[Bug target/114591] [12/13/14/15 Regression] register allocators introduce an extra load operation since gcc-12

[liuhongt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114591

--- Comment #18 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
(In reply to Hongtao Liu from comment #16)
> > 
> > 4952      /* See if a MEM has already been loaded with a widening operation;
> > 4953         if it has, we can use a subreg of that.  Many CISC machines
> > 4954         also have such operations, but this is only likely to be
> > 4955         beneficial on these machines.  */
> 
> Oh, it's pre_reload cse_insn, not postreload gcse

Current postreload gcse is supposed to handle inter-block redundant loads, but
for testcase in the PR, the redundancy it's inside the same block

------cut from postreload-gcse.cc -------------
 46/* The following code implements gcse after reload, the purpose of this
  47   pass is to cleanup redundant loads generated by reload and other
  48   optimizations that come after gcse. It searches for simple inter-block
  49   redundancies and tries to eliminate them by adding moves and loads
  50   in cold places.
------cut end ------------------------------