Description

   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.