This is the mail archive of the 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: patch to fix constant math -5th patch, rtl

Richard Biener <> writes:
> I suppose the above should use immed_double_int_const (v, mode), too,

In practice it doesn't matter, because...

> which oddly only ever truncates to mode for modes <= HOST_BITS_PER_WIDE_INT
> via gen_int_mode.

...right.  That's because there's not really any proper support for
non-power-of-2 modes.  Partial modes like PDI are specified by things like:


which is glaringly absent of any bit width.  So if the constant is big
enough to need 2 HWIs, it in practice must be exactly 2 HWIs wide.
One of the advantages of wide_int is that it allows us to relax this
restriction: we can have both (a) mode widths greater than
HOST_BITS_PER_WIDE_INT*2 and (b) mode widths that are greater than
HOST_BITS_PER_WIDE_INT while not being a multiple of it.

In other words, one of the reasons wide_int can't be exactly 1:1
in practice is because it is clearing out these mistakes (GEN_INT
rather than gen_int_mode) and missing features (non-power-of-2 widths).


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