Re: [PATCH] Add _Float<N>/_Float<N>X rounding built-ins & improve gimple optimization of _Float<N>/_Float<N>X built-in functions

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

On Thu, Dec 21, 2017 at 01:03:26PM -0600, Segher Boessenkool wrote:
> On Thu, Dec 21, 2017 at 06:16:16PM +0000, Joseph Myers wrote:
> > On Fri, 17 Nov 2017, Michael Meissner wrote:
> > The architecture-independent changes are OK.  However, I have a comment on 
> > the target parts:
> > 
> > > +(define_insn "round<mode>2"
> > > +  [(set (match_operand:IEEE128 0 "altivec_register_operand" "=v")
> > > +	(unspec:IEEE128
> > > +	 [(match_operand:IEEE128 1 "altivec_register_operand" "v")]
> > > +	 UNSPEC_FRIN))]
> > > +  "TARGET_FLOAT128_HW && FLOAT128_IEEE_P (<MODE>mode)"
> > > +  "xsrqpi 0,%0,%1,3"
> > > +  [(set_attr "type" "vecfloat")
> > > +   (set_attr "size" "128")])
> > 
> > My reading of Power ISA 3.0B documentation is that 0,%0,%1,3 means round 
> > in the mode specified by FPSCR and you need 0,%0,%1,0 for 
> > round-to-nearest-away semantics which are what the round<mode>2 
> > instruction has (i.e., what you've written here is actually correct for 
> > nearbyint<mode>2, and would be rint<mode>2 if xsrqpix were used instead).  
> 
> Ah yes, the roundM2 insn is round-away-from-zero, so you are right.
> Tricky, from the name I assumed it would be "current rounding mode" :-/
> Not that "frin" would make sense if that were true.
> 
> Thanks!  And thanks for all the reviews in general.

Here is the corrected rs6000 part of the patch.  I added more round tests and I
checked it on a power9 prototype machine.  Roundf128 now produces the correct
answer.  Can I check this into the trunk?

[gcc]
2017-12-29  Michael Meissner  <meissner@linux.vnet.ibm.com>

	* config/rs6000/rs6000.md (floor<mode>2): Add support for IEEE
	128-bit round to integer instructions.
	(ceil<mode>2): Likewise.
	(btrunc<mode>2): Likewise.
	(round<mode>2): Likewise.

[gcc/testsuite]
2017-12-29  Michael Meissner  <meissner@linux.vnet.ibm.com>

	* gcc.target/powerpc/float128-hw2.c: Add tests for ceilf128,
	floorf128, truncf128, and roundf128.
	* gcc.target/powerpc/float128-hw5.c: New tests for _Float128
	optimizations added in match.pd.
	* gcc.target/powerpc/float128-hw6.c: Likewise.
	* gcc.target/powerpc/float128-hw7.c: Likewise.
	* gcc.target/powerpc/float128-hw8.c: Likewise.
	* gcc.target/powerpc/float128-hw9.c: Likewise.
	* gcc.target/powerpc/float128-hw10.c: Likewise.
	* gcc.target/powerpc/float128-hw11.c: Likewise.

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

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