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authorRich Felker <dalias@aerifal.cx>2013-08-14 03:06:21 -0400
committerRich Felker <dalias@aerifal.cx>2013-08-14 03:06:21 -0400
commitcccc1844be95549e5b6c91ffc1f2c2ba3d3aab16 (patch)
treebf9cd7643d50131983f17d4631432b70db274d9c /src/string
parentfb72a97df9222be61ec582ba7b1e9ce496b65e3e (diff)
downloadmusl-cccc1844be95549e5b6c91ffc1f2c2ba3d3aab16.tar.gz
add arm-optimized memcpy implementation from bionic libc
the approach of this implementation was heavily investigated prior to adopting it. attempts to obtain similar performance with pure C code were capping out at about 75% of the performance of the asm, with considerably larger code size, and were fragile in that the compiler would sometimes compile part of memcpy into a call to itself. therefore, just using the asm seems to be the best option. this commit is the first to make use of the new subarch-specific asm framework. the new armel directory is the location for arm asm that should not be used for all arm subarchs, only the default one. armhf is the name of the little-endian hardfloat-ABI subarch, which can use the exact same asm. in both cases, the build system finds the asm by following a memcpy.sub file. the other two subarchs, armeb and armebhf, would need a big-endian variant of this code. it would not be hard to adapt the code to big endian, but I will hold off on doing so until there is demand for it.
Diffstat (limited to 'src/string')
-rw-r--r--src/string/armel/memcpy.s381
-rw-r--r--src/string/armel/memcpy.sub1
-rw-r--r--src/string/armhf/memcpy.sub1
3 files changed, 383 insertions, 0 deletions
diff --git a/src/string/armel/memcpy.s b/src/string/armel/memcpy.s
new file mode 100644
index 00000000..9f24a4f3
--- /dev/null
+++ b/src/string/armel/memcpy.s
@@ -0,0 +1,381 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+
+/*
+ * Optimized memcpy() for ARM.
+ *
+ * note that memcpy() always returns the destination pointer,
+ * so we have to preserve R0.
+ */
+
+/*
+ * This file has been modified from the original for use in musl libc.
+ * The main changes are: addition of .type memcpy,%function to make the
+ * code safely callable from thumb mode, adjusting the return
+ * instructions to be compatible with pre-thumb ARM cpus, and removal
+ * of prefetch code that is not compatible with older cpus.
+ */
+
+.global memcpy
+.type memcpy,%function
+memcpy:
+ /* The stack must always be 64-bits aligned to be compliant with the
+ * ARM ABI. Since we have to save R0, we might as well save R4
+ * which we can use for better pipelining of the reads below
+ */
+ .fnstart
+ .save {r0, r4, lr}
+ stmfd sp!, {r0, r4, lr}
+ /* Making room for r5-r11 which will be spilled later */
+ .pad #28
+ sub sp, sp, #28
+
+ /* it simplifies things to take care of len<4 early */
+ cmp r2, #4
+ blo copy_last_3_and_return
+
+ /* compute the offset to align the source
+ * offset = (4-(src&3))&3 = -src & 3
+ */
+ rsb r3, r1, #0
+ ands r3, r3, #3
+ beq src_aligned
+
+ /* align source to 32 bits. We need to insert 2 instructions between
+ * a ldr[b|h] and str[b|h] because byte and half-word instructions
+ * stall 2 cycles.
+ */
+ movs r12, r3, lsl #31
+ sub r2, r2, r3 /* we know that r3 <= r2 because r2 >= 4 */
+ ldrmib r3, [r1], #1
+ ldrcsb r4, [r1], #1
+ ldrcsb r12,[r1], #1
+ strmib r3, [r0], #1
+ strcsb r4, [r0], #1
+ strcsb r12,[r0], #1
+
+src_aligned:
+
+ /* see if src and dst are aligned together (congruent) */
+ eor r12, r0, r1
+ tst r12, #3
+ bne non_congruent
+
+ /* Use post-incriment mode for stm to spill r5-r11 to reserved stack
+ * frame. Don't update sp.
+ */
+ stmea sp, {r5-r11}
+
+ /* align the destination to a cache-line */
+ rsb r3, r0, #0
+ ands r3, r3, #0x1C
+ beq congruent_aligned32
+ cmp r3, r2
+ andhi r3, r2, #0x1C
+
+ /* conditionnaly copies 0 to 7 words (length in r3) */
+ movs r12, r3, lsl #28
+ ldmcsia r1!, {r4, r5, r6, r7} /* 16 bytes */
+ ldmmiia r1!, {r8, r9} /* 8 bytes */
+ stmcsia r0!, {r4, r5, r6, r7}
+ stmmiia r0!, {r8, r9}
+ tst r3, #0x4
+ ldrne r10,[r1], #4 /* 4 bytes */
+ strne r10,[r0], #4
+ sub r2, r2, r3
+
+congruent_aligned32:
+ /*
+ * here source is aligned to 32 bytes.
