Issue with DI and SI mode

[Segher Boessenkool]

Hi!

On Tue, Jan 21, 2020 at 04:09:44PM +0100, Henri Cloetens wrote:
> long long int mem_read( long long int *a)
> {
> return(a[1000]) ;
> }
> 
> and the compiler (gcc 9.2.0) implements that as 2 32-bit reads.
> 
> The "movdi" is defined, the optimizers are turned on, and in the
> rtl dump, I see the "split2" step is splitting the "DI" in 2x "SI".
> 
> Any idea why this happens ?. Where should I look for this ?.

The split2 dump file will tell you what splitter was used (where it
was defined, what md file and line no, and what function in insn-emit.c
it ended up in).

A splitter is used if its pattern matches and its split condition is
true.  It isn't checked if the result is cheaper some way; it isn't
even checked if the resulting insns are valid at all.


Segher