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Commitbd1463e

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Error out for clang on x86-32 without SSE2 support, no -fexcess-precision.
As clang currently doesn't support -fexcess-precision=standard,compiling x86-32 code with SSE2 disabled, can lead to problems withfloating point overflow checks and the like.This issue was noticed because clang, on at least some BSDs, defaultsto i386 compatibility, whereas it defaults to pentium4 on Linux. Ourforced usage of __builtin_isinf() lead to some overflow checks nottriggering when compiling for i386, e.g. when the result of thecalculation didn't overflow in 80bit registers, but did so in 64bit.While we could just fall back to a non-builtin isinf, it seems likelythat the use of 80bit registers leads to other problems (which is whywe force the flag for GCC already). Therefore error out whendetecting clang in that situation.Reported-By: Victor WagnerAnalyzed-By: Andrew Gierth and Andres FreundAuthor: Andres FreundDiscussion:https://postgr.es/m/20180905005130.ewk4xcs5dgyzcy45@alap3.anarazel.deBackpatch: 9.3-, all supported versions are affected
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‎configure

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Original file line numberDiff line numberDiff line change
@@ -7023,6 +7023,39 @@ fi
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rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
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fi
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# Defend against clang being used on x86-32 without SSE2 enabled. As current
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# versions of clang do not understand -fexcess-precision=standard, the use of
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# x87 floating point operations leads to problems like isinf possibly returning
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# false for a value that is infinite when converted from the 80bit register to
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# the 8byte memory representation.
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#
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# Only perform the test if the compiler doesn't understand
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# -fexcess-precision=standard, that way a potentially fixed compiler will work
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# automatically.
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if test "$pgac_cv_prog_CC_cflags__fexcess_precision_standard" = no; then
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cat confdefs.h - <<_ACEOF >conftest.$ac_ext
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/* end confdefs.h. */
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int
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main ()
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{
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#if defined(__clang__) && defined(__i386__) && !defined(__SSE2_MATH__)
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choke me
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#endif
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;
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return 0;
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}
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_ACEOF
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if ac_fn_c_try_compile "$LINENO"; then :
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else
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as_fn_error $? "Compiling PostgreSQL with clang, on 32bit x86, requires SSE2 support. Use -msse2 or use gcc." "$LINENO" 5
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fi
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rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
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fi
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ac_ext=c
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ac_cpp='$CPP $CPPFLAGS'
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ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'

‎configure.in

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Original file line numberDiff line numberDiff line change
@@ -624,6 +624,24 @@ choke me
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@%:@endif])], [], [AC_MSG_ERROR([do not put -ffast-math in CFLAGS])])
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fi
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# Defend against clang being used on x86-32 without SSE2 enabled. As current
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# versions of clang do not understand -fexcess-precision=standard, the use of
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# x87 floating point operations leads to problems like isinf possibly returning
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# false for a value that is infinite when converted from the 80bit register to
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# the 8byte memory representation.
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#
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# Only perform the test if the compiler doesn't understand
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# -fexcess-precision=standard, that way a potentially fixed compiler will work
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# automatically.
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if test "$pgac_cv_prog_CC_cflags__fexcess_precision_standard" = no; then
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AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
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@%:@if defined(__clang__) && defined(__i386__) && !defined(__SSE2_MATH__)
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choke me
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@%:@endif
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])], [],
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[AC_MSG_ERROR([Compiling PostgreSQL with clang, on 32bit x86, requires SSE2 support. Use -msse2 or use gcc.])])
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fi
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AC_PROG_CPP
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AC_SUBST(GCC)
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