libgfortran: Make sure glibc < 2.32 built powerpc64le-linux libgfortran doesn't use __*ieee128 APIs

I've just tried to build libgfortran on an old glibc system
(gcc112.fsffrance.org) and unfortunately we still have work to do:

[jakub@gcc2-power8 obj38]$ LD_PRELOAD=/home/jakub/gcc/obj38/powerpc64le-unknown-linux-gnu/libgfortran/.libs/libgfortran.so.5.0.0 /bin/true
[jakub@gcc2-power8 obj38]$ LD_BIND_NOW=1 LD_PRELOAD=/home/jakub/gcc/obj38/powerpc64le-unknown-linux-gnu/libgfortran/.libs/libgfortran.so.5.0.0 /bin/true
/bin/true: symbol lookup error: /home/jakub/gcc/obj38/powerpc64le-unknown-linux-gnu/libgfortran/.libs/libgfortran.so.5.0.0: undefined symbol: __atan2ieee128

While we do use some libquadmath APIs:
readelf -Wr /home/jakub/gcc/obj38/powerpc64le-unknown-linux-gnu/libgfortran/.libs/libgfortran.so.5.0.0 | grep QUADMATH
0000000000251268  000005e400000026 R_PPC64_ADDR64         0000000000000000 quadmath_snprintf@QUADMATH_1.0 + 0
0000000000251270  0000030600000026 R_PPC64_ADDR64         0000000000000000 strtoflt128@QUADMATH_1.0 + 0
00000000002502e0  0000011600000015 R_PPC64_JMP_SLOT       0000000000000000 ynq@QUADMATH_1.0 + 0
0000000000250390  0000016000000015 R_PPC64_JMP_SLOT       0000000000000000 sqrtq@QUADMATH_1.0 + 0
0000000000250508  000001fa00000015 R_PPC64_JMP_SLOT       0000000000000000 fmaq@QUADMATH_1.0 + 0
0000000000250530  0000021200000015 R_PPC64_JMP_SLOT       0000000000000000 fabsq@QUADMATH_1.0 + 0
0000000000250760  0000030600000015 R_PPC64_JMP_SLOT       0000000000000000 strtoflt128@QUADMATH_1.0 + 0
0000000000250990  000003df00000015 R_PPC64_JMP_SLOT       0000000000000000 cosq@QUADMATH_1.0 + 0
00000000002509f0  0000040a00000015 R_PPC64_JMP_SLOT       0000000000000000 expq@QUADMATH_1.0 + 0
0000000000250a88  0000045100000015 R_PPC64_JMP_SLOT       0000000000000000 erfcq@QUADMATH_1.0 + 0
0000000000250a98  0000045e00000015 R_PPC64_JMP_SLOT       0000000000000000 jnq@QUADMATH_1.0 + 0
0000000000250ac8  0000047e00000015 R_PPC64_JMP_SLOT       0000000000000000 sinq@QUADMATH_1.0 + 0
0000000000250e38  000005db00000015 R_PPC64_JMP_SLOT       0000000000000000 fmodq@QUADMATH_1.0 + 0
0000000000250e48  000005e000000015 R_PPC64_JMP_SLOT       0000000000000000 tanq@QUADMATH_1.0 + 0
0000000000250e58  000005e400000015 R_PPC64_JMP_SLOT       0000000000000000 quadmath_snprintf@QUADMATH_1.0 + 0
0000000000250f20  0000062900000015 R_PPC64_JMP_SLOT       0000000000000000 copysignq@QUADMATH_1.0 + 0
we don't do it consistently:
readelf -Wr /home/jakub/gcc/obj38/powerpc64le-unknown-linux-gnu/libgfortran/.libs/libgfortran.so.5.0.0 | grep ieee128
