[llvm] [InstCombine] Improve `(icmp pred (and X, Y), ...)` fold. (PR #66787)

[Nikita Popov via llvm-commits]

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@@ -233,56 +233,116 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner {
                                                 PatternMatch::m_Value()));
   }
 
-  /// Return true if the specified value is free to invert (apply ~ to).
-  /// This happens in cases where the ~ can be eliminated.  If WillInvertAllUses
-  /// is true, work under the assumption that the caller intends to remove all
-  /// uses of V and only keep uses of ~V.
-  ///
-  /// See also: canFreelyInvertAllUsersOf()
-  static bool isFreeToInvert(Value *V, bool WillInvertAllUses,
-                             unsigned Depth = 0) {
+  /// Return nonnull value if V is free to invert (with condition) regarding
+  /// WillInvertAllUses.
+  /// If Builder is nonnull, it will return a simplified ~V
+  /// If builder is null, it will return an arbitrary nonnull value (not
+  /// dereferenceable).
+  static Value *getFreeInverted(Value *V, bool WillInvertAllUses,
+                                BuilderTy *Builder, unsigned Depth = 0) {
+    static Value *const kNonNull = reinterpret_cast<Value *>(uintptr_t(1));
     // ~(~(X)) -> X.
-    if (match(V, m_Not(PatternMatch::m_Value())))
-      return true;
+    Value *A, *B;
+    if (match(V, m_Not(PatternMatch::m_Value(A))))
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nikic wrote:

As you're touching all the code in here anyway, I'd add a `using namespace llvm::PatternMatch` inside this function, so make the implementation more idiomatic...

https://github.com/llvm/llvm-project/pull/66787