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https://github.com/AsahiLinux/u-boot
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riscv: Fix memmove and optimise memcpy when misalign
At present U-Boot SPL fails to boot on SiFive Unleashed board, due to a load address misaligned exception happens when loading the FIT image in spl_load_simple_fit(). The exception happens in memmove() which is called by fdt_splice_(). Commit8f0dc4cfd1introduces an assembly version of memmove but it does take misalignment into account (it checks if length is a multiple of machine word size but pointers need also be aligned). As a result it will generate misaligned load/store for the majority of cases and causes significant performance regression on hardware that traps misaligned load/store and emulate them using firmware. The current behaviour of memcpy is that it checks if both src and dest pointers are co-aligned (aka congruent modular SZ_REG). If aligned, it will copy data word-by-word after first aligning pointers to word boundary. If src and dst are not co-aligned, however, byte-wise copy will be performed. This patch was taken from the Linux kernel patch [1], which has not been applied at the time being. It fixes the memmove and optimises memcpy for misaligned cases. It will first align destination pointer to word-boundary regardless whether src and dest are co-aligned or not. If they indeed are, then wordwise copy is performed. If they are not co-aligned, then it will load two adjacent words from src and use shifts to assemble a full machine word. Some additional assembly level micro-optimisation is also performed to ensure more instructions can be compressed (e.g. prefer a0 to t6). With this patch, U-Boot boots again on SiFive Unleashed board. [1] https://patchwork.kernel.org/project/linux-riscv/patch/20210216225555.4976-1-gary@garyguo.net/ Fixes:8f0dc4cfd1("riscv: assembler versions of memcpy, memmove, memset") Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
This commit is contained in:
Bin Meng
Leo Yu-Chi Liang
parent
e90cb0db34
commit
703b84ec29
2 changed files with 248 additions and 133 deletions
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@ -9,100 +9,151 @@
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/* void *memcpy(void *, const void *, size_t) */
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ENTRY(__memcpy)
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WEAK(memcpy)
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move t6, a0 /* Preserve return value */
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/* Save for return value */
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mv t6, a0
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/* Defer to byte-oriented copy for small sizes */
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sltiu a3, a2, 128
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bnez a3, 4f
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/* Use word-oriented copy only if low-order bits match */
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andi a3, t6, SZREG-1
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andi a4, a1, SZREG-1
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bne a3, a4, 4f
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beqz a3, 2f /* Skip if already aligned */
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/*
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* Round to nearest double word-aligned address
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* greater than or equal to start address
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* Register allocation for code below:
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* a0 - start of uncopied dst
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* a1 - start of uncopied src
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* t0 - end of uncopied dst
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*/
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andi a3, a1, ~(SZREG-1)
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addi a3, a3, SZREG
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/* Handle initial misalignment */
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sub a4, a3, a1
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add t0, a0, a2
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/*
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* Use bytewise copy if too small.
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*
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* This threshold must be at least 2*SZREG to ensure at least one
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* wordwise copy is performed. It is chosen to be 16 because it will
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* save at least 7 iterations of bytewise copy, which pays off the
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* fixed overhead.
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*/
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li a3, 16
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bltu a2, a3, .Lbyte_copy_tail
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/*
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* Bytewise copy first to align a0 to word boundary.
