[PATCH] D148986: [InstSimplify] with logical ops: (X | Y) ? 0 : X --> 0

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/lib/Analysis/InstructionSimplify.cpp:4597
+                                            Q, MaxRecurse))
+      return V;
   }
----------------
Not quite the code structure I had in mind. Rather than handling or in simplifySelectWithICmpEq, I'd expect something like this in here:

```
if (match(CmpLHS, m_Or(m_Value(X), m_Value(Y))) && match(CmpRHS, m_Zero())) {
  // X | Y == 0 implies X == 0 and Y == 0.
  if (Value *V = simplifySelectWithICmpEq(X, CmpRHS, TrueVal, FalseVal, Q,
                                          MaxRecurse))
      return V;
  if (Value *V = simplifySelectWithICmpEq(Y, CmpRHS, TrueVal, FalseVal, Q,
                                          MaxRecurse))
      return V;
}
```

That is, we handle the straightforward equality, and then we try to handle the implied equalities from the icmp or.


================
Comment at: llvm/test/Transforms/InstSimplify/select-cmp-or.ll:2
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=instsimplify,instcombine -S | FileCheck %s
+
----------------
Why does this also run instcombine?


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