Re: is Vax addressing sane today

EricP <ThatWouldBeTelling@thevillage.com> writes:

Kent Dickey wrote:

[...]

GCC's -trapv option is not useful for a variety of reasons.
1) its slow, about 50% performance hit
2) its always on for a compilation unit which is not what programmers need
   as it triggers for many false positives so people turn it off.

...

So why should any hardware include an instruction to trap-on-overflow?

>
Because ALL the negative speed and code size consequences do not occur.

Looking at <https://godbolt.org/z/oMhW55YsK> and selecting MIPS clang
18.1.0, I get a 15-instruction sequence which does not include add
(the trap-on-overflow version).

MIPS gcc 14.2.0 generates a sequence that includes

jal __addvsi3

i.e., just as for x86-64.  Similar for MIPS64 with these compilers.

Interestingly, with RISC-V rv64gc clang 18.1.0, the sequence is much
shorter than for MIPS clang 18.1.0, even though RV64GC has no specific
way of checking overflow at all.

- anton
--
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>