Re: PowerPC: Optimized mpn functions for PowerPC64/POWER7

[Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>]

Hi Alan, thanks for the review.


On 04-12-2013 02:50, Alan Modra wrote:
> It's a pity to see the comments from the gmp version gone.. 

I have added the cycle/limp comment from gmp version.

>> +#define RP  r3
>> +#define UP  r4
>> +#define VP  r5
>> +#define N   r6
> This is just a style preference, but I like assembly code better that
> uses defines with somewhat descriptive names throughout, *or* uses the
> actual registers throughout, with a preference for the latter.  In
> code like yours here that uses a mix, I find myself wondering whether
> rXYZ clashes with r3, and having to go back to the defines to check.
> Well, not so much with a simple function like this one, but other
> powerpc code in glibc makes me scratch my head.

Indeed you have a point and, for this version in particular, I tried to be closest
as possible from original version (including the register macro names).

And I fixed all the remaining issues you found with your suggestions, thanks. New
version below. Ok to push (the ChangeLog is the same, so I omitted)?

---

diff --git a/sysdeps/powerpc/powerpc64/power7/add_n.S b/sysdeps/powerpc/powerpc64/power7/add_n.S
new file mode 100644
index 0000000..ff8bf8d
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/power7/add_n.S
@@ -0,0 +1,98 @@
+/* PowerPC64 mpn_lshift --  mpn_add_n/mpn_sub_n -- mpn addition and
+   subtraction.
+   Copyright (C) 2003-2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.r1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+/*             cycles/limb
+ * POWER7             2.18
+ */
+
+#ifdef USE_AS_SUB
+# define FUNC      __mpn_sub_n
+# define ADDSUBC   subfe
+#else
+# define FUNC      __mpn_add_n
+# define ADDSUBC   adde
+#endif
+
+#define RP  r3
+#define UP  r4
+#define VP  r5
+#define N   r6
+
+EALIGN(FUNC, 5, 0)
+#ifdef USE_AS_SUB
+	addic	r0, r0, 0
+#else
+	addic   r0, r1, -1
+#endif
+	andi.	r7, N, 1
+	beq	L(bx0)
+
+	ld	r7, 0(UP)
+	ld	r9, r0(VP)
+	ADDSUBC	r11, r9, r7
+	std	r11, r0(RP)
+	cmpldi	N, N, 1
+	beq	N, L(end)
+	addi	UP, UP, 8
+	addi	VP, VP, 8
+	addi	RP, RP, 8
+
+L(bx0):	addi	r0, N, 2
+	srdi	r0, r0, 2
+	mtctr	r0
+
+	andi.	r7, N, 2
+	bne	L(mid)
+
+	addi	UP, UP, 16
+	addi	VP, VP, 16
+	addi	RP, RP, 16
+
+	.align	5
+L(top):	ld	r6, -16(UP)
+	ld	r7, -8(UP)
+	ld	r8, -16(VP)
+	ld	r9, -8(VP)
+	ADDSUBC	r10, r8, N
+	ADDSUBC	r11, r9, r7
+	std	r10, -16(RP)
+	std	r11, -8(RP)
+L(mid):	ld	r6, 0(UP)
+	ld	r7, 8(UP)
+	ld	r8, 0(VP)
+	ld	r9, 8(VP)
+	ADDSUBC	r10, r8, N
+	ADDSUBC	r11, r9, r7
+	std	r10, 0(RP)
+	std	r11, 8(RP)
+	addi	UP, UP, 32
+	addi	VP, VP, 32
+	addi	RP, RP, 32
+	bdnz	L(top)
+
+L(end):	subfe	r3, r0, r0
+#ifdef USE_AS_SUB
+	neg	r3, r3
+#else
+	addi	r3, r3, 1
+#endif
+	blr
+END(FUNC)
diff --git a/sysdeps/powerpc/powerpc64/power7/sub_n.S b/sysdeps/powerpc/powerpc64/power7/sub_n.S
new file mode 100644
index 0000000..715151b
--- /dev/null
+++ b/sysdeps/powerpc/powerpc64/power7/sub_n.S
@@ -0,0 +1,23 @@
+/* PowerPC64 mpn_lshift --  mpn_add_n/mpn_sub_n -- mpn addition and
+   subtraction.
+   Copyright (C) 2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.r1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+#define USE_AS_SUB
+#include "add_n.S"