0000000000250310  0000012800000015 R_PPC64_JMP_SLOT       0000000000000000 __atan2ieee128 + 0
0000000000250340  0000014200000015 R_PPC64_JMP_SLOT       0000000000000000 __clogieee128 + 0
0000000000250438  000001a300000015 R_PPC64_JMP_SLOT       0000000000000000 __acoshieee128 + 0
00000000002504b8  000001cc00000015 R_PPC64_JMP_SLOT       0000000000000000 __csinieee128 + 0
0000000000250500  000001f300000015 R_PPC64_JMP_SLOT       0000000000000000 __sinhieee128 + 0
0000000000250570  0000022a00000015 R_PPC64_JMP_SLOT       0000000000000000 __asinieee128 + 0
0000000000250580  0000022d00000015 R_PPC64_JMP_SLOT       0000000000000000 __roundieee128 + 0
00000000002505a0  0000023e00000015 R_PPC64_JMP_SLOT       0000000000000000 __logieee128 + 0
00000000002505c8  0000024900000015 R_PPC64_JMP_SLOT       0000000000000000 __tanieee128 + 0
0000000000250630  0000027500000015 R_PPC64_JMP_SLOT       0000000000000000 __ccosieee128 + 0
0000000000250670  0000028a00000015 R_PPC64_JMP_SLOT       0000000000000000 __log10ieee128 + 0
00000000002506c8  000002bd00000015 R_PPC64_JMP_SLOT       0000000000000000 __cexpieee128 + 0
00000000002506d8  000002c800000015 R_PPC64_JMP_SLOT       0000000000000000 __coshieee128 + 0
00000000002509b0  000003ef00000015 R_PPC64_JMP_SLOT       0000000000000000 __truncieee128 + 0
0000000000250af8  000004a600000015 R_PPC64_JMP_SLOT       0000000000000000 __expieee128 + 0
0000000000250b50  000004c600000015 R_PPC64_JMP_SLOT       0000000000000000 __fmodieee128 + 0
0000000000250bb0  000004e700000015 R_PPC64_JMP_SLOT       0000000000000000 __tanhieee128 + 0
0000000000250c38  0000051300000015 R_PPC64_JMP_SLOT       0000000000000000 __acosieee128 + 0
0000000000250ce0  0000055400000015 R_PPC64_JMP_SLOT       0000000000000000 __sinieee128 + 0
0000000000250d60  0000057e00000015 R_PPC64_JMP_SLOT       0000000000000000 __atanieee128 + 0
0000000000250dd8  000005b100000015 R_PPC64_JMP_SLOT       0000000000000000 __sqrtieee128 + 0
0000000000250e98  0000060200000015 R_PPC64_JMP_SLOT       0000000000000000 __cosieee128 + 0
0000000000250eb0  0000060a00000015 R_PPC64_JMP_SLOT       0000000000000000 __atanhieee128 + 0
0000000000250ef0  0000062000000015 R_PPC64_JMP_SLOT       0000000000000000 __asinhieee128 + 0
0000000000250fd8  0000067f00000015 R_PPC64_JMP_SLOT       0000000000000000 __csqrtieee128 + 0
0000000000251038  000006ad00000015 R_PPC64_JMP_SLOT       0000000000000000 __cabsieee128 + 0
All these should for POWER_IEEE128 use atan2q@QUADMATH_1.0 etc.

