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Try to detect runtime unavailability of __builtin_mul_overflow(int64).

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On some systems the results of 64 bit __builtin_mul_overflow()
operations can be computed at compile time, but not at runtime. The
known cases are arm buildfar animals using clang where the runtime
operation is implemented in a unavailable function.

Try to avoid compile-time computation by using volatile arguments to
__builtin_mul_overflow(). In that case we hopefully will get a link
error when unavailable, similar to what buildfarm animals dangomushi
and gull are reporting.

Author: Andres Freund
Discussion: https://postgr.es/m/20171213213754.pydkyjs6bt2hvsdb@alap3.anarazel.de
This commit is contained in:
Andres Freund
2017-12-16 12:49:41 -08:00
parent c757a3da0a
commit c04d35f442
2 changed files with 11 additions and 5 deletions
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4
configure vendored
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@ -14488,8 +14488,10 @@ else
int
main ()
{
PG_INT64_TYPE a = 1;
PG_INT64_TYPE b = 1;
PG_INT64_TYPE result;
__builtin_mul_overflow((PG_INT64_TYPE) 1, (PG_INT64_TYPE) 2, &result);
__builtin_mul_overflow(*(volatile PG_INT64_TYPE *) a, *(volatile PG_INT64_TYPE *) b, &result);
;
return 0;