isKnownToBeAPowerOfTwo: (X & Y) + Y is a power of 2 or zero if y is also.
This is useful if something that looks like (x & (1 << y)) ? 64 : 32 is
the divisor in a modulo operation.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182200 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 45dcc5e3..ca84a0c 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -855,6 +855,17 @@
return false;
}
+ // Adding a power of two to the same power of two is a power of two or zero.
+ if (OrZero && match(V, m_Add(m_Value(X), m_Value(Y)))) {
+ if (match(X, m_And(m_Value(), m_Specific(Y)))) {
+ if (isKnownToBeAPowerOfTwo(Y, /*OrZero*/true, Depth))
+ return true;
+ } else if (match(Y, m_And(m_Value(), m_Specific(X)))) {
+ if (isKnownToBeAPowerOfTwo(X, /*OrZero*/true, Depth))
+ return true;
+ }
+ }
+
// An exact divide or right shift can only shift off zero bits, so the result
// is a power of two only if the first operand is a power of two and not
// copying a sign bit (sdiv int_min, 2).