On 06/06/2017 02:38 AM, Kyrill Tkachov wrote: > Hi all, > > Another vec_merge simplification that's missing from simplify-rtx.c is > transforming > a vec_merge of two vec_duplicates. For example: > (set (reg:V2DF 80) > (vec_merge:V2DF (vec_duplicate:V2DF (reg:DF 84)) > (vec_duplicate:V2DF (reg:DF 81)) > (const_int 2))) > > Can be transformed into the simpler: > (set (reg:V2DF 80) > (vec_concat:V2DF (reg:DF 81) > (reg:DF 84))) > > I believe this should always be beneficial. > I'm still looking into finding a small testcase demonstrating this, but > on aarch64 SPEC > I've seen this eliminate some really bizzare codegen where GCC was > generating nonsense like: > ldr q18, [sp, 448] > ins v18.d[0], v23.d[0] > ins v18.d[1], v22.d[0] > > With q18 being pushed and popped off the stack in the prologue and > epilogue of the function! > These are large files from SPEC that I haven't been able to analyse yet > as to why GCC even attempts > to do that, but with this patch it doesn't try to load a register and > overwrite all its lanes. > This patch shaves off about 5k of code size from zeusmp on aarch64 at > -O3, so I believe it's a good > thing to do. > > Ok? > > Thanks, > Kyrill > > 2017-06-06 Kyrylo Tkachov <kyrylo.tkac...@arm.com> > > * simplify-rtx.c (simplify_ternary_operation): Simplify vec_merge > of two vec_duplicates into a vec_concat. OK. Though I'd really like to see a testcase to exercise the simplification.
jeff