+ */
+
+cached_aligned32:
+ subs r2, r2, #32
+ blo less_than_32_left
+
+ /*
+ * We preload a cache-line up to 64 bytes ahead. On the 926, this will
+ * stall only until the requested world is fetched, but the linefill
+ * continues in the the background.
+ * While the linefill is going, we write our previous cache-line
+ * into the write-buffer (which should have some free space).
+ * When the linefill is done, the writebuffer will
+ * start dumping its content into memory
+ *
+ * While all this is going, we then load a full cache line into
+ * 8 registers, this cache line should be in the cache by now
+ * (or partly in the cache).
+ *
+ * This code should work well regardless of the source/dest alignment.
+ *
+ */
+
+ /* Align the preload register to a cache-line because the cpu does
+ * "critical word first" (the first word requested is loaded first).
+ */
+ @ bic r12, r1, #0x1F
+ @ add r12, r12, #64
+
+1: ldmia r1!, { r4-r11 }
+ subs r2, r2, #32
+
+ /*
+ * NOTE: if r12 is more than 64 ahead of r1, the following ldrhi
+ * for ARM9 preload will not be safely guarded by the preceding subs.
+ * When it is safely guarded the only possibility to have SIGSEGV here
+ * is because the caller overstates the length.
+ */
+ @ ldrhi r3, [r12], #32 /* cheap ARM9 preload */
+ stmia r0!, { r4-r11 }
+ bhs 1b
+
+ add r2, r2, #32
+
+less_than_32_left:
+ /*
+ * less than 32 bytes left at this point (length in r2)
+ */
+
+ /* skip all this if there is nothing to do, which should
+ * be a common case (if not executed the code below takes
+ * about 16 cycles)
+ */
+ tst r2, #0x1F
+ beq 1f
+
+ /* conditionnaly copies 0 to 31 bytes */
+ movs r12, r2, lsl #28
+ ldmcsia r1!, {r4, r5, r6, r7} /* 16 bytes */
+ ldmmiia r1!, {r8, r9} /* 8 bytes */
+ stmcsia r0!, {r4, r5, r6, r7}
+ stmmiia r0!, {r8, r9}
+ movs r12, r2, lsl #30
+ ldrcs r3, [r1], #4 /* 4 bytes */
+ ldrmih r4, [r1], #2 /* 2 bytes */
+ strcs r3, [r0], #4
+ strmih r4, [r0], #2
+ tst r2, #0x1
+ ldrneb r3, [r1] /* last byte */
+ strneb r3, [r0]
+
+ /* we're done! restore everything and return */
+1: ldmfd sp!, {r5-r11}
+ ldmfd sp!, {r0, r4, lr}
+ tst lr, #1
+ moveq pc, lr
+ bx lr
+
+ /********************************************************************/
+
+non_congruent:
+ /*
+ * here source is aligned to 4 bytes
+ * but destination is not.
+ *
+ * in the code below r2 is the number of bytes read
+ * (the number of bytes written is always smaller, because we have
+ * partial words in the shift queue)
+ */
+ cmp r2, #4
+ blo copy_last_3_and_return
+
+ /* Use post-incriment mode for stm to spill r5-r11 to reserved stack
+ * frame. Don't update sp.
+ */
+ stmea sp, {r5-r11}
+
+ /* compute shifts needed to align src to dest */
+ rsb r5, r0, #0
+ and r5, r5, #3 /* r5 = # bytes in partial words */
+ mov r12, r5, lsl #3 /* r12 = right */
+ rsb lr, r12, #32 /* lr = left */
+
+ /* read the first word */
+ ldr r3, [r1], #4
+ sub r2, r2, #4
+
+ /* write a partial word (0 to 3 bytes), such that destination
+ * becomes aligned to 32 bits (r5 = nb of words to copy for alignment)
+ */
+ movs r5, r5, lsl #31
+ strmib r3, [r0], #1
+ movmi r3, r3, lsr #8
+ strcsb r3, [r0], #1
+ movcs r3, r3, lsr #8
+ strcsb r3, [r0], #1
+ movcs r3, r3, lsr #8
+
+ cmp r2, #4
+ blo partial_word_tail
+
+ /* Align destination to 32 bytes (cache line boundary) */
+1: tst r0, #0x1c
+ beq 2f
+ ldr r5, [r1], #4
+ sub r2, r2, #4
+ orr r4, r3, r5, lsl lr
+ mov r3, r5, lsr r12
+ str r4, [r0], #4
+ cmp r2, #4
+ bhs 1b
+ blo partial_word_tail
+
+ /* copy 32 bytes at a time */
+2: subs r2, r2, #32
+ blo less_than_thirtytwo
+
+ /* Use immediate mode for the shifts, because there is an extra cycle
+ * for register shifts, which could account for up to 50% of
+ * performance hit.