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*/
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addi a2, a0, SZREG-1
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andi a2, a2, ~(SZREG-1)
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beq a0, a2, 2f
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1:
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lb a5, 0(a1)
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addi a1, a1, 1
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sb a5, 0(t6)
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addi t6, t6, 1
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bltu a1, a3, 1b
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sub a2, a2, a4 /* Update count */
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lb a5, 0(a1)
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addi a1, a1, 1
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sb a5, 0(a0)
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addi a0, a0, 1
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bne a0, a2, 1b
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2:
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andi a4, a2, ~((16*SZREG)-1)
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beqz a4, 4f
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add a3, a1, a4
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3:
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REG_L a4, 0(a1)
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REG_L a5, SZREG(a1)
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REG_L a6, 2*SZREG(a1)
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REG_L a7, 3*SZREG(a1)
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REG_L t0, 4*SZREG(a1)
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REG_L t1, 5*SZREG(a1)
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REG_L t2, 6*SZREG(a1)
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REG_L t3, 7*SZREG(a1)
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REG_L t4, 8*SZREG(a1)
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REG_L t5, 9*SZREG(a1)
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REG_S a4, 0(t6)
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REG_S a5, SZREG(t6)
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REG_S a6, 2*SZREG(t6)
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REG_S a7, 3*SZREG(t6)
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REG_S t0, 4*SZREG(t6)
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REG_S t1, 5*SZREG(t6)
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REG_S t2, 6*SZREG(t6)
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REG_S t3, 7*SZREG(t6)
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REG_S t4, 8*SZREG(t6)
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REG_S t5, 9*SZREG(t6)
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REG_L a4, 10*SZREG(a1)
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REG_L a5, 11*SZREG(a1)
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REG_L a6, 12*SZREG(a1)
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REG_L a7, 13*SZREG(a1)
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REG_L t0, 14*SZREG(a1)
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REG_L t1, 15*SZREG(a1)
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addi a1, a1, 16*SZREG
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REG_S a4, 10*SZREG(t6)
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REG_S a5, 11*SZREG(t6)
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REG_S a6, 12*SZREG(t6)
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REG_S a7, 13*SZREG(t6)
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REG_S t0, 14*SZREG(t6)
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REG_S t1, 15*SZREG(t6)
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addi t6, t6, 16*SZREG
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bltu a1, a3, 3b
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andi a2, a2, (16*SZREG)-1 /* Update count */
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4:
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/* Handle trailing misalignment */
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beqz a2, 6f
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add a3, a1, a2
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/*
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* Now a0 is word-aligned. If a1 is also word aligned, we could perform
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* aligned word-wise copy. Otherwise we need to perform misaligned
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* word-wise copy.
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*/
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andi a3, a1, SZREG-1
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bnez a3, .Lmisaligned_word_copy
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/* Use word-oriented copy if co-aligned to word boundary */
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or a5, a1, t6
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or a5, a5, a3
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andi a5, a5, 3
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bnez a5, 5f
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7:
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lw a4, 0(a1)
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addi a1, a1, 4
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sw a4, 0(t6)
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addi t6, t6, 4
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bltu a1, a3, 7b
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/* Unrolled wordwise copy */
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addi t0, t0, -(16*SZREG-1)
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bgeu a0, t0, 2f
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1:
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REG_L a2, 0(a1)
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REG_L a3, SZREG(a1)
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REG_L a4, 2*SZREG(a1)
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REG_L a5, 3*SZREG(a1)
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REG_L a6, 4*SZREG(a1)
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REG_L a7, 5*SZREG(a1)
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REG_L t1, 6*SZREG(a1)
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REG_L t2, 7*SZREG(a1)
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REG_L t3, 8*SZREG(a1)
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REG_L t4, 9*SZREG(a1)
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REG_L t5, 10*SZREG(a1)
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REG_S a2, 0(a0)
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REG_S a3, SZREG(a0)
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REG_S a4, 2*SZREG(a0)
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REG_S a5, 3*SZREG(a0)
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REG_S a6, 4*SZREG(a0)
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REG_S a7, 5*SZREG(a0)
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REG_S t1, 6*SZREG(a0)
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REG_S t2, 7*SZREG(a0)
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REG_S t3, 8*SZREG(a0)
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REG_S t4, 9*SZREG(a0)
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REG_S t5, 10*SZREG(a0)
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REG_L a2, 11*SZREG(a1)
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REG_L a3, 12*SZREG(a1)
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REG_L a4, 13*SZREG(a1)
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REG_L a5, 14*SZREG(a1)
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REG_L a6, 15*SZREG(a1)
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addi a1, a1, 16*SZREG
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REG_S a2, 11*SZREG(a0)
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REG_S a3, 12*SZREG(a0)
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REG_S a4, 13*SZREG(a0)
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REG_S a5, 14*SZREG(a0)
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REG_S a6, 15*SZREG(a0)
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addi a0, a0, 16*SZREG
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bltu a0, t0, 1b
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2:
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/* Post-loop increment by 16*SZREG-1 and pre-loop decrement by SZREG-1 */
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addi t0, t0, 15*SZREG
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/* Wordwise copy */
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bgeu a0, t0, 2f
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1:
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REG_L a5, 0(a1)
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addi a1, a1, SZREG
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REG_S a5, 0(a0)
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addi a0, a0, SZREG
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bltu a0, t0, 1b
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2:
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addi t0, t0, SZREG-1
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.Lbyte_copy_tail:
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/*
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* Bytewise copy anything left.
