¶void computeKnownBits(
    const llvm::Value* V,
    const llvm::APInt& DemandedElts,
    llvm::KnownBits& Known,
    unsigned int Depth,
    const(anonymous namespace)::Query& Q)

Description

Determine which bits of V are known to be either zero or one and return them in the Known bit set. NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that we cannot optimize based on the assumption that it is zero without changing it to be an explicit zero. If we don't change it to zero, other code could optimized based on the contradictory assumption that it is non-zero. Because instcombine aggressively folds operations with undef args anyway, this won't lose us code quality. This function is defined on values with integer type, values with pointer type, and vectors of integers. In the case where V is a vector, known zero, and known one values are the same width as the vector element, and the bit is set only if it is true for all of the demanded elements in the vector specified by DemandedElts.

Declared at: llvm/lib/Analysis/ValueTracking.cpp:1913

Parameters

const llvm::Value* V

const llvm::APInt& DemandedElts

llvm::KnownBits& Known

unsigned int Depth

const(anonymous namespace)::Query& Q