[PR middle-end/20491] combine generates bad subregs

[Alexandre Oliva]

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}