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Commitc6d21d5

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Try harder to detect unavailability of __builtin_mul_overflow(int64).
Commitc04d35f didn't quite do the job here, because it still allowedthe compiler to deduce that the function call could be optimized away.Prevent that by putting the arguments and results in global variables.Discussion:https://postgr.es/m/20171213213754.pydkyjs6bt2hvsdb@alap3.anarazel.de
1 parentb31a9d7 commitc6d21d5

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2 files changed

+14
-12
lines changed

2 files changed

+14
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lines changed

‎config/c-compiler.m4

Lines changed: 9 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -310,18 +310,19 @@ fi])# PGAC_C_BUILTIN_CONSTANT_P
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# and define HAVE__BUILTIN_OP_OVERFLOW if so.
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#
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# Check for the most complicated case, 64 bit multiplication, as a
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# proxy for all of the operations.Use volatile variables to avoidthe
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#compiler computing result at compile time, even though the runtime
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#might not supply operation. Have to link to be sure to recognize a
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#missing __builtin_mul_overflow.
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# proxy for all of the operations. To detect the case wherethe compiler
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#knows the function but library support is missing, we must link not just
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#compile, and store the results in global variables so the compiler doesn't
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#optimize away the call.
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AC_DEFUN([PGAC_C_BUILTIN_OP_OVERFLOW],
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[AC_CACHE_CHECK(for__builtin_mul_overflow,pgac_cv__builtin_op_overflow,
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[AC_LINK_IFELSE([AC_LANG_PROGRAM([],
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[PG_INT64_TYPE a = 1;
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[AC_LINK_IFELSE([AC_LANG_PROGRAM([
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PG_INT64_TYPE a = 1;
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PG_INT64_TYPE b = 1;
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PG_INT64_TYPE result;
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__builtin_mul_overflow(*(volatile PG_INT64_TYPE *) a, *(volatile PG_INT64_TYPE *) b, &result);]
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)],
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int oflo;
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],
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[oflo = __builtin_mul_overflow(a, b, &result);])],
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[pgac_cv__builtin_op_overflow=yes],
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[pgac_cv__builtin_op_overflow=no])])
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if test x"$pgac_cv__builtin_op_overflow" = xyes ; then

‎configure

Lines changed: 5 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -14485,14 +14485,15 @@ else
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cat confdefs.h -<<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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14488-
int
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main ()
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{
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PG_INT64_TYPE a = 1;
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PG_INT64_TYPE b = 1;
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PG_INT64_TYPE result;
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__builtin_mul_overflow(*(volatile PG_INT64_TYPE *) a, *(volatile PG_INT64_TYPE *) b, &result);
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int oflo;
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14493+
int
14494+
main ()
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{
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oflo = __builtin_mul_overflow(a, b, &result);
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;
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return 0;
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}

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