target aarch64-linux-android -rtlib=compiler-rt \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-ON %s
+
+// RUN: %clang -target aarch64-linux-gnu -rtlib=compiler-rt \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-ON %s
+
+// RUN: %clang -target arm64-unknown-linux -rtlib=compiler-rt \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-ON %s
+
+// RUN: %clang -target aarch64--none-eabi -rtlib=compiler-rt \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-OFF %s
+
+// RUN: %clang -target aarch64-apple-darwin -rtlib=compiler-rt \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-OFF %s
+
+// RUN: %clang -target aarch64-windows-gnu -rtlib=compiler-rt \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-OFF %s
+
+// RUN: %clang -target aarch64-unknown-openbsd -rtlib=compiler-rt \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-OFF %s
+
+// RUN: %clang -target aarch64-linux-gnu -rtlib=libgcc \
+// RUN: --gcc-toolchain=%S/Inputs/aarch64-linux-gnu-tree/gcc-10 \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-ON %s
+
+// RUN: %clang -target aarch64-linux-gnu -rtlib=libgcc \
+// RUN: --gcc-toolchain=%S/Inputs/aarch64-linux-gnu-tree/gcc-7.5.0 \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-OFF %s
+
+// RUN: %clang -target aarch64-linux-gnu -rtlib=libgcc \
+// RUN: --gcc-toolchain=%S/Inputs/aarch64-linux-gnu-tree/gcc-9.3.1 \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-ON %s
+
+// RUN: %clang -target aarch64-linux-gnu -rtlib=libgcc \
+// RUN: --gcc-toolchain=%S/Inputs/aarch64-linux-gnu-tree/gcc-9.3.0 \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-OFF %s
+
+// RUN: %clang -target arm64-linux -rtlib=compiler-rt -mno-outline-atomics \
+// RUN: -### -c %s 2>&1 | FileCheck \
+// RUN: -check-prefixes=CHECK-OUTLINE-ATOMICS-OFF,CHECK-NO-OUTLINE-ATOMICS %s
+
+// RUN: %clang -target aarch64-linux-gnu -rtlib=libgcc -mno-outline-atomics \
+// RUN: --gcc-toolchain=%S/Inputs/aarch64-linux-gnu-tree/gcc-10 \
+// RUN: -### -c %s 2>&1 | FileCheck \
+// RUN: -check-prefixes=CHECK-OUTLINE-ATOMICS-OFF,CHECK-NO-OUTLINE-ATOMICS %s
+
+// RUN: %clang -target aarch64-apple-darwin -rtlib=compiler-rt -moutline-atomics \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-ON %s
+
+// RUN: %clang -target aarch64-windows-gnu -rtlib=libgcc -moutline-atomics \
+// RUN: --gcc-toolchain=%S/Inputs/aarch64-linux-gnu-tree/gcc-7.5.0 \
+// RUN: -### -c %s 2>&1 | FileCheck -check-prefix=CHECK-OUTLINE-ATOMICS-ON %s
+
+// CHECK-OUTLINE-ATOMICS-ON: "-target-feature" "+outline-atomics"
+// CHECK-OUTLINE-ATOMICS-OFF-NOT: "-target-feature" "+outline-atomics"
+// CHECK-NO-OUTLINE-ATOMICS: "-target-feature" "-outline-atomics"