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Re: [patch] inc/dec improvement on H8/300 and H8/S (revised)
- To: Kazu Hirata <kazu at hxi dot com>
- Subject: Re: [patch] inc/dec improvement on H8/300 and H8/S (revised)
- From: Jeffrey A Law <law at cygnus dot com>
- Date: Thu, 20 Jul 2000 17:42:01 -0600
- cc: gcc-patches at gcc dot gnu dot org
- Reply-To: law at cygnus dot com
In message <41ECF07CC183D111A6F800805FEDAB190CE691@EXCHANGE1>you write:
> Actually, I have thought about that. I found the following in gcc's manual
> under "Machine Descriptions/Defining Jump Instruction Patterns", but I don'
> t
> know what they mean by "until the end." The end of compilation? Until the
> peephole?
>
> "The reason you can do this is that GNU CC always generates a pair of
> consecutive RTL insns, possibly separated by note insns, one to set the
> condition code and one to test it, and keeps the pair inviolate until the
> end."
They stay together until redundant tst elimination which happens before
final assembly output and is responsible for using the result of a previous
insn which changes the condition codes to delete a redundant tst instruction.
jeff