[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.

1 files changed, 5 insertions, 1 deletions

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));