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Commit9220b00

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Tighten configure's test for __builtin_constant_p().
Commit9fa6f00 assumed that __builtin_constant_p("string literal")is TRUE, if the compiler has that function at all. Buildfarm resultsshow that Sun Studio 12, at least, breaks that assumption. Removingthat usage would leave us with no mechanical check for a very fragilecoding requirement, so instead teach configure to ignore__builtin_constant_p() if it doesn't behave that way. We couldcomplicate matters by distinguishing three cases (no such function,vs does, vs doesn't work for string literals); but for now, that seemsunnecessary because our other existing uses of this function are justfairly minor optimizations of non-returning elog/ereport. We can livewithout that on the small population of compilers that act this way.Discussion:https://postgr.es/m/22997.1513264066@sss.pgh.pa.us
1 parent11b8f07 commit9220b00

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‎config/c-compiler.m4

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@@ -285,10 +285,15 @@ fi])# PGAC_C_BUILTIN_BSWAP64
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# -------------------------
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# Check if the C compiler understands __builtin_constant_p(),
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# and define HAVE__BUILTIN_CONSTANT_P if so.
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# We need __builtin_constant_p("string literal") to be true, but some older
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# compilers don't think that, so test for that case explicitly.
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AC_DEFUN([PGAC_C_BUILTIN_CONSTANT_P],
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[AC_CACHE_CHECK(for__builtin_constant_p,pgac_cv__builtin_constant_p,
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[AC_COMPILE_IFELSE([AC_LANG_SOURCE(
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[[static int x; static int y[__builtin_constant_p(x) ? x : 1];]]
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[[static int x;
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static int y[__builtin_constant_p(x) ? x : 1];
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static int z[__builtin_constant_p("string literal") ? 1 : x];
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]]
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)],
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[pgac_cv__builtin_constant_p=yes],
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[pgac_cv__builtin_constant_p=no])])

‎configure

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Original file line numberDiff line numberDiff line change
@@ -11901,7 +11901,10 @@ if ${pgac_cv__builtin_constant_p+:} false; then :
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else
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cat confdefs.h -<<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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static int x; static int y[__builtin_constant_p(x) ? x : 1];
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static int x;
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static int y[__builtin_constant_p(x) ? x : 1];
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static int z[__builtin_constant_p("string literal") ? 1 : x];
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_ACEOF
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if ac_fn_c_try_compile"$LINENO";then:

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