PHI nodes are not `FPMathOperator` s

[arsenm]

Test case?

[sanjoy]

In D58887#1416602, @arsenm wrote:

Test case?

I need this in a dependent change which has a test that fails without this fix. I can also add a C++ unit test in this change if you think that will help (I don't see an obvious way to test this using llvm-lit).

[arsenm]

I think unit tests are good for this sort of thing

[sanjoy]

Add unit test

[arsenm]

LGTM

[sanjoy]

Matt, I noticed a necessary change I had to make before landing this separately.
I didn't notice this because I was initially testing this combined with some
other changes.

include/llvm/IR/Operator.h

static bool classof(const Value *V) {
 
     switch (Opcode) {
     case Instruction::FCmp:
       return true;
     // non math FP Operators (no FMF)
     case Instruction::ExtractElement:
     case Instruction::ShuffleVector:
     case Instruction::InsertElement:
+    case Instruction::PHI:
       return false;
     default:
       return V->getType()->isFPOrFPVectorTy();
     }
   }
 };
 
 /// A helper template for defining operators for individual opcodes.