[BPI] Look through bitcasts in calcZeroHeuristic

[weiwang]

Summary

Constant hoisting may hide the constant value behind bitcast for And's
operand. Track down the constant to make the BFI result consistent
regardless of hoisting.

[samparker]

Thanks. It's okay to commit cleanup NFCs without review, so don't worry about these kind of patches up for review in the future.

[samparker]

But now I understand that this isn't an NFC! So can you add a test please?

[weiwang]

add test case

llvm/lib/Analysis/BranchProbabilityInfo.cpp

bool BranchProbabilityInfo::calcZeroHeuristics(const BasicBlock *BB,
   ConstantInt *CV = GetConstantInt(RHS);
   if (!CV)
     return false;
 
   // If the LHS is the result of AND'ing a value with a single bit bitmask,
   // we don't have information about probabilities.
   if (Instruction *LHS = dyn_cast<Instruction>(CI->getOperand(0)))
     if (LHS->getOpcode() == Instruction::And)
-      if (ConstantInt *AndRHS = dyn_cast<ConstantInt>(LHS->getOperand(1)))
+      if (ConstantInt *AndRHS = GetConstantInt(LHS->getOperand(1)))
         if (AndRHS->getValue().isPowerOf2())
           return false;
 
   // Check if the LHS is the return value of a library function
   LibFunc Func = NumLibFuncs;
   if (TLI)
     if (CallInst *Call = dyn_cast<CallInst>(CI->getOperand(0)))
       if (Function *CalledFn = Call->getCalledFunction())