[PGO][AIX] Improve dummy var retention and allow -bcdtors:csect linking.

1) Use a static array of pointer to retain the dummy vars.
2) Associate liveness of the array with that of the runtime hook variable
   __llvm_profile_runtime.
3) Perform the runtime initialization through the runtime hook variable.
4) Preserve the runtime hook variable using the -u linker flag.

Reviewed By: hubert.reinterpretcast

Differential Revision: https://reviews.llvm.org/D136192

Author: Wael Yehia

clang/lib/Driver/ToolChains/AIX.cpp

@@ -13,6 +13,7 @@
 #include "clang/Driver/Options.h"
 #include "clang/Driver/SanitizerArgs.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/Path.h"
 
 using AIX = clang::driver::toolchains::AIX;
@@ -348,6 +349,16 @@ void AIX::AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
   llvm_unreachable("Unexpected C++ library type; only libc++ is supported.");
 }
 
+void AIX::addProfileRTLibs(const llvm::opt::ArgList &Args,
+                           llvm::opt::ArgStringList &CmdArgs) const {
+  // Add linker option -u__llvm_profile_runtime to cause runtime
+  // initialization to occur.
+  if (needsProfileRT(Args))
+    CmdArgs.push_back(Args.MakeArgString(
+        Twine("-u", llvm::getInstrProfRuntimeHookVarName())));
+  ToolChain::addProfileRTLibs(Args, CmdArgs);
+}
+
 ToolChain::CXXStdlibType AIX::GetDefaultCXXStdlibType() const {
   return ToolChain::CST_Libcxx;
 }

clang/lib/Driver/ToolChains/AIX.h

@@ -80,6 +80,9 @@ class LLVM_LIBRARY_VISIBILITY AIX : public ToolChain {
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
 
+  void addProfileRTLibs(const llvm::opt::ArgList &Args,
+                        llvm::opt::ArgStringList &CmdArgs) const override;
+
   CXXStdlibType GetDefaultCXXStdlibType() const override;
 
   RuntimeLibType GetDefaultRuntimeLibType() const override;

compiler-rt/lib/profile/InstrProfilingPlatformLinux.c

@@ -250,23 +250,21 @@ void __llvm_profile_register_names_function(void *NamesStart,
 // section exists. So for the scenario where the user objects have no such
 // section (i.e. when they are compiled with -fno-profile-generate), we always
 // define these zero length variables in each of the above 4 sections.
-COMPILER_RT_VISIBILITY int dummy_cnts[0] COMPILER_RT_SECTION(
+static int dummy_cnts[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_CNTS_SECT_NAME);
-COMPILER_RT_VISIBILITY int dummy_data[0] COMPILER_RT_SECTION(
+static int dummy_data[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_DATA_SECT_NAME);
-COMPILER_RT_VISIBILITY const int dummy_name[0] COMPILER_RT_SECTION(
+static const int dummy_name[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_NAME_SECT_NAME);
-COMPILER_RT_VISIBILITY int dummy_vnds[0] COMPILER_RT_SECTION(
+static int dummy_vnds[0] COMPILER_RT_SECTION(
     COMPILER_RT_SEG INSTR_PROF_VNODES_SECT_NAME);
 
-// Create a fake reference to avoid GC'ing of the dummy variables by the linker.
-// Ideally, we create a ".ref" of each variable inside the function
-// __llvm_profile_begin_counters(), but there's no source level construct
-// that allows us to generate that.
-__attribute__((destructor)) void keep() {
-  int volatile use = &dummy_cnts < &dummy_data && &dummy_name < &dummy_vnds;
-  (void)use;
-}
+// To avoid GC'ing of the dummy variables by the linker, reference them in an
+// array and reference the array in the runtime registration code
+// (InstrProfilingRuntime.cpp)
+COMPILER_RT_VISIBILITY
+void *__llvm_profile_keep[] = {(void *)&dummy_cnts, (void *)&dummy_data,
+                               (void *)&dummy_name, (void *)&dummy_vnds};
 #endif
 
 #endif

compiler-rt/lib/profile/InstrProfilingRuntime.cpp

@@ -10,19 +10,23 @@ extern "C" {
 
 #include "InstrProfiling.h"
 
-/* int __llvm_profile_runtime  */
-COMPILER_RT_VISIBILITY int INSTR_PROF_PROFILE_RUNTIME_VAR;
+static int RegisterRuntime() {
+  __llvm_profile_initialize();
+  return 0;
 }
 
-namespace {
-
-class RegisterRuntime {
-public:
-  RegisterRuntime() {
-    __llvm_profile_initialize();
-  }
-};
-
-RegisterRuntime Registration;
+#ifndef _AIX
+/* int __llvm_profile_runtime  */
+COMPILER_RT_VISIBILITY int INSTR_PROF_PROFILE_RUNTIME_VAR;
 