It seems all these come from f951 compiled sources.
For user code, I think the agreement was if you want to use successfully
-mabi=ieeelongdouble, you need glibc 2.32 or later, which is why the Fortran
FE doesn't conditionalize on whether glibc 2.32 is available or not and just
emits __WHATEVERieee128 entrypoints.
But for Fortran compiled sources in libgfortran, we need to use
__WHATEVERieee128 only if glibc 2.32 or later and WHATEVERq (from
libquadmath) otherwise.

The following patch implements that, adds -fbuilding-libgfortran option
similar to e.g. -fbuilding-libgcc used when building libgcc and if
that option is set and the TARGET_GLIBC_{MAJOR,MINOR} macros indicate
no glibc or glibc older than 2.32, it will use the libquadmath APIs
rather than glibc 2.32 APIs.

2022-01-07  Jakub Jelinek  <jakub@redhat.com>

gcc/fortran/
	* trans-types.c (gfc_init_kinds): When setting abi_kind to 17, if not
	targetting glibc 2.32 or later and -fbuilding-libgfortran, set
	gfc_real16_is_float128 and c_float128 in gfc_real_kinds.
	(gfc_build_real_type): Don't set c_long_double if c_float128 is
	already set.
	* trans-intrinsic.c (builtin_decl_for_precision): Don't use
	long_double_built_in if gfc_real16_is_float128 and
	long_double_type_node == gfc_float128_type_node.
	* lang.opt (fbuilding-libgfortran): New undocumented option.
libgfortran/
	* Makefile.am (AM_FCFLAGS): Add -fbuilding-libgfortran after
	-fallow-leading-underscore.
	* Makefile.in: Regenerated.

5 files changed, 23 insertions, 9 deletions

diff --git a/gcc/fortran/lang.opt b/gcc/fortran/lang.opt
index 6db01c736be..7b63aa1bbd4 100644
--- a/gcc/fortran/lang.opt
+++ b/gcc/fortran/lang.opt
@@ -413,6 +413,9 @@ fblas-matmul-limit=
 Fortran RejectNegative Joined UInteger Var(flag_blas_matmul_limit) Init(30)
 -fblas-matmul-limit=<n>	Size of the smallest matrix for which matmul will use BLAS.
 
+fbuilding-libgfortran
+Fortran Undocumented Var(flag_building_libgfortran)
+
 fcheck-array-temporaries
 Fortran
 Produce a warning at runtime if a array temporary has been created for a procedure argument.
diff --git a/gcc/fortran/trans-intrinsic.c b/gcc/fortran/trans-intrinsic.c
index c928e577694..69d08ade1a9 100644
--- a/gcc/fortran/trans-intrinsic.c
+++ b/gcc/fortran/trans-intrinsic.c
@@ -154,7 +154,9 @@ builtin_decl_for_precision (enum built_in_function base_built_in,
     i = m->float_built_in;
   else if (precision == TYPE_PRECISION (double_type_node))
     i = m->double_built_in;
-  else if (precision == TYPE_PRECISION (long_double_type_node))
+  else if (precision == TYPE_PRECISION (long_double_type_node)
+	   && (!gfc_real16_is_float128
+	       || long_double_type_node != gfc_float128_type_node))
     i = m->long_double_built_in;
   else if (precision == TYPE_PRECISION (gfc_float128_type_node))
     {
diff --git a/gcc/fortran/trans-types.c b/gcc/fortran/trans-types.c
index 12b74207c99..5622725a4c8 100644
--- a/gcc/fortran/trans-types.c
+++ b/gcc/fortran/trans-types.c
@@ -516,7 +516,16 @@ gfc_init_kinds (void)
     {
       for (int i = 0; i < r_index; ++i)
 	if (gfc_real_kinds[i].kind == 16)
-	  gfc_real_kinds[i].abi_kind = 17;
+	  {
+	    gfc_real_kinds[i].abi_kind = 17;
+	    if (flag_building_libgfortran
+		&& (TARGET_GLIBC_MAJOR < 2
+		    || (TARGET_GLIBC_MAJOR == 2 && TARGET_GLIBC_MINOR < 32)))
+	      {
+		gfc_real16_is_float128 = true;
+		gfc_real_kinds[i].c_float128 = 1;
+	      }
+	  }
     }
 
   /* Choose the default integer kind.  We choose 4 unless the user directs us
@@ -859,7 +868,7 @@ gfc_build_real_type (gfc_real_info *info)
     info->c_float = 1;
   if (mode_precision == DOUBLE_TYPE_SIZE)
     info->c_double = 1;
-  if (mode_precision == LONG_DOUBLE_TYPE_SIZE)
+  if (mode_precision == LONG_DOUBLE_TYPE_SIZE && !info->c_float128)
     info->c_long_double = 1;
   if (mode_precision != LONG_DOUBLE_TYPE_SIZE && mode_precision == 128)
     {
diff --git a/libgfortran/Makefile.am b/libgfortran/Makefile.am
index fb83cbaae94..9c3514e5752 100644
--- a/libgfortran/Makefile.am
+++ b/libgfortran/Makefile.am
@@ -1079,8 +1079,8 @@ endif
 $(patsubst %.c,%.lo,$(notdir $(i_matmull_c))): AM_CFLAGS += -funroll-loops
 
