[LTO][lld] Add lto-pgo-warn-mismatch option

When enable CSPGO for ThinLTO, there are profile cfg mismatch warnings that will cause lld-link errors (with /WX)
due to source changes (e.g. `#if` code runs for profile generation but not for profile use)
To disable it we have to use an internal "/mllvm:-no-pgo-warn-mismatch" option.
In contrast clang uses option ”-Wno-backend-plugin“ to avoid such warnings and gcc has an explicit "-Wno-coverage-mismatch" option.

Add "lto-pgo-warn-mismatch" option to lld COFF/ELF to help turn on/off the profile mismatch warnings explicitly when build with ThinLTO and CSPGO.

Differential Revision: https://reviews.llvm.org/D104431

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index 5863ec6..6563af0 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -74,6 +74,10 @@ static cl::opt<bool> ThinLTOAssumeMerged(
     cl::desc("Assume the input has already undergone ThinLTO function "
              "importing and the other pre-optimization pipeline changes."));
 
+namespace llvm {
+extern cl::opt<bool> NoPGOWarnMismatch;
+}
+
 [[noreturn]] static void reportOpenError(StringRef Path, Twine Msg) {
   errs() << "failed to open " << Path << ": " << Msg << '\n';
   errs().flush();
@@ -221,6 +225,7 @@ static void runNewPMPasses(const Config &Conf, Module &Mod, TargetMachine *TM,
     PGOOpt = PGOOptions(Conf.CSIRProfile, "", Conf.ProfileRemapping,
                         PGOOptions::IRUse, PGOOptions::CSIRUse,
                         Conf.AddFSDiscriminator);
+    NoPGOWarnMismatch = !Conf.PGOWarnMismatch;
   } else if (Conf.AddFSDiscriminator) {
     PGOOpt = PGOOptions("", "", "", PGOOptions::NoAction,
                         PGOOptions::NoCSAction, true);