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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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12
config/c-compiler.m4
View File

@ -310,13 +310,17 @@ fi])# PGAC_C_BUILTIN_CONSTANT_P
# and define HAVE__BUILTIN_OP_OVERFLOW if so.
#
# Check for the most complicated case, 64 bit multiplication, as a
# proxy for all of the operations. Have to link to be sure to
# recognize a missing __builtin_mul_overflow.
# proxy for all of the operations. Use volatile variables to avoid the
# compiler computing result at compile time, even though the runtime
# might not supply operation. Have to link to be sure to recognize a
# missing __builtin_mul_overflow.
AC_DEFUN([PGAC_C_BUILTIN_OP_OVERFLOW],
[AC_CACHE_CHECK(for __builtin_mul_overflow, pgac_cv__builtin_op_overflow,
[AC_LINK_IFELSE([AC_LANG_PROGRAM([],
[PG_INT64_TYPE result;
__builtin_mul_overflow((PG_INT64_TYPE) 1, (PG_INT64_TYPE) 2, &result);]
[PG_INT64_TYPE a = 1;
PG_INT64_TYPE b = 1;
PG_INT64_TYPE result;
__builtin_mul_overflow(*(volatile PG_INT64_TYPE *) a, *(volatile PG_INT64_TYPE *) b, &result);]
)],
[pgac_cv__builtin_op_overflow=yes],
[pgac_cv__builtin_op_overflow=no])])

4
configure vendored
View File

@ -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;