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Re: How to clean up i386 machine description?
- To: hubicka at horac dot ta dot jcu dot cz (Jan Hubicka)
- Subject: Re: How to clean up i386 machine description?
- From: Joern Rennecke <amylaar at cygnus dot co dot uk>
- Date: Sat, 14 Nov 1998 06:44:49 +0000 (GMT)
- Cc: amylaar at cygnus dot co dot uk, howell at cs dot stanford dot edu, rth at cygnus dot com, law at cygnus dot com, pcg at goof dot com, egcs at cygnus dot com
> > There [might]
be a sequence that sets a register to one and then adds/subtracts
> > that value from another register. Reload might know about the equivalence
> > and decide to replace the register with the constant one in the add / subtract.
> > The instruction number is not recalculated in reload.
> Maybe stupid question, but why it should not be changed and recog the
> insn again?
During reload, one or more operands can be ill-formed. Only when reload
is finished can we be confident that the operands are all fixed up.
Hence, if we'd try to re-recognize an instruction during reload, this
would likely fail.