[PATCH 0/5] Fix handling of word subregs of wide registers

Jeff Law law@redhat.com
Fri Sep 19 06:14:00 GMT 2014


On 09/18/14 04:07, Richard Sandiford wrote:
> This series is a cleaned-up version of:
>
>      https://gcc.gnu.org/ml/gcc/2014-03/msg00163.html
>
> The underlying problem is that the semantics of subregs depend on the
> word size.  You can't have a subreg for byte 2 of a 4-byte word, say,
> but you can have a subreg for word 2 of a 4-word value (as well as lowpart
> subregs of that word, etc.).  This causes problems when an architecture has
> wider-than-word registers, since the addressability of a word can then depend
> on which register class is used.
>
> The register allocators need to fix up cases where a subreg turns out to
> be invalid for a particular class.  This is really an extension of what
> we need to do for CANNOT_CHANGE_MODE_CLASS.
>
> Tested on x86_64-linux-gnu, powerpc64-linux-gnu and aarch64_be-elf.
I thought we fixed these problems long ago with the change to subreg_byte?!?

Clearly I missed something.

jeff



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