Add a "fork" of musl as //fusl.

fusl/src/string/armel/memcpy.s

+/*
+ * 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.
+ */
+
+.syntax unified
+
+.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 */
+        ldrbmi r3, [r1], #1
+        ldrbcs r4, [r1], #1
+        ldrbcs r12,[r1], #1
+        strbmi r3, [r0], #1
+        strbcs r4, [r0], #1
+        strbcs 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
+        ldmcs   r1!, {r4, r5, r6, r7}           /* 16 bytes */
+        ldmmi   r1!, {r8, r9}                   /*  8 bytes */
+        stmcs   r0!, {r4, r5, r6, r7}
+        stmmi   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
+        ldmcs   r1!, {r4, r5, r6, r7}           /* 16 bytes */
+        ldmmi   r1!, {r8, r9}                   /*  8 bytes */
+        stmcs   r0!, {r4, r5, r6, r7}
+        stmmi   r0!, {r8, r9}
+        movs    r12, r2, lsl #30
+        ldrcs   r3, [r1], #4                    /*  4 bytes */
+        ldrhmi r4, [r1], #2                     /*  2 bytes */
+        strcs   r3, [r0], #4
+        strhmi r4, [r0], #2
+        tst     r2, #0x1
+        ldrbne r3, [r1]                         /*  last byte  */
+        strbne r3, [r0]
+
+        /* we're done! restore everything and return */
+1:      ldmfd   sp!, {r5-r11}
+        ldmfd   sp!, {r0, r4, 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
+        strbmi r3, [r0], #1
+        movmi   r3, r3, lsr #8
+        strbcs r3, [r0], #1
+        movcs   r3, r3, lsr #8
+        strbcs 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)
+        strbmi r3, [r0], #1
+        movmi   r3, r3, lsr #8
+        strbcs r3, [r0], #1
+        movcs   r3, r3, lsr #8
+        strbcs 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 */
+        ldrbmi r2, [r1], #1
+        ldrbcs r3, [r1], #1
+        ldrbcs r12,[r1]
+        strbmi r2, [r0], #1
+        strbcs r3, [r0], #1
+        strbcs r12,[r0]
+
+        /* we're done! restore sp and spilled registers and return */
+        add     sp,  sp, #28
+        ldmfd   sp!, {r0, r4, lr}
+        bx      lr