[Fuchsia] Rely on linker switch rather than dead code ref for profile runtime

[mcgrathr]

Summary

Follow the model used on Linux, where the clang driver passes the
linker a -u switch to force the profile runtime to be linked in,
rather than having every TU emit a dead function with a reference.

[phosek]

LGTM

llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp

1036–1037

Nit: s/for linux/for Linux or Fuchsia/

[mcgrathr]

comment update

[MaskRay]

clang/lib/Driver/ToolChains/Fuchsia.cpp

372

Thanks. I just realized Linux::addProfileRTLibs can be simplified.

clang/lib/Driver/ToolChains/Fuchsia.h

public:
   }
 
   std::string ComputeEffectiveClangTriple(const llvm::opt::ArgList &Args,
                                           types::ID InputType) const override;
 
   SanitizerMask getSupportedSanitizers() const override;
   SanitizerMask getDefaultSanitizers() const override;
 
+  void addProfileRTLibs(const llvm::opt::ArgList &Args,
+                        llvm::opt::ArgStringList &CmdArgs) const override;
+
   RuntimeLibType
   GetRuntimeLibType(const llvm::opt::ArgList &Args) const override;
   CXXStdlibType
   GetCXXStdlibType(const llvm::opt::ArgList &Args) const override;
 
   void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                              llvm::opt::ArgStringList &CC1Args,
                              Action::OffloadKind DeviceOffloadKind) const override;

clang/lib/Driver/ToolChains/Fuchsia.cpp

 #include "CommonArgs.h"
 #include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Driver.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
 using namespace clang::driver;
 using namespace clang::driver::toolchains;
 using namespace clang::driver::tools;
 using namespace clang;
case llvm::Triple::x86_64:
     Res |= SanitizerKind::SafeStack;
     break;
   default:
     // TODO: Enable SafeStack on RISC-V once tested.
     break;
   }
   return Res;
 }
+
+void Fuchsia::addProfileRTLibs(const llvm::opt::ArgList &Args,
+                               llvm::opt::ArgStringList &CmdArgs) const {
+  // Add linker option -u__llvm_profile_runtime to cause runtime
+  // initialization module to be linked in.
+  if (needsProfileRT(Args))
+    CmdArgs.push_back(Args.MakeArgString(
+        Twine("-u", llvm::getInstrProfRuntimeHookVarName())));
+  ToolChain::addProfileRTLibs(Args, CmdArgs);
+}

clang/test/Driver/fuchsia.c

 // CHECK-THINLTO: "-plugin-opt=mcpu=x86-64"
 // CHECK-THINLTO: "-plugin-opt=thinlto"
 // CHECK-THINLTO: "-plugin-opt=jobs=8"
 
 // RUN: %clang %s -### --target=x86_64-fuchsia \
 // RUN:     -gsplit-dwarf -c %s 2>&1 \
 // RUN:     | FileCheck %s -check-prefix=CHECK-SPLIT-DWARF
 // CHECK-SPLIT-DWARF: "-split-dwarf-output" "fuchsia.dwo"
+
+// RUN: %clang %s -### --target=aarch64-fuchsia \
+// RUN:     -fprofile-instr-generate -fcoverage-mapping \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:     -fuse-ld=lld 2>&1 \
+// RUN:     | FileCheck %s -check-prefix=CHECK-PROFRT-AARCH64
+// CHECK-PROFRT-AARCH64: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
+// CHECK-PROFRT-AARCH64: "-u__llvm_profile_runtime"
+// CHECK-PROFRT-AARCH64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}aarch64-fuchsia{{/|\\\\}}libclang_rt.profile.a"
+
+// RUN: %clang %s -### --target=x86_64-fuchsia \
+// RUN:     -fprofile-instr-generate -fcoverage-mapping \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:     -fuse-ld=lld 2>&1 \
+// RUN:     | FileCheck %s -check-prefix=CHECK-PROFRT-X86_64
+// CHECK-PROFRT-X86_64: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
+// CHECK-PROFRT-X86_64: "-u__llvm_profile_runtime"
+// CHECK-PROFRT-X86_64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}libclang_rt.profile.a"

llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp

auto *NamesRegisterF =
                          getInstrProfNamesRegFuncName(), M);
     IRB.CreateCall(NamesRegisterF, {IRB.CreateBitCast(NamesVar, VoidPtrTy),
                                     IRB.getInt64(NamesSize)});
   }
 
   IRB.CreateRetVoid();
 }
 
 bool InstrProfiling::emitRuntimeHook() {
-  // We expect the linker to be invoked with -u<hook_var> flag for linux,
-  // for which case there is no need to emit the user function.
-  if (TT.isOSLinux())
+  // We expect the linker to be invoked with -u<hook_var> flag for Linux or
+  // Fuchsia, in which case there is no need to emit the user function.
+  if (TT.isOSLinux() || TT.isOSFuchsia())
     return false;
 
   // If the module's provided its own runtime, we don't need to do anything.
   if (M->getGlobalVariable(getInstrProfRuntimeHookVarName()))
     return false;
 
   // Declare an external variable that will pull in the runtime initialization.
   auto *Int32Ty = Type::getInt32Ty(M->getContext());

llvm/test/Instrumentation/InstrProfiling/linkage.ll

 ;; Check that runtime symbols get appropriate linkage.
 
 ; RUN: opt < %s -mtriple=x86_64-apple-macosx10.10.0 -instrprof -S | FileCheck %s --check-prefixes=POSIX,MACHO
 ; RUN: opt < %s -mtriple=x86_64-unknown-linux -instrprof -S | FileCheck %s --check-prefixes=POSIX,LINUX
+; RUN: opt < %s -mtriple=x86_64-unknown-fuchsia -instrprof -S | FileCheck %s --check-prefixes=POSIX,LINUX
 ; RUN: opt < %s  -mtriple=x86_64-pc-win32-coff -instrprof -S | FileCheck %s --check-prefixes=COFF
 ; RUN: opt < %s -mtriple=x86_64-apple-macosx10.10.0 -passes=instrprof -S | FileCheck %s --check-prefixes=POSIX,MACHO
 ; RUN: opt < %s -mtriple=x86_64-unknown-linux -passes=instrprof -S | FileCheck %s --check-prefixes=POSIX,LINUX
+; RUN: opt < %s -mtriple=x86_64-unknown-fuchsia -passes=instrprof -S | FileCheck %s --check-prefixes=POSIX,LINUX
 ; RUN: opt < %s  -mtriple=x86_64-pc-win32-coff -passes=instrprof -S | FileCheck %s --check-prefixes=COFF
 
 ; MACHO: @__llvm_profile_runtime = external global i32
 ; LINUX-NOT: @__llvm_profile_runtime = external global i32
 
 @__profn_foo = hidden constant [3 x i8] c"foo"
 @__profn_foo_weak = weak hidden constant [8 x i8] c"foo_weak"
 @"__profn_linkage.ll:foo_internal" = internal constant [23 x i8] c"linkage.ll:foo_internal"