[InstCombine] Simplify 'add' to 'or' if no common bits are set.

Summary:
In order to get the whole fold as specified in [[ https://bugs.llvm.org/show_bug.cgi?id=6773 | PR6773 ]],
let's first handle the simple straight-forward things.
Let's start with the `and` -> `or` simplification.

The one obvious thing missing here: the constant mask is not handled.
I have an idea how to handle it, but it will require some thinking,
and is not strictly required here, so i've left that for later.

https://rise4fun.com/Alive/Pkmg

Reviewers: spatel, craig.topper, eli.friedman, jingyue

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D45631

llvm-svn: 330101

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 1a41d0c..ac29cde0 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -190,6 +190,14 @@ bool llvm::haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
          "LHS and RHS should have the same type");
   assert(LHS->getType()->isIntOrIntVectorTy() &&
          "LHS and RHS should be integers");
+  // Look for an inverted mask: (X & ~M) op (Y & M).
+  Value *M;
+  if (match(LHS, m_c_And(m_Not(m_Value(M)), m_Value())) &&
+      match(RHS, m_c_And(m_Specific(M), m_Value())))
+    return true;
+  if (match(RHS, m_c_And(m_Not(m_Value(M)), m_Value())) &&
+      match(LHS, m_c_And(m_Specific(M), m_Value())))
+    return true;
   IntegerType *IT = cast<IntegerType>(LHS->getType()->getScalarType());
   KnownBits LHSKnown(IT->getBitWidth());
   KnownBits RHSKnown(IT->getBitWidth());