This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Make m32c build, fix PSImode truncation


On 04/27/2013 10:39 AM, Richard Sandiford wrote:
> Argh, that's unfortunate.  The point of that change was to make
> simplify_gen_unary (TRUNCATE, ...) no worse than using a subreg.
> Would the equivalent lowpart simplify_gen_subreg call succeed
> (return nonnull)?  If so, I think we want truncate to do the same.
> 
> What simplification is this blocking, and why does it lead to
> reload failures?

There's an explicit (set (reg:PSI) (truncate:PSI (reg:SI)) insn which
currently gets changed to (set (reg:PSI) (subreg:PSI (reg:SI)) during
cse1. Reload fails because the subreg gets propagated into a memory
address, which requires a class of A_REGS, but A_REGS can only hold
PSImode values, not SImode.  This shows that the truncation is not
always a no-op: in this case it involves a register move, but there's no
way to describe this using TRULY_NOOP_TRUNCATION.


Bernd


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]