isKnownToBeAPowerOfTwo: Strengthen isKnownToBeAPowerOfTwo's analysis on add instructions
Call into ComputeMaskedBits to figure out which bits are set on both add
operands and determine if the value is a power-of-two-or-zero or not.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187445 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 84a6346..4591af8 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -855,22 +855,36 @@
return false;
}
- if (match(V, m_Add(m_Value(X), m_Value(Y))))
- if (OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V))
- if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
- // Adding a power of two to the same power of two is a power of two or
- // zero.
- if (BinaryOperator *XBO = dyn_cast<BinaryOperator>(X))
- if (XBO->getOpcode() == Instruction::And)
- if (XBO->getOperand(0) == Y || XBO->getOperand(1) == Y)
- if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth))
- return true;
- if (BinaryOperator *YBO = dyn_cast<BinaryOperator>(Y))
- if (YBO->getOpcode() == Instruction::And)
- if (YBO->getOperand(0) == X || YBO->getOperand(1) == X)
- if (isKnownToBeAPowerOfTwo(X, OrZero, Depth))
- return true;
- }
+ // Adding a power-of-two or zero to the same power-of-two or zero yields
+ // either the original power-of-two, a larger power-of-two or zero.
+ if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
+ OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
+ if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
+ if (match(X, m_And(m_Specific(Y), m_Value())) ||
+ match(X, m_And(m_Value(), m_Specific(Y))))
+ if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth))
+ return true;
+ if (match(Y, m_And(m_Specific(X), m_Value())) ||
+ match(Y, m_And(m_Value(), m_Specific(X))))
+ if (isKnownToBeAPowerOfTwo(X, OrZero, Depth))
+ return true;
+
+ unsigned BitWidth = V->getType()->getScalarSizeInBits();
+ APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0);
+ ComputeMaskedBits(X, LHSZeroBits, LHSOneBits, 0, Depth);
+
+ APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0);
+ ComputeMaskedBits(Y, RHSZeroBits, RHSOneBits, 0, Depth);
+ // If i8 V is a power of two or zero:
+ // ZeroBits: 1 1 1 0 1 1 1 1
+ // ~ZeroBits: 0 0 0 1 0 0 0 0
+ if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2())
+ // If OrZero isn't set, we cannot give back a zero result.
+ // Make sure either the LHS or RHS has a bit set.
+ if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue())
+ 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