[gcc(refs/users/meissner/heads/work107)] Update ChangeLog.meissner

[Michael Meissner <meissner@gcc.gnu.org>]

https://gcc.gnu.org/g:16d92e2fddc2e80ba6634df75b11e68204cfd73e

commit 16d92e2fddc2e80ba6634df75b11e68204cfd73e
Author: Michael Meissner <meissner@linux.ibm.com>
Date:   Fri Jan 20 15:34:11 2023 -0500

    Update ChangeLog.meissner

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 gcc/ChangeLog.meissner | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/gcc/ChangeLog.meissner b/gcc/ChangeLog.meissner
index fda09a48c25..188ac07d434 100644
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+==================== work107, patch #1 ====================
+
+PR target/107299: Fix build issue when long double is IEEE 128-bit
+
+This patch updates the IEEE 128-bit types used in libgcc.
+
+At the moment, we cannot build GCC when the target uses IEEE 128-bit long
+doubles, such as building the compiler for a native Fedora 36 system.  The
+build dies when it is trying to build the _mulkc3.c and _divkc3 modules.
+
+This patch changes libgcc to use long double for the IEEE 128-bit base type if
+long double is IEEE 128-bit, and it uses _Float128 otherwise.  The built-in
+functions are adjusted to be the correct version based on the IEEE 128-bit base
+type used.
+
+While it is desirable to ultimately have __float128 and _Float128 use the same
+internal type and mode within GCC, at present if you use the option
+-mabi=ieeelongdouble, the __float128 type will use the long double type and not
+the _Float128 type.  We get an internal compiler error if we combine the
+signbitf128 built-in with a long double type.
+
+I've gone through several iterations of trying to fix this within GCC, and
+there are various problems that have come up.  I developed this alternative
+patch that changes libgcc so that it does not tickle the issue.  I hope we can
+fix the compiler at some point, but right now, this is preventing people on
+Fedora 36 systems from building compilers where the default long double is IEEE
+128-bit.
+
+I have built a GCC compiler tool chain on the following platforms and there
+were no regressions caused by these patches.
+
+    *	Power10 little endian, IBM long double, --with-cpu=power10
+
+    *	Power9 little endian, IBM long double, --with-cpu=power9
+
+    *	Power8 big endian, IBM long double, --with-cpu=power8, both
+	32-bit/64-bit tests.
+
+In addition, I have built a GCC compiler tool chain on the following systems
+with IEEE 128-bit long double as the default.  Comparing the test suite runs to
+the runs for the toolchain with IBM long double as the default, I only get the
+expected differences (C++ modules test fail on IEEE long double, 3 Fortran
+tests pass on IEEE long double that fail on IBM long double, C test pr105334.c
+fails, and C test fp128_conversions.c fails on power10):
+
+    *	Power10 little endian, IEEE long double, --with-cpu=power10
+
+    *	Power9 little endian, IEEE long double, --with-cpu=power9
+
+Can I check this change into the master branch?
+
+2023-01-20   Michael Meissner  <meissner@linux.ibm.com>
+
+	PR target/107299
+	* config/rs6000/_divkc3.c (COPYSIGN): Use the correct built-in based on
+	whether long double is IBM or IEEE.
+	(INFINITY): Likewise.
+	(FABS): Likewise.
+	* config/rs6000/_mulkc3.c (COPYSIGN): Likewise.
+	(INFINITY): Likewise.
+	* config/rs6000/quad-float128.h (TF): Remove definition.
+	(TFtype): Define to be long double or _Float128.
+	(TCtype): Define to be _Complex long double or _Complex _Float128.
+	* libgcc2.h (TFtype): Allow machine config files to override this.
+	(TCtype): Likewise.
+	* soft-fp/quad.h (TFtype): Likewise.
+
+==================== work107, branch head ====================
+
 2023-01-20   Michael Meissner  <meissner@linux.ibm.com>
 
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