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Re: [PR middle-end/20491] combine generates bad subregs
- From: Alexandre Oliva <aoliva at redhat dot com>
- To: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Cc: gcc-bugzilla at gcc dot gnu dot org, gcc-patches at gnu dot org
- Date: 25 Mar 2005 10:39:51 -0300
- Subject: Re: [PR middle-end/20491] combine generates bad subregs
- Organization: Red Hat Global Engineering Services Compiler Team
- References: <10503241239.AA13912@vlsi1.ultra.nyu.edu>
On Mar 24, 2005, kenner@vlsi1.ultra.nyu.edu (Richard Kenner) wrote:
> Combine doesn't ensure the subregs it generates are valid. In most
> cases, insn recog will reject the invalid subregs, or reload will
> some how make them fit, but if the constraint of the insn or the asm
> operand is "X", this won't work, so I think we're better off ensuring
> we don't ever introduce subregs of non-REGs.
> Aside from calling recog combine doesn't check that *anything* it generates
> is valid. Why should subregs be different?
Because, as I said, generating an invalid subreg at that point,
without any opportunity to fix it up later, will cause us to crash
when the time comes to remove all subregs.
--
Alexandre Oliva http://www.ic.unicamp.br/~oliva/
Red Hat Compiler Engineer aoliva@{redhat.com, gcc.gnu.org}
Free Software Evangelist oliva@{lsd.ic.unicamp.br, gnu.org}