[Bug middle-end/20491] [4.0/4.1 Regression] internal compiler error: in subreg_regno_offset, at rtlanal.c:3042

[aoliva at redhat dot com]

------- Additional Comments From aoliva at gcc dot gnu dot org  2005-03-25 13:41 -------
Subject: Re: [PR middle-end/20491] combine generates bad subregs

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.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20491