[BOLT] Skip the validation of CFG after it is finalized

When current state is `CFG_Finalized`, function `validateCFG()` should return true directly.

Reviewed By: maksfb, yota9, Kepontry

Differential Revision: https://reviews.llvm.org/D159410

bolt/lib/Core/BinaryFunction.cpp

@@ -3156,6 +3156,10 @@ void BinaryFunction::dumpGraphToFile(std::string Filename) const {
 }
 
 bool BinaryFunction::validateCFG() const {
+  // Skip the validation of CFG after it is finalized
+  if (CurrentState == State::CFG_Finalized)
+    return true;
+
   bool Valid = true;
   for (BinaryBasicBlock *BB : BasicBlocks)
     Valid &= BB->validateSuccessorInvariants();

bolt/test/verify-cfg.test

@@ -0,0 +1,8 @@
+# Verify if the `--verify-cfg` option might produce incorrect alerts.
+
+REQUIRES: system-linux
+
+RUN: %clang %cflags %p/Inputs/hello.c -o %t -Wl,-q
+RUN: llvm-bolt %t -o %t.bolt --verify-cfg 2>&1 | FileCheck %s
+
+CHECK-NOT: BOLT-ERROR: Invalid CFG detected after pass {{.*}}