[llvm] [CodeGen] Preserve branch weights from PGO profile during instruction selection at -O0 (PR #161620)

[via llvm-commits]

================
@@ -229,6 +229,19 @@ static bool dontUseFastISelFor(const Function &Fn) {
   });
 }
 
+static bool shouldRegisterPGOPasses(const TargetMachine &TM,
----------------
WenleiHe wrote:

nit on naming, use something like `maintainPGOProfile` instead as PGO passes are a lot more than just BPI/BFI. 

https://github.com/llvm/llvm-project/pull/161620