From 2ffa8b8660a7a17572ae5a398171c8be59985eb3 Mon Sep 17 00:00:00 2001

From: "Gabriel F. T. Gomes" <gftg@linux.vnet.ibm.com>

Date: Mon, 25 Jan 2016 10:50:34 -0500

Subject: [PATCH] powerpc: Zero pad using memset in strncpy/stpncpy

Call __memset_power8 to pad, with zeros, the remaining bytes in the

dest string on __strncpy_power8 and __stpncpy_power8.  This improves

performance when n is larger than the input string, giving ~30% gain for

larger strings without impacting much shorter strings.

(cherry picked from commit 72c11b353ede72931cc474c9071d143d9a05c0d7)

---

 ChangeLog                                  |   5 ++

 sysdeps/powerpc/powerpc64/power8/strncpy.S | 123 +++++++++++++----------------

 2 files changed, 61 insertions(+), 67 deletions(-)

diff --git a/ChangeLog b/ChangeLog

index 5537fc6..8d0e296 100644

diff --git a/sysdeps/powerpc/powerpc64/power8/strncpy.S b/sysdeps/powerpc/powerpc64/power8/strncpy.S

index 5fda953..80136cc 100644

--- a/sysdeps/powerpc/powerpc64/power8/strncpy.S

+++ b/sysdeps/powerpc/powerpc64/power8/strncpy.S

@@ -24,6 +24,8 @@

 # define FUNC_NAME strncpy

 #endif

+#define FRAMESIZE (FRAME_MIN_SIZE+48)

+

 /* Implements the function

    char * [r3] strncpy (char *dest [r3], const char *src [r4], size_t n [r5])

@@ -54,8 +56,7 @@ EALIGN (FUNC_NAME, 4, 0)

 	addi	r10,r4,16

 	rlwinm	r9,r4,0,19,19

-	/* Since it is a leaf function, save some non-volatile registers on the

-	   protected/red zone.  */

+	/* Save some non-volatile registers on the stack.  */

 	std	r26,-48(r1)

 	std	r27,-40(r1)

@@ -69,6 +70,14 @@ EALIGN (FUNC_NAME, 4, 0)

 	std	r30,-16(r1)

 	std	r31,-8(r1)

+	/* Update CFI.  */

+	cfi_offset(r26, -48)

+	cfi_offset(r27, -40)

+	cfi_offset(r28, -32)

+	cfi_offset(r29, -24)

+	cfi_offset(r30, -16)

+	cfi_offset(r31, -8)

+

 	beq	cr7,L(unaligned_lt_16)

 	rldicl	r9,r4,0,61

 	subfic	r8,r9,8

@@ -144,74 +153,58 @@ L(short_path_loop_end):

 	ld	r31,-8(r1)

 	blr

-	/* This code pads the remainder dest with NULL bytes.  The algorithm

-	   calculate the remanining size and issues a doubleword unrolled

-	   loops followed by a byte a byte set.  */

+	/* This code pads the remainder of dest with NULL bytes.  The algorithm

+	   calculates the remaining size and calls memset.  */

 	.align	4

 L(zero_pad_start):

 	mr	r5,r10

 	mr	r9,r6

 L(zero_pad_start_1):

-	srdi.	r8,r5,r3

-	mr	r10,r9

-#ifdef USE_AS_STPNCPY

-	mr	r3,r9

+	/* At this point:

+	     - r5 holds the number of bytes that still have to be written to

+	       dest.

+	     - r9 points to the position, in dest, where the first null byte

+	       will be written.

+	   The above statements are true both when control reaches this label

+	   from a branch or when falling through the previous lines.  */

+#ifndef USE_AS_STPNCPY

+	mr	r30,r3       /* Save the return value of strncpy.  */

+#endif

+	/* Prepare the call to memset.  */

+	mr	r3,r9        /* Pointer to the area to be zero-filled.  */

+	li	r4,0         /* Byte to be written (zero).  */

+

+	/* We delayed the creation of the stack frame, as well as the saving of

+	   the link register, because only at this point, we are sure that

+	   doing so is actually needed.  */

+

+	/* Save the link register.  */

+	mflr	r0

+	std	r0,16(r1)

+	cfi_offset(lr, 16)

+

+	/* Create the stack frame.  */

+	stdu	r1,-FRAMESIZE(r1)

+	cfi_adjust_cfa_offset(FRAMESIZE)

+

+	bl	__memset_power8

+	nop

+

+	/* Restore the stack frame.  */

+	addi	r1,r1,FRAMESIZE

+	cfi_adjust_cfa_offset(-FRAMESIZE)

+	/* Restore the link register.  */

+	ld	r0,16(r1)

+	mtlr	r0

+

+#ifndef USE_AS_STPNCPY

+	mr	r3,r30       /* Restore the return value of strncpy, i.e.:

+				dest.  For stpncpy, the return value is the

+				same as return value of memset.  */

 #endif

-	beq-	cr0,L(zero_pad_loop_b_start)

-	cmpldi	cr7,r8,1

-	li	cr7,0

-	std	r7,0(r9)

-	beq	cr7,L(zero_pad_loop_b_prepare)

-	addic.	r8,r8,-2

-	addi	r10,r9,r16

-	std	r7,8(r9)

-	beq	cr0,L(zero_pad_loop_dw_2)

-	std	r7,16(r9)

-	li	r9,0

-	b	L(zero_pad_loop_dw_1)

-

-	.align	4

-L(zero_pad_loop_dw):

-	addi	r10,r10,16

-	std	r9,-8(r10)

-	beq	cr0,L(zero_pad_loop_dw_2)

-	std	r9,0(r10)

-L(zero_pad_loop_dw_1):

-	cmpldi	cr7,r8,1

-	std	r9,0(r10)

-	addic.	r8,r8,-2

-	bne	cr7,L(zero_pad_loop_dw)

-	addi	r10,r10,8

-L(zero_pad_loop_dw_2):

-	rldicl	r5,r5,0,61

-L(zero_pad_loop_b_start):

-	cmpdi	cr7,r5,0

-	addi	r5,r5,-1

-	addi	r9,r10,-1

-	add	r10,r10,5

-	subf	r10,r9,r10

-	li	r8,0

-	beq-	cr7,L(short_path_loop_end)

-

-	/* Write remaining 1-8 bytes.  */

-        .align  4

-	addi	r9,r9,1

-	mtocrf	0x1,r10

-	bf	29,4f

-        stw     r8,0(r9)

-        addi	r9,r9,4

-

-        .align  4

-4:      bf      30,2f

-        sth     r8,0(r9)

-        addi	r9,r9,2

-

-        .align  4

-2:      bf	31,1f

-        stb	r8,0(r9)

-	/* Restore non-volatile registers.  */

-1:	ld	r26,-48(r1)

+	/* Restore non-volatile registers and return.  */

+	ld	r26,-48(r1)

 	ld	r27,-40(r1)

 	ld	r28,-32(r1)

 	ld	r29,-24(r1)

@@ -407,10 +400,6 @@ L(short_path_prepare_2_3):

 	mr	r4,r28

 	mr	r9,r29

 	b	L(short_path_2)

-L(zero_pad_loop_b_prepare):

-	addi	r10,r9,8

-	rldicl	r5,r5,0,61

-	b	L(zero_pad_loop_b_start)

 L(zero_pad_start_prepare_1):

 	mr	r5,r6

 	mr	r9,r8

-- 

2.1.0