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

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec added inline comments.


================
Comment at: llvm/lib/Analysis/InstructionSimplify.cpp:2180
+    return Constant::getNullValue(Op0->getType());
+  // ((A | B) ^ B ) & ((A | B) ^ A) --> 0
+  if (match(Op0, m_c_Xor(m_c_Or(m_Value(X), m_Value(Y)), m_Deferred(Y))) &&
----------------
MehrHeidar wrote:
> rampitec wrote:
> > MehrHeidar wrote:
> > > rampitec wrote:
> > > > You could use 'm_CombineOr' for the LHS to select either deferred X or deferred Y. Then you do not need second expression.
> > > I replaced the comments and changed the usage of A/B with X/Y.
> > > Also, I tried to use the idea for usage of `m_CombineOr` to remove the second expression.
> > Second match shall not use m_CombineOr. Now you would incorrectly match `((X | Y) ^ X ) & ((X | Y) ^ X)`. Speaking of which it deserves a negative test.
> If I don't put the `m_CombineOr` on the second match, we won't be able to catch all commutes. I added a negative test now to see it won't incorrectly match your example.
> 
> I am not so confident with the current code too and prefer my first version of this patch. What do you think @rampitec ?
> 
m_CombineOr is not about commute. At the point of second match you already know your X and Y exactly.


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

https://reviews.llvm.org/D115755