[Bug target/95078] Missing fwprop for SIB address

["crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95078

--- Comment #2 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Richard Biener from comment #1)
> TER should go away, not be extended.  So you are suggesting that we replace
> 
>         leaq    44(%rdi,%rdx,4), %rdx  --- redundant could be fwprop
>         movl    (%rdx), %eax
>         movl    $3, (%rsi)
>         addl    (%rdx), %eax
> 
> with
> 
>         movl   44(%rdi,%rdx,4), %eax
>         movl    $3, (%rsi)
>         addl   44(%rdi,%rdx,4), %eax
> 
Yes.
> ?  The variant that looks bigger is actually one byte smaller.  Note as
> soon as there are three uses it will be larger again...
> 
> So this is really something for RTL and yeah, fwprop only makes "local"
> decisions.  Note that I think that your proposed variant will consume
> more resources since the complex addressing modes are likely split into
> a separate uop.  Yes, overall I'd expect less latency for your sequence.
Yes, also it will increase register pressure since propagation mostly would
increase live range for base and index reg, it's a subtle optimization, maybe 
a cost model could help, and fwprop should be more "smart" to see the
redundance of adress calculation after propagation.