Re: PATCH: reorg branch displacement fix

[Jeff Law <law@porcupine.cygnus.com>]

In message <3DC2FC6F.D75062A5@superh.com>, Joern Rennecke writes:
 >> > * reorg.c (relax_delay_slots): Don't thread conditional jump
 >> > through unconditional jump if the conditional jump can't reach
 >> > the branch target on this processor target.
 >> This is wrong.  reorg does not and should not be checking branch displaceme
 >nts.
 >> That is a problem for shorten-branches and the backend.
 >
 >The SH does some early branch shortening in machine_dependent_reorg because
 >a long conditional branch has to be split into a short conditional branch
 >around an unconditional branch, or a short conditional branch to an unconditi
 >onal
 >branch (that might have been inserted elsewhere after an inverted condbranch)
 >.
 >Unconditional branches have mandatory delay slots, so we get additional
 >delay slots exposed by doing this splitting before reorg, and the conditional
 >branches have optional delay slots, which obviously can't be used in the same
 >way when the branch is reversed or redirected.
 >Thus, machine_dependent_reorg already makes sure all the conditional branches
 >that need splitting are split.  If reorg redirects conditional branches
 >willy-nilly, it destroys the very data it is supposed to operate on.
Regardless, reorg has never been designed to deal with this issue.  It can
lengthen the distance between branches in various ways other than simple
redirection.

This is _NOT_ reorg's problem to solve.  This is the backend's problem to
solve.

jeff