[InstrProf] No linkage prefixes in IRPGO names (#76994)

Change the format of IRPGO counter names to
`[<filepath>;]<mangled-name>` which is computed by
`GlobalValue::getGlobalIdentifier()` to fix #74565.

In fe051934cbb0aaf25d960d7d45305135635d650b
(https://reviews.llvm.org/D156569) the format of IRPGO counter names was
changed to be `[<filepath>;]<linkage-name>` where `<linkage-name>` is
basically `F.getName()` with some prefix, e.g., `_` or `l_` on Mach-O
(yes, it is confusing that `<linkage-name>` is computed with
`Mangler().getNameWithPrefix()` while `<mangled-name>` is just
`F.getName()`). We discovered in #74565 that this causes some missed
import issues on some targets and #74008 is a partial fix.

Since `<mangled-name>` may not match the `<linkage-name>` on some
targets like Mach-O, we will need to post-process the output of
`llvm-profdata order` before passing to the linker via `-order_file`.

Profiles generated after fe051934cbb0aaf25d960d7d45305135635d650b will
become stale after this diff, but I think this is acceptable since that
patch landed after the LLVM 18 cut which hasn't been released yet.

3 files changed, 15 insertions, 36 deletions

diff --git a/llvm/lib/ProfileData/InstrProf.cpp b/llvm/lib/ProfileData/InstrProf.cpp
index 134a400..4264da8 100644
--- a/llvm/lib/ProfileData/InstrProf.cpp
+++ b/llvm/lib/ProfileData/InstrProf.cpp
@@ -14,7 +14,6 @@
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -27,7 +26,6 @@
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/MDBuilder.h"
-#include "llvm/IR/Mangler.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
@@ -297,29 +295,20 @@ static StringRef getStrippedSourceFileName(const GlobalObject &GO) {
   return FileName;
 }
 
-// The PGO name has the format [<filepath>;]<linkage-name> where <filepath>; is
-// provided if linkage is local and <linkage-name> is the mangled function
-// name. The filepath is used to discriminate possibly identical function names.
-// ; is used because it is unlikely to be found in either <filepath> or
-// <linkage-name>.
+// The PGO name has the format [<filepath>;]<mangled-name> where <filepath>; is
+// provided if linkage is local and is used to discriminate possibly identical
+// mangled names. ";" is used because it is unlikely to be found in either
+// <filepath> or <mangled-name>.
 //
 // Older compilers used getPGOFuncName() which has the format
-// [<filepath>:]<function-name>. <filepath> is used to discriminate between
-// possibly identical function names when linkage is local and <function-name>
-// simply comes from F.getName(). This caused trouble for Objective-C functions
-// which commonly have :'s in their names. Also, since <function-name> is not
-// mangled, they cannot be passed to Mach-O linkers via -order_file. We still
-// need to compute this name to lookup functions from profiles built by older
-// compilers.
+// [<filepath>:]<mangled-name>. This caused trouble for Objective-C functions
+// which commonly have :'s in their names. We still need to compute this name to
+// lookup functions from profiles built by older compilers.
 static std::string
 getIRPGONameForGlobalObject(const GlobalObject &GO,
                             GlobalValue::LinkageTypes Linkage,
                             StringRef FileName) {
-  SmallString<64> Name;
-  // FIXME: Mangler's handling is kept outside of `getGlobalIdentifier` for now.
-  // For more details please check issue #74565.
-  Mangler().getNameWithPrefix(Name, &GO, /*CannotUsePrivateLabel=*/true);
-  return GlobalValue::getGlobalIdentifier(Name, Linkage, FileName);
+  return GlobalValue::getGlobalIdentifier(GO.getName(), Linkage, FileName);
 }
 
 static std::optional<std::string> lookupPGONameFromMetadata(MDNode *MD) {
diff --git a/llvm/tools/llvm-profdata/llvm-profdata.cpp b/llvm/tools/llvm-profdata/llvm-profdata.cpp
index 77197d3..05e96f48 100644
--- a/llvm/tools/llvm-profdata/llvm-profdata.cpp
+++ b/llvm/tools/llvm-profdata/llvm-profdata.cpp
@@ -3158,7 +3158,11 @@ static int order_main(int argc, const char *argv[]) {
   BalancedPartitioning BP(Config);
   BP.run(Nodes);
 
