[Bug target/70053] Returning a struct of _Decimal128 values generates extraneous stores and loads

[luoxhu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70053

--- Comment #9 from luoxhu at gcc dot gnu.org ---
(In reply to Segher Boessenkool from comment #8)
> I see no conversion there?
> 
> But, why does it it store to memory at all?

Yes, no conversion for this case, only adjust_address to TImode. mem/c:TD means
a MEM cannot trap.

Reason of store to memory:
D.2914 is a local struct variable here, seems we need do some optimization to
sink the D.2914.td0 and D.2914.td1 from BB3&BB4 to BB5 to avoid store/load on
stack? Or if there already exists some pass in Gimple? Or should this be
optimized after expander by some new pass like store sink?

O2/pr70053.c.234t.optimized:
D256_add_finite (_Decimal128 a, _Decimal128 b, _Decimal128 c)
{
  struct TDx2_t D.2914;

  <bb 2> [local count: 1073741824]:
  if (b_4(D) == c_5(D))
    goto <bb 3>; [34.00%]
  else
    goto <bb 4>; [66.00%]

  <bb 3> [local count: 365072224]:
  D.2914.td0 = c_5(D);
  D.2914.td1 = c_5(D);
  goto <bb 5>; [100.00%]

  <bb 4> [local count: 708669601]:
  D.2914.td0 = a_3(D);
  D.2914.td1 = b_4(D);

  <bb 5> [local count: 1073741824]:
  return D.2914;

}