Re: [PATCH] Avoid duplicate vector initializations during RTL expansion.

[Jeff Law <jeffreyalaw@gmail.com>]

On 6/11/23 10:15, Roger Sayle wrote:
> 
> This middle-end patch avoids some redundant RTL for vector initialization
> during RTL expansion.  For the simple test case:
> 
> typedef __int128 v1ti __attribute__ ((__vector_size__ (16)));
> __int128 key;
> 
> v1ti foo() {
>      return (v1ti){key};
> }
> 
> the middle-end currently expands:
> 
> (set (reg:V1TI 85) (const_vector:V1TI [ (const_int 0) ]))
> 
> (set (reg:V1TI 85) (mem/c:V1TI (symbol_ref:DI ("key"))))
> 
> where we create a dead instruction that initializes the vector to zero,
> immediately followed by a set of the entire vector.  This patch skips
> this zeroing instruction when the vector has only a single element.
> It also updates the code to indicate when we've cleared the vector,
> so that we don't need to initialize zero elements.
> 
> Interestingly, this code is very similar to my patch from April 2006:
> https://gcc.gnu.org/pipermail/gcc-patches/2006-April/192861.html
> 
> 
> This patch has been tested on x86_64-pc-linux-gnu with a make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}, with
> no new failures.  Ok for mainline?
> 
> 
> 2023-06-11  Roger Sayle  <roger@nextmovesoftware.com>
> 
> gcc/ChangeLog
>          * expr.cc (store_constructor) <case VECTOR_TYPE>: Don't bother
>          clearing vectors with only a single element.  Set CLEARED if the
>          vector was initialized to zero.
Funny how old (unresolved) issues will often raise their ugly heads again!

OK for the trunk.

jeff