+ */
+
+ cmp r12, #24
+ beq loop24
+ cmp r12, #8
+ beq loop8
+
+loop16:
+ ldr r12, [r1], #4
+1: mov r4, r12
+ ldmia r1!, { r5,r6,r7, r8,r9,r10,r11}
+ subs r2, r2, #32
+ ldrhs r12, [r1], #4
+ orr r3, r3, r4, lsl #16
+ mov r4, r4, lsr #16
+ orr r4, r4, r5, lsl #16
+ mov r5, r5, lsr #16
+ orr r5, r5, r6, lsl #16
+ mov r6, r6, lsr #16
+ orr r6, r6, r7, lsl #16
+ mov r7, r7, lsr #16
+ orr r7, r7, r8, lsl #16
+ mov r8, r8, lsr #16
+ orr r8, r8, r9, lsl #16
+ mov r9, r9, lsr #16
+ orr r9, r9, r10, lsl #16
+ mov r10, r10, lsr #16
+ orr r10, r10, r11, lsl #16
+ stmia r0!, {r3,r4,r5,r6, r7,r8,r9,r10}
+ mov r3, r11, lsr #16
+ bhs 1b
+ b less_than_thirtytwo
+
+loop8:
+ ldr r12, [r1], #4
+1: mov r4, r12
+ ldmia r1!, { r5,r6,r7, r8,r9,r10,r11}
+ subs r2, r2, #32
+ ldrhs r12, [r1], #4
+ orr r3, r3, r4, lsl #24
+ mov r4, r4, lsr #8
+ orr r4, r4, r5, lsl #24
+ mov r5, r5, lsr #8
+ orr r5, r5, r6, lsl #24
+ mov r6, r6, lsr #8
+ orr r6, r6, r7, lsl #24
+ mov r7, r7, lsr #8
+ orr r7, r7, r8, lsl #24
+ mov r8, r8, lsr #8
+ orr r8, r8, r9, lsl #24
+ mov r9, r9, lsr #8
+ orr r9, r9, r10, lsl #24
+ mov r10, r10, lsr #8
+ orr r10, r10, r11, lsl #24
+ stmia r0!, {r3,r4,r5,r6, r7,r8,r9,r10}
+ mov r3, r11, lsr #8
+ bhs 1b
+ b less_than_thirtytwo
+
+loop24:
+ ldr r12, [r1], #4
+1: mov r4, r12
+ ldmia r1!, { r5,r6,r7, r8,r9,r10,r11}
+ subs r2, r2, #32
+ ldrhs r12, [r1], #4
+ orr r3, r3, r4, lsl #8
+ mov r4, r4, lsr #24
+ orr r4, r4, r5, lsl #8
+ mov r5, r5, lsr #24
+ orr r5, r5, r6, lsl #8
+ mov r6, r6, lsr #24
+ orr r6, r6, r7, lsl #8
+ mov r7, r7, lsr #24
+ orr r7, r7, r8, lsl #8
+ mov r8, r8, lsr #24
+ orr r8, r8, r9, lsl #8
+ mov r9, r9, lsr #24
+ orr r9, r9, r10, lsl #8
+ mov r10, r10, lsr #24
+ orr r10, r10, r11, lsl #8
+ stmia r0!, {r3,r4,r5,r6, r7,r8,r9,r10}
+ mov r3, r11, lsr #24
+ bhs 1b
+
+less_than_thirtytwo:
+ /* copy the last 0 to 31 bytes of the source */
+ rsb r12, lr, #32 /* we corrupted r12, recompute it */
+ add r2, r2, #32
+ cmp r2, #4
+ blo partial_word_tail
+
+1: ldr r5, [r1], #4
+ sub r2, r2, #4
+ orr r4, r3, r5, lsl lr
+ mov r3, r5, lsr r12
+ str r4, [r0], #4
+ cmp r2, #4
+ bhs 1b
+
+partial_word_tail:
+ /* we have a partial word in the input buffer */
+ movs r5, lr, lsl #(31-3)
+ strmib r3, [r0], #1
+ movmi r3, r3, lsr #8
+ strcsb r3, [r0], #1
+ movcs r3, r3, lsr #8
+ strcsb r3, [r0], #1
+
+ /* Refill spilled registers from the stack. Don't update sp. */
+ ldmfd sp, {r5-r11}
+
+copy_last_3_and_return:
+ movs r2, r2, lsl #31 /* copy remaining 0, 1, 2 or 3 bytes */
+ ldrmib r2, [r1], #1
+ ldrcsb r3, [r1], #1
+ ldrcsb r12,[r1]
+ strmib r2, [r0], #1
+ strcsb r3, [r0], #1
+ strcsb r12,[r0]
+
+ /* we're done! restore sp and spilled registers and return */
+ add sp, sp, #28
+ ldmfd sp!, {r0, r4, lr}
+ tst lr, #1
+ moveq pc, lr
+ bx lr
diff --git a/src/string/armel/memcpy.sub b/src/string/armel/memcpy.sub
new file mode 100644
index 00000000..543f583f
--- /dev/null
+++ b/src/string/armel/memcpy.sub
@@ -0,0 +1 @@
+memcpy.s
diff --git a/src/string/armhf/memcpy.sub b/src/string/armhf/memcpy.sub
new file mode 100644
index 00000000..add0590c
--- /dev/null
+++ b/src/string/armhf/memcpy.sub
@@ -0,0 +1 @@
+../armel/memcpy.s