[Rd] Build failure on powerpc64

[Martin Maechler]

>>>>> Tom Callaway 
>>>>>     on Thu, 12 Dec 2019 14:21:10 -0500 writes:

    > Hi R folks,

    > Went to build R 3.6.2 for Fedora/EPEL and got failures across the board.

    > Disabling the test suite for all non-intel architectures resolves most of
    > the failures, but powerpc64 dies in the compiler, specifically here:

    > gcc -m64  -I../../src/extra/xdr -I. -I../../src/include -I../../src/include
    > -I/usr/local/include -I../../src/nmath -DHAVE_CONFIG_H   -fopenmp -fPIC
    > -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
    > -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong
    > -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
    > -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mcpu=power8
    > -mtune=power8 -fasynchronous-unwind-tables -fstack-clash-protection  -c
    > arithmetic.c -o arithmetic.o
    > arithmetic.c:180:26: error: initializer element is not constant
    > 180 | static LDOUBLE q_1_eps = (1 / LDBL_EPSILON);
    > |                          ^
    > make[3]: *** [../../Makeconf:124: arithmetic.o] Error 1

    > Took me a bit to figure out why, but this is happening because on
    > powerpc64, gcc is compiled with -mlong-double-128, and the long double
    > format used on PPC is IBM's 128bit long double which is two doubles added
    > together. As a result, gcc can't safely do const assignments to long
    > doubles on ppc64, so it dies there.

    > The fix is easy enough, do not try to assign a value to a static long
    > double on ppc64.
    > --- ./src/main/arithmetic.c.orig        2019-12-12 18:30:12.416334062 +0000
    > +++ ./src/main/arithmetic.c     2019-12-12 18:30:44.966334062 +0000
    > @@ -179,7 +179,10 @@ void attribute_hidden InitArithmetic()
    > #endif
    > }

    > -#if HAVE_LONG_DOUBLE && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE)
    > +/* PowerPC 64 (when gcc has -mlong-double-128) breaks here because
    > + * of issues constant folding 128bit IBM long doubles.
    > + */
    > +#if HAVE_LONG_DOUBLE && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE) && !__PPC64__
    > static LDOUBLE q_1_eps = 1 / LDBL_EPSILON;
    > #else
    > static double  q_1_eps = 1 / DBL_EPSILON;


    > Hope that helps someone else.
    > Tom

Thank you, Tom.  That is "interesting"  ...

The piece in question had been added by me,
------------------------------------------------------------------------
r77193 | maechler | 2019-09-18 13:21:49 +0200 (Wed, 18 Sep 2019) | 1 line

 x %% +/- Inf  now typically return non-NaN; fix the "FIXME" in C
------------------------------------------------------------------------
in order to use double precision in order to deal with finite cases
close to Inf, etc.

IIUC, your proposed patch is really a workaround a bug on PPC64 ?

But note the check on LONG_DOUBLE is not the only one in R's
sources: Via 'grep' in src/main/*.?  I also see

connections.c 4285:#if HAVE_LONG_DOUBLE && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE)
connections.c 4329:#if HAVE_LONG_DOUBLE
connections.c 4379:#if HAVE_LONG_DOUBLE && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE)
connections.c 4514:#if HAVE_LONG_DOUBLE && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE)
connections.c 4592:#if HAVE_LONG_DOUBLE && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE)
format.c 250:#if defined(HAVE_LONG_DOUBLE) && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE)
format.c 285:#if defined(HAVE_LONG_DOUBLE) && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE)
format.c 339:#if defined(HAVE_LONG_DOUBLE) && (SIZEOF_LONG_DOUBLE > SIZEOF_DOUBLE)

Do they also need protection against this PPC64 bug ?

Best,

Martin Maechler
ETH Zurich and R Core Team