 # Add the -fallow-leading-underscore option when needed
-$(patsubst %.F90,%.lo,$(patsubst %.f90,%.lo,$(notdir $(gfor_specific_src)))): AM_FCFLAGS += -fallow-leading-underscore
-selected_real_kind.lo selected_int_kind.lo: AM_FCFLAGS += -fallow-leading-underscore
+$(patsubst %.F90,%.lo,$(patsubst %.f90,%.lo,$(notdir $(gfor_specific_src)))): AM_FCFLAGS += -fallow-leading-underscore -fbuilding-libgfortran
+selected_real_kind.lo selected_int_kind.lo: AM_FCFLAGS += -fallow-leading-underscore -fbuilding-libgfortran
 
 # Build *_r17.F90 and *_c17.F90 with additional -mabi=ieeelongdouble on powerpc64le-linux.
 
@@ -1097,7 +1097,7 @@ endif
 
 if IEEE_SUPPORT
 # Add flags for IEEE modules
-$(patsubst %.F90,%.lo,$(notdir $(gfor_ieee_src))): AM_FCFLAGS += -Wno-unused-dummy-argument -Wno-c-binding-type -ffree-line-length-0 -fallow-leading-underscore
+$(patsubst %.F90,%.lo,$(notdir $(gfor_ieee_src))): AM_FCFLAGS += -Wno-unused-dummy-argument -Wno-c-binding-type -ffree-line-length-0 -fallow-leading-underscore -fbuilding-libgfortran
 endif
 
 # Dependencies between IEEE_ARITHMETIC and IEEE_EXCEPTIONS
diff --git a/libgfortran/Makefile.in b/libgfortran/Makefile.in
index ad5a10e0553..5de1b19ea0b 100644
--- a/libgfortran/Makefile.in
+++ b/libgfortran/Makefile.in
@@ -7633,8 +7633,8 @@ $(patsubst %.c,%.lo,$(notdir $(i_matmul_c))): AM_CFLAGS += -ffast-math -ftree-ve
 $(patsubst %.c,%.lo,$(notdir $(i_matmull_c))): AM_CFLAGS += -funroll-loops
 
 # Add the -fallow-leading-underscore option when needed
-$(patsubst %.F90,%.lo,$(patsubst %.f90,%.lo,$(notdir $(gfor_specific_src)))): AM_FCFLAGS += -fallow-leading-underscore
-selected_real_kind.lo selected_int_kind.lo: AM_FCFLAGS += -fallow-leading-underscore
+$(patsubst %.F90,%.lo,$(patsubst %.f90,%.lo,$(notdir $(gfor_specific_src)))): AM_FCFLAGS += -fallow-leading-underscore -fbuilding-libgfortran
+selected_real_kind.lo selected_int_kind.lo: AM_FCFLAGS += -fallow-leading-underscore -fbuilding-libgfortran
 
 # Build *_r17.F90 and *_c17.F90 with additional -mabi=ieeelongdouble on powerpc64le-linux.
 
@@ -7648,7 +7648,7 @@ selected_real_kind.lo selected_int_kind.lo: AM_FCFLAGS += -fallow-leading-unders
 @HAVE_REAL_17_TRUE@$(patsubst %_c17.c,%_c17.lo,$(notdir $(gfor_built_src))): AM_CFLAGS += -mabi=ieeelongdouble
 
 # Add flags for IEEE modules
-@IEEE_SUPPORT_TRUE@$(patsubst %.F90,%.lo,$(notdir $(gfor_ieee_src))): AM_FCFLAGS += -Wno-unused-dummy-argument -Wno-c-binding-type -ffree-line-length-0 -fallow-leading-underscore
+@IEEE_SUPPORT_TRUE@$(patsubst %.F90,%.lo,$(notdir $(gfor_ieee_src))): AM_FCFLAGS += -Wno-unused-dummy-argument -Wno-c-binding-type -ffree-line-length-0 -fallow-leading-underscore -fbuilding-libgfortran
 
 # Dependencies between IEEE_ARITHMETIC and IEEE_EXCEPTIONS
 ieee_arithmetic.lo: ieee/ieee_arithmetic.F90 ieee_exceptions.lo