The Alpha hardware predicts that forward conditional branches
    are not taken and that backwards conditional branches are taken.
    Based on the Alpha architecture, those assumptions are built into
    the compiler and influences the code generated for conditional
    branches.

    When .BRANCH_LIKELY precedes a forward conditional branch, the
    compiler will change the conditional branch and reorder the code
    such that the unlikely path will be a forward branch instead of
    the likely branch.

    The Itanium architecture includes branch prediction explicitly on
    each branch instruction. However, the compiler will still reorder
    the code to conform to the assumption that forward branches are
    not taken and backward branches are taken. The compiler will set
    the branch prediction flags as appropriate.