ARM: 8745/1: get rid of __memzero()

The __memzero assembly code is almost identical to memset's except for
two orr instructions. The runtime performance of __memset(p, n) and
memset(p, 0, n) is accordingly almost identical.

However, the memset() macro used to guard against a zero length and to
call __memzero at compile time when the fill value is a constant zero
interferes with compiler optimizations.

Arnd found tha the test against a zero length brings up some new
warnings with gcc v8:

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82103

And successively rremoving the test against a zero length and the call
to __memzero optimization produces the following kernel sizes for
defconfig with gcc 6:

    text     data     bss       dec       hex  filename
12248142  6278960  413588  18940690   1210312  vmlinux.orig
12244474  6278960  413588  18937022   120f4be  vmlinux.no_zero_test
12239160  6278960  413588  18931708   120dffc  vmlinux.no_memzero

So it is probably not worth keeping __memzero around given that the
compiler can do a better job at inlining trivial memset(p,0,n) on its
own. And the memset code already handles a zero length just fine.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

2 files changed, 1 insertions, 138 deletions

diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 4cb0b9624d8f..ad25fd1872c7 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -8,7 +8,7 @@
 lib-y		:= backtrace.o changebit.o csumipv6.o csumpartial.o   \
 		   csumpartialcopy.o csumpartialcopyuser.o clearbit.o \
 		   delay.o delay-loop.o findbit.o memchr.o memcpy.o   \
-		   memmove.o memset.o memzero.o setbit.o              \
+		   memmove.o memset.o setbit.o                        \
 		   strchr.o strrchr.o                                 \
 		   testchangebit.o testclearbit.o testsetbit.o        \
 		   ashldi3.o ashrdi3.o lshrdi3.o muldi3.o             \
diff --git a/arch/arm/lib/memzero.S b/arch/arm/lib/memzero.S
deleted file mode 100644
index 0eded952e089..000000000000
--- a/arch/arm/lib/memzero.S
+++ /dev/null
@@ -1,137 +0,0 @@
-/*
- *  linux/arch/arm/lib/memzero.S
- *
- *  Copyright (C) 1995-2000 Russell King
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- */
-#include <linux/linkage.h>
-#include <asm/assembler.h>
-#include <asm/unwind.h>
-
-	.text
-	.align	5
-	.word	0
-/*
- * Align the pointer in r0.  r3 contains the number of bytes that we are
- * mis-aligned by, and r1 is the number of bytes.  If r1 < 4, then we
- * don't bother; we use byte stores instead.
- */
-UNWIND(	.fnstart			)
-1:	subs	r1, r1, #4		@ 1 do we have enough
-	blt	5f			@ 1 bytes to align with?
-	cmp	r3, #2			@ 1
-	strltb	r2, [r0], #1		@ 1
-	strleb	r2, [r0], #1		@ 1
-	strb	r2, [r0], #1		@ 1
-	add	r1, r1, r3		@ 1 (r1 = r1 - (4 - r3))
-/*
- * The pointer is now aligned and the length is adjusted.  Try doing the
- * memzero again.
- */
-
-ENTRY(__memzero)
-	mov	r2, #0			@ 1
-	ands	r3, r0, #3		@ 1 unaligned?
-	bne	1b			@ 1
-/*
- * r3 = 0, and we know that the pointer in r0 is aligned to a word boundary.
- */
-	cmp	r1, #16			@ 1 we can skip this chunk if we
-	blt	4f			@ 1 have < 16 bytes
-
-#if ! CALGN(1)+0
-
-/*
- * We need an extra register for this loop - save the return address and
- * use the LR
- */
-	str	lr, [sp, #-4]!		@ 1
-UNWIND(	.fnend				)
-UNWIND(	.fnstart			)
-UNWIND(	.save 	{lr}			)
-	mov	ip, r2			@ 1
-	mov	lr, r2			@ 1
-
-3:	subs	r1, r1, #64		@ 1 write 32 bytes out per loop
-	stmgeia	r0!, {r2, r3, ip, lr}	@ 4
-	stmgeia	r0!, {r2, r3, ip, lr}	@ 4
-	stmgeia	r0!, {r2, r3, ip, lr}	@ 4
-	stmgeia	r0!, {r2, r3, ip, lr}	@ 4
-	bgt	3b			@ 1
-	ldmeqfd	sp!, {pc}		@ 1/2 quick exit
-/*
- * No need to correct the count; we're only testing bits from now on
- */
-	tst	r1, #32			@ 1
-	stmneia	r0!, {r2, r3, ip, lr}	@ 4
-	stmneia	r0!, {r2, r3, ip, lr}	@ 4
-	tst	r1, #16			@ 1 16 bytes or more?
-	stmneia	r0!, {r2, r3, ip, lr}	@ 4
-	ldr	lr, [sp], #4		@ 1
-UNWIND(	.fnend				)
-
-#else
-
-/*
- * This version aligns the destination pointer in order to write
- * whole cache lines at once.
- */
-
-	stmfd	sp!, {r4-r7, lr}
-UNWIND(	.fnend		       )
-UNWIND(	.fnstart	       )
-UNWIND(	.save 	{r4-r7, lr}    )
-	mov	r4, r2
-	mov	r5, r2
-	mov	r6, r2
-	mov	r7, r2
-	mov	ip, r2
-	mov	lr, r2
-
-	cmp	r1, #96
-	andgts	ip, r0, #31
-	ble	3f
-
-	rsb	ip, ip, #32
-	sub	r1, r1, ip
-	movs	ip, ip, lsl #(32 - 4)
-	stmcsia	r0!, {r4, r5, r6, r7}
-	stmmiia	r0!, {r4, r5}
-	movs	ip, ip, lsl #2
-	strcs	r2, [r0], #4
-
-3:	subs	r1, r1, #64
-	stmgeia	r0!, {r2-r7, ip, lr}
-	stmgeia	r0!, {r2-r7, ip, lr}
-	bgt	3b
-	ldmeqfd	sp!, {r4-r7, pc}
-
-	tst	r1, #32
-	stmneia	r0!, {r2-r7, ip, lr}
-	tst	r1, #16
-	stmneia	r0!, {r4-r7}
-	ldmfd	sp!, {r4-r7, lr}
-UNWIND(	.fnend		       )
-
-#endif
-
-UNWIND(	.fnstart			)
-4:	tst	r1, #8			@ 1 8 bytes or more?
-	stmneia	r0!, {r2, r3}		@ 2
-	tst	r1, #4			@ 1 4 bytes or more?
-	strne	r2, [r0], #4		@ 1
-/*
- * When we get here, we've got less than 4 bytes to zero.  We
- * may have an unaligned pointer as well.
- */
-5:	tst	r1, #2			@ 1 2 bytes or more?
-	strneb	r2, [r0], #1		@ 1
-	strneb	r2, [r0], #1		@ 1
-	tst	r1, #1			@ 1 a byte left over
-	strneb	r2, [r0], #1		@ 1
-	ret	lr			@ 1
-UNWIND(	.fnend				)
-ENDPROC(__memzero)