[Bug middle-end/28831] [11/12/13/14/15 Regression] Aggregate copy not elided when using a return value as a pass-by-value parameter

[mkretz at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=28831

--- Comment #43 from Matthias Kretz (Vir) <mkretz at gcc dot gnu.org> ---
I see this issue in SIMD programming. Example (on x86_64 with only '-O2', i.e.
without AVX512) https://compiler-explorer.com/z/K64djP356:

typedef int V __attribute__((vector_size(64)));

V gen();

void g0(V const&, V const&);
void g1(V, V);

void constref()
{
  g0(gen(), gen());
}

void byvalue()
{
  g1(gen(), gen());
}

Both the 'constref' and 'byvalue' cases copy every V argument before calling
g0/g1.