================
@@ -1520,15 +1520,72 @@ ConstantRange ConstantRange::binaryNot() const {
return ConstantRange(APInt::getAllOnes(getBitWidth())).sub(*this);
}
+/// Estimate the 'bit-masked AND' operation's lower bound.
+///
+/// E.g., given two ranges as follows (single quotes are separators and
+/// have no meaning here),
+///
+/// LHS = [10'00101'1, ; LLo
+/// 10'10000'0] ; LHi
+/// RHS = [10'11111'0, ; RLo
+/// 10'11111'1] ; RHi
+///
+/// we know that the higher 2 bits of the result is always 10; and we also
+/// notice that RHS[1:6] are always 1, so the result[1:6] cannot be less than
+/// LHS[1:6] (i.e., 00101). Thus, the lower bound is 10'00101'0.
+///
+/// The algorithm is as follows,
+/// 1. we first calculate a mask to find the higher common bits by
+/// Mask = ~((LLo ^ LHi) | (LLo ^ LHi) | (LLo ^ RLo));
----------------
MaskRay wrote:
`Mask = ~((LLo ^ LHi) | (RLo ^ RHi) | (LLo ^ RLo))`
https://github.com/llvm/llvm-project/pull/120352
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