Re: [PATCH], Backport IEEE 128-bit changes to GCC 8.x, preliminary, Patch #3

[Michael Meissner <meissner at linux dot ibm dot com>]

As we have discussed on the patch submission, I'm going to be back porting the
IEEE 128-bit changes that we've made recently in the trunk to the GCC 8.x
branch.  The motivation is to allow distributions to switch to IEEE 128-bit
long double without having to wait for the GCC 9.1 compiler.

I'm sending out these patches in terms of the submission to the FSF trunk.  I
will probably wait a few days before committing the patches just in case
something major was broken.

Patch #1 is the May 21st submission.  Note, in this patch, we had 3 separate
types activelly used (__ibm128, __float128, and long double).  However we
eventually decided we only wanted to use 2 types, and this changed in Patch #2.

Patch #2 is the June 1-8th changes by me (Michael Meissner), Segher Boessenkool
and David Edelsohn.  In the second set of changed we changed this to the
current two active types, one of which is the long double type, and other is
the alternate type.  We also changed the C++ mangling of the float128 type (and
long double if it uses the IEEE 128-bit encoding) from "U10__float128" to
"u9__ieee128".  We put out weak aliases so that old code could still call
functions compiled with the new compiler.

Patch #3 is the change committed on June 18th that reworks the internal
ordering of the 128-bit binary floating point types.  This prevents the machine
independent portions of the compiler trying to convert __ibm128 data to
__float128 if you are running on a Power9 (ISA 3.0) system that has 128-bit
hardware floating point support.

Patch #4 will be a collection of small patches to fix some problems that were
noticed in running the test suite with the long double default changed to IEEE
128-bit floating point.

This is patch #3.

[gcc]
2018-06-18  Michael Meissner  <meissner@linux.ibm.com>

	Back port from trunk
	2018-06-18  Michael Meissner  <meissner@linux.ibm.com>

	PR target/85358
	* config/rs6000/rs6000-modes.def (toplevel): Rework the 128-bit
	floating point modes, so that IFmode is numerically greater than
	TFmode, which is greater than KFmode using FRACTIONAL_FLOAT_MODE
	to declare the ordering.  This prevents IFmode from being
	converted to TFmode when long double is IEEE 128-bit on an ISA 3.0
	machine.  Include rs6000-modes.h to share the fractional values
	between genmodes* and the rest of the compiler.
	(IFmode): Likewise.
	(KFmode): Likewise.
	(TFmode): Likewise.
	* config/rs6000/rs6000-modes.h: New file.
	* config/rs6000/rs6000.c (rs6000_debug_reg_global): Change the
	meaning of rs6000_long_double_size so that 126..128 selects an
	appropriate 128-bit floating point type.
	(rs6000_option_override_internal): Likewise.
	* config/rs6000/rs6000.h (toplevel): Include rs6000-modes.h.
	(TARGET_LONG_DOUBLE_128): Change the meaning of
	rs6000_long_double_size so that 126..128 selects an appropriate
	128-bit floating point type.
	(LONG_DOUBLE_TYPE_SIZE): Update comment.
	* config/rs6000/rs6000.md (trunciftf2): Correct the modes of the
	source and destination to match the standard usage.
	(truncifkf2): Likewise.
	(copysign<mode>3, IEEE iterator): Rework copysign of float128 on
	ISA 2.07 to use an explicit clobber, instead of passing in a
	temporary.
	(copysign<mode>3_soft): Likewise.

[libgcc]
2018-06-18  Michael Meissner  <meissner@linux.ibm.com>

	Back port from trunk
	2018-06-18  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/t-float128 (FP128_CFLAGS_SW): Compile float128
	support modules with -mno-gnu-attribute.
	* config/rs6000/t-float128-hw (FP128_CFLAGS_HW): Likewise.

-- 
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meissner@linux.ibm.com, phone: +1 (978) 899-4797

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