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Let fpclassify use the builtin when optimizing for size in C++ mode (bug 22146)

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When optimization for size is on (-Os), fpclassify does not use the
type-generic __builtin_fpclassify builtin, instead it uses __MATH_TG.
However, when library support for float128 is available, __MATH_TG uses
__builtin_types_compatible_p, which is not available in C++ mode.

On the other hand, libstdc++ undefines (in cmath) many macros from
math.h, including fpclassify, so that it can provide its own functions.
However, during its configure tests, libstdc++ just tests for the
availability of the macros (it does not undefine them, nor does it
provide its own functions).

Finally, when libstdc++ is configured with optimization for size
enabled, its configure tests include math.h and get the definition of
fpclassify that uses __MATH_TG (and __builtin_types_compatible_p).
Since libstdc++ does not undefine the macros during its configure tests,
they fail.

This patch lets fpclassify use the builtin in C++ mode, even when
optimization for size is on.  This allows the configure test in
libstdc++ to work.

Tested for powerpc64le and x86_64.

	[BZ #22146]
	math/math.h: Let fpclassify use the builtin in C++ mode, even
	when optimazing for size.

(cherry picked from commit c5c4a62609)
This commit is contained in:
Gabriel F. T. Gomes 2017-09-20 15:10:26 -03:00
parent 37d4262a7a
commit d37c951fde
3 changed files with 14 additions and 1 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2017-09-22 Gabriel F. T. Gomes <gabriel@inconstante.eti.br>
[BZ #22146]
math/math.h: Let fpclassify use the builtin in C++ mode, even
when optimazing for size.
2017-08-22 Gabriel F. T. Gomes <gftg@linux.vnet.ibm.com>
* include/libc-symbols.h: [!defined HAVE_GCC_IFUNC] (__ifunc):

1
NEWS
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@ -30,6 +30,7 @@ The following bugs are resolved with this release:
[21972] assert macro requires operator== (int) for its argument type
[22095] resolv: Fix memory leak with OOM during resolv.conf parsing
[22096] resolv: __resolv_conf_attach must not free passed conf object
[22146] Let fpclassify use the builtin when optimizing for size in C++ mode
Version 2.26

8
math/math.h
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@ -402,7 +402,13 @@ enum
/* Return number of classification appropriate for X. */
# if __GNUC_PREREQ (4,4) && !defined __SUPPORT_SNAN__ \
&& !defined __OPTIMIZE_SIZE__
&& (!defined __OPTIMIZE_SIZE__ || defined __cplusplus)
/* The check for __cplusplus allows the use of the builtin, even
when optimization for size is on. This is provided for
libstdc++, only to let its configure test work when it is built
with -Os. No further use of this definition of fpclassify is
expected in C++ mode, since libstdc++ provides its own version
of fpclassify in cmath (which undefines fpclassify). */
# define fpclassify(x) __builtin_fpclassify (FP_NAN, FP_INFINITE, \
FP_NORMAL, FP_SUBNORMAL, FP_ZERO, x)
# else