-  WithColor::note() << "# Ordered " << Nodes.size() << " functions\n";
+  OS << "# Ordered " << Nodes.size() << " functions\n";
+  OS << "# Warning: Mach-O may prefix symbols with \"_\" depending on the "
+        "linkage and this output does not take that into account. Some "
+        "post-processing may be required before passing to the linker via "
+        "-order_file.\n";
   for (auto &N : Nodes) {
     auto [Filename, ParsedFuncName] =
         getParsedIRPGOFuncName(Reader->getSymtab().getFuncOrVarName(N.Id));
diff --git a/llvm/unittests/ProfileData/InstrProfTest.cpp b/llvm/unittests/ProfileData/InstrProfTest.cpp
index 6a71a97..8ffb68d 100644
--- a/llvm/unittests/ProfileData/InstrProfTest.cpp
+++ b/llvm/unittests/ProfileData/InstrProfTest.cpp
@@ -542,22 +542,14 @@ TEST_F(InstrProfTest, test_memprof_merge) {
 TEST_F(InstrProfTest, test_irpgo_function_name) {
   LLVMContext Ctx;
   auto M = std::make_unique<Module>("MyModule.cpp", Ctx);
-  // Use Mach-O mangling so that non-private symbols get a `_` prefix.
-  M->setDataLayout(DataLayout("m:o"));
   auto *FTy = FunctionType::get(Type::getVoidTy(Ctx), /*isVarArg=*/false);
 
   std::vector<std::tuple<StringRef, Function::LinkageTypes, StringRef>> Data;
-  Data.emplace_back("ExternalFoo", Function::ExternalLinkage, "_ExternalFoo");
+  Data.emplace_back("ExternalFoo", Function::ExternalLinkage, "ExternalFoo");
   Data.emplace_back("InternalFoo", Function::InternalLinkage,
-                    "MyModule.cpp;_InternalFoo");
-  Data.emplace_back("PrivateFoo", Function::PrivateLinkage,
-                    "MyModule.cpp;l_PrivateFoo");
-  Data.emplace_back("WeakODRFoo", Function::WeakODRLinkage, "_WeakODRFoo");
-  // Test Objective-C symbols
+                    "MyModule.cpp;InternalFoo");
   Data.emplace_back("\01-[C dynamicFoo:]", Function::ExternalLinkage,
                     "-[C dynamicFoo:]");
-  Data.emplace_back("-<C directFoo:>", Function::ExternalLinkage,
-                    "_-<C directFoo:>");
   Data.emplace_back("\01-[C internalFoo:]", Function::InternalLinkage,
                     "MyModule.cpp;-[C internalFoo:]");
 
@@ -590,10 +582,6 @@ TEST_F(InstrProfTest, test_pgo_function_name) {
   Data.emplace_back("ExternalFoo", Function::ExternalLinkage, "ExternalFoo");
   Data.emplace_back("InternalFoo", Function::InternalLinkage,
                     "MyModule.cpp:InternalFoo");
-  Data.emplace_back("PrivateFoo", Function::PrivateLinkage,
-                    "MyModule.cpp:PrivateFoo");
-  Data.emplace_back("WeakODRFoo", Function::WeakODRLinkage, "WeakODRFoo");
-  // Test Objective-C symbols
   Data.emplace_back("\01-[C externalFoo:]", Function::ExternalLinkage,
                     "-[C externalFoo:]");
   Data.emplace_back("\01-[C internalFoo:]", Function::InternalLinkage,
@@ -611,8 +599,6 @@ TEST_F(InstrProfTest, test_pgo_function_name) {
 TEST_F(InstrProfTest, test_irpgo_read_deprecated_names) {
   LLVMContext Ctx;
   auto M = std::make_unique<Module>("MyModule.cpp", Ctx);
-  // Use Mach-O mangling so that non-private symbols get a `_` prefix.
-  M->setDataLayout(DataLayout("m:o"));
   auto *FTy = FunctionType::get(Type::getVoidTy(Ctx), /*isVarArg=*/false);
   auto *InternalFooF =
       Function::Create(FTy, Function::InternalLinkage, "InternalFoo", M.get());