[PATCH] D115755: [InstSimplify] Fold logic And to Zero

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D115755#3204659 <https://reviews.llvm.org/D115755#3204659>, @spatel wrote:

> The code seems more complicated than necessary (and the tests less thorough than necessary). 
> We know that the 'or' instruction is a shared op, so let's match that first and then match it again as a specific value? 
> If I'm seeing it correctly, that means there are 8 potential commutes:
>
>   BinaryOperator *Or;
>   if (match(Op0, m_c_Xor(m_Value(X), m_BinOp(Or))))
>     if (match(Or, m_c_Or(m_Specific(X), m_Value(Y))) &&
>         match(Op1, m_c_Xor(m_Specific(Or), m_Specific(Y))))
>       return Constant::getNullValue(Op0->getType());

On 2nd thought, that might not be complicated enough. :)
I think this could match a "wrong" binop first (for example Y is an add instruction) and then fail to match the pattern (so we could use even more tests...).
We probably need to use `m_CombineAnd` to get this to accurately match Op0 and capture the 'or' in one shot:

  BinaryOperator *Or;
  if (match(Op0, m_c_Xor(m_Value(X),
                         m_CombineAnd(m_BinOp(Or),
                                      m_c_Or(m_Deferred(X), m_Value(Y))))) &&
      match(Op1, m_c_Xor(m_Specific(Or), m_Specific(Y))))
    return Constant::getNullValue(Op0->getType());


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115755/new/

https://reviews.llvm.org/D115755