+static int Registration = RegisterRuntime();
+#else
+extern COMPILER_RT_VISIBILITY void *__llvm_profile_keep[];
+/* On AIX, when linking with -bcdtors:csect, the variable whose constructor does
+ * the registration needs to be explicitly kept, hence we reuse the runtime hook
+ * variable to do the registration since it'll be kept via the -u linker flag.
+ * Create a volatile reference to __llvm_profile_keep to keep the array alive.*/
+COMPILER_RT_VISIBILITY int INSTR_PROF_PROFILE_RUNTIME_VAR =
+    ((void)*(void *volatile *)__llvm_profile_keep, RegisterRuntime());
+#endif
 }

compiler-rt/test/profile/AIX/lit.local.cfg.py

@@ -0,0 +1,9 @@
+def getRoot(config):
+  if not config.parent:
+    return config
+  return getRoot(config.parent)
+
+root = getRoot(config)
+
+if root.host_os not in ['AIX']:
+  config.unsupported = True

compiler-rt/test/profile/AIX/shared-bexpall-pgo.c

@@ -0,0 +1,14 @@
+// RUN: split-file %s %t
+// RUN: cd %t
+//
+// RUN: %clang_pgogen foo.c -c -o foo.o
+// RUN: %clang_pgogen -shared foo.o -o libfoo.so -bexpall
+// RUN: %clang_pgogen -L%t user.c libfoo.so -o user1
+// RUN: ./user1
+
+//--- foo.c
+void foo() {}
+
+//--- user.c
+void foo();
+int main() { foo(); }

llvm/lib/Transforms/Instrumentation/InstrProfiling.cpp

@@ -1199,7 +1199,7 @@ void InstrProfiling::emitRegistration() {
 bool InstrProfiling::emitRuntimeHook() {
   // We expect the linker to be invoked with -u<hook_var> flag for Linux
   // in which case there is no need to emit the external variable.
-  if (TT.isOSLinux())
+  if (TT.isOSLinux() || TT.isOSAIX())
     return false;
 
   // If the module's provided its own runtime, we don't need to do anything.

llvm/test/Instrumentation/InstrProfiling/no-counters.ll

@@ -2,7 +2,7 @@
 
 ; RUN: opt < %s -mtriple=x86_64-apple-macosx10.10.0 -passes=instrprof -S | FileCheck %s -check-prefixes=ALL,DARWIN
 ; RUN: opt < %s -mtriple=x86_64-linux-unknown -passes=instrprof -S | FileCheck %s -check-prefixes=ALL,LINUX
-; RUN: opt < %s -mtriple=powerpc64-ibm-aix-xcoff -passes=instrprof -S | FileCheck %s -check-prefixes=ALL,DARWIN
+; RUN: opt < %s -mtriple=powerpc64-ibm-aix-xcoff -passes=instrprof -S | FileCheck %s -check-prefixes=ALL,LINUX
 ; ALL-NOT: @__profc
 ; ALL-NOT: @__profd
 ; DARWIN: @__llvm_profile_runtime

llvm/test/Instrumentation/InstrProfiling/profiling.ll

@@ -13,7 +13,7 @@
 ; MACHO: @__llvm_profile_runtime = external hidden global i32
 ; ELF_GENERIC: @__llvm_profile_runtime = external hidden global i32
 ; ELF-NOT: @__llvm_profile_runtime = external global i32
-; XCOFF: @__llvm_profile_runtime = external hidden global i32
+; XCOFF-NOT: @__llvm_profile_runtime = external hidden global i32
 ; COFF: @__llvm_profile_runtime = external hidden global i32
 
 ; ELF: $__profc_foo = comdat nodeduplicate
@@ -101,7 +101,7 @@ declare void @llvm.instrprof.increment(ptr, i64, i32, i32)
 ; ELF_GENERIC: @llvm.compiler.used = appending global [6 x ptr] [ptr @__llvm_profile_runtime, ptr @__profd_foo, ptr @__profd_foo_weak, ptr @"__profd_linkage.ll:foo_internal", ptr @__profd_foo_inline, ptr @__profd_foo_extern]
 ; MACHO:       @llvm.compiler.used = appending global [6 x ptr] [ptr @__llvm_profile_runtime_user, ptr @__profd_foo, {{.*}}
 ; COFF:        @llvm.compiler.used = appending global [6 x ptr] [ptr @__llvm_profile_runtime_user, ptr @__profd_foo, ptr @__profd_foo_weak, ptr @"__profd_linkage.ll:foo_internal", ptr @__profd_foo_inline, ptr @__profd_foo_extern]
-; XCOFF:       @llvm.used = appending global [7 x ptr] [ptr @__llvm_profile_runtime_user, ptr @__profd_foo, ptr @__profd_foo_weak, ptr @"__profd_linkage.ll:foo_internal", ptr @__profd_foo_inline, ptr @__profd_foo_extern, ptr @__llvm_prf_nm]
+; XCOFF:       @llvm.used = appending global [6 x ptr] [ptr @__profd_foo, ptr @__profd_foo_weak, ptr @"__profd_linkage.ll:foo_internal", ptr @__profd_foo_inline, ptr @__profd_foo_extern, ptr @__llvm_prf_nm]
 
 ; MACHO: define linkonce_odr hidden i32 @__llvm_profile_runtime_user() {{.*}} {
 ; MACHO:   %[[REG:.*]] = load i32, ptr @__llvm_profile_runtime
@@ -112,10 +112,7 @@ declare void @llvm.instrprof.increment(ptr, i64, i32, i32)
 ; ELFRT-NOT:   %[[REG:.*]] = load i32, ptr @__llvm_profile_runtime
 ; PS: define linkonce_odr hidden i32 @__llvm_profile_runtime_user() {{.*}} {
 ; PS:   %[[REG:.*]] = load i32, ptr @__llvm_profile_runtime
-; XCOFF: define linkonce_odr hidden i32 @__llvm_profile_runtime_user() {{.*}} {
-; XCOFF:   %[[REG:.*]] = load i32, ptr @__llvm_profile_runtime
-; XCOFF:   ret i32 %[[REG]]
-; XCOFF: }
+; XCOFF-NOT: define .* __llvm_profile_runtime_user
 
 ; ELF_GENERIC:      define internal void @__llvm_profile_register_functions() unnamed_addr {
 ; ELF_GENERIC-NEXT:   call void @__llvm_profile_register_function(ptr @__llvm_profile_runtime)