[Bug sim/27483] aarch64: adds test failing when adding 0x80000000 & 0xffffffff

[wilson at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=27483

--- Comment #5 from Jim Wilson <wilson at gcc dot gnu.org> ---
I realize that the 32-bit signed add has undefined result in the presence of
overflow.  But no matter what result you get, it can't match the result you get
for the 64-bit signed add when there is an overflow.  So the code should work. 
Unless maybe compiler optimization is doing something surprising which defeats
our code.

After some experimentation, I discovered that the code works with gcc-9 but
fails with gcc-10.  Because gcc-10 is doing some unexpected optimization of the
expression.

I can fix it by changing the code to
  if (sresult != (int32_t)sresult)
    flags |= V;
which should give the same result as before.  it works for me with gcc-10 on
the sim testsuite, though I haven't tried wider testing.

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