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Re: PATCH: reorg branch displacement fix

On Fri, 1 Nov 2002, Joern Rennecke wrote:

> > > * 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 displacements.
> > 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 unconditional
> 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.

It sounds like there should be a machine-independent branch-lengthening
pass for machines which have limited branch displacements. There must be
other processors which have this same problem?


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