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*/
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beq a0, t0, 2f
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1:
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lb a5, 0(a1)
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addi a1, a1, 1
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sb a5, 0(a0)
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addi a0, a0, 1
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bne a0, t0, 1b
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2:
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mv a0, t6
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ret
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5:
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lb a4, 0(a1)
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addi a1, a1, 1
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sb a4, 0(t6)
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addi t6, t6, 1
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bltu a1, a3, 5b
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6:
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ret
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.Lmisaligned_word_copy:
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/*
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* Misaligned word-wise copy.
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* For misaligned copy we still perform word-wise copy, but we need to
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* use the value fetched from the previous iteration and do some shifts.
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* This is safe because we wouldn't access more words than necessary.
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*/
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/* Calculate shifts */
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slli t3, a3, 3
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sub t4, x0, t3 /* negate is okay as shift will only look at LSBs */
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/* Load the initial value and align a1 */
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andi a1, a1, ~(SZREG-1)
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REG_L a5, 0(a1)
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addi t0, t0, -(SZREG-1)
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/* At least one iteration will be executed here, no check */
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1:
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srl a4, a5, t3
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REG_L a5, SZREG(a1)
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addi a1, a1, SZREG
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sll a2, a5, t4
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or a2, a2, a4
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REG_S a2, 0(a0)
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addi a0, a0, SZREG
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bltu a0, t0, 1b
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/* Update pointers to correct value */
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addi t0, t0, SZREG-1
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add a1, a1, a3
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j .Lbyte_copy_tail
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END(__memcpy)
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@ -5,60 +5,124 @@
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ENTRY(__memmove)
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WEAK(memmove)
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move t0, a0
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move t1, a1
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/*
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* Here we determine if forward copy is possible. Forward copy is
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* preferred to backward copy as it is more cache friendly.
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*
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* If a0 >= a1, t0 gives their distance, if t0 >= a2 then we can
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* copy forward.
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* If a0 < a1, we can always copy forward. This will make t0 negative,
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* so a *unsigned* comparison will always have t0 >= a2.
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*
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* For forward copy we just delegate the task to memcpy.
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*/
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sub t0, a0, a1
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bltu t0, a2, 1f
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tail __memcpy
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1:
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beq a0, a1, exit_memcpy
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beqz a2, exit_memcpy
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srli t2, a2, 0x2
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/*
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* Register allocation for code below:
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* a0 - end of uncopied dst
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* a1 - end of uncopied src
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* t0 - start of uncopied dst
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*/
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mv t0, a0
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add a0, a0, a2
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add a1, a1, a2
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slt t3, a0, a1
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beqz t3, do_reverse
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/*
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* Use bytewise copy if too small.
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*
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* This threshold must be at least 2*SZREG to ensure at least one
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* wordwise copy is performed. It is chosen to be 16 because it will
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* save at least 7 iterations of bytewise copy, which pays off the
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* fixed overhead.
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*/
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li a3, 16
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bltu a2, a3, .Lbyte_copy_tail
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andi a2, a2, 0x3
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li t4, 1
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beqz t2, byte_copy
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/*
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* Bytewise copy first to align t0 to word boundary.
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*/
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andi a2, a0, ~(SZREG-1)
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beq a0, a2, 2f
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1:
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addi a1, a1, -1
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lb a5, 0(a1)
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addi a0, a0, -1
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sb a5, 0(a0)
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bne a0, a2, 1b
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2:
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word_copy:
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lw t3, 0(a1)
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addi t2, t2, -1
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addi a1, a1, 4
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sw t3, 0(a0)
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addi a0, a0, 4
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bnez t2, word_copy
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beqz a2, exit_memcpy
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j byte_copy
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/*
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* Now a0 is word-aligned. If a1 is also word aligned, we could perform
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* aligned word-wise copy. Otherwise we need to perform misaligned
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* word-wise copy.
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*/
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andi a3, a1, SZREG-1
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bnez a3, .Lmisaligned_word_copy
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do_reverse:
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add a0, a0, a2
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add a1, a1, a2
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andi a2, a2, 0x3
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li t4, -1
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beqz t2, reverse_byte_copy
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/* Wordwise copy */
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addi t0, t0, SZREG-1
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bleu a0, t0, 2f
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1:
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addi a1, a1, -SZREG
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REG_L a5, 0(a1)
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addi a0, a0, -SZREG
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REG_S a5, 0(a0)
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bgtu a0, t0, 1b
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2:
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addi t0, t0, -(SZREG-1)
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reverse_word_copy:
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addi a1, a1, -4
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addi t2, t2, -1
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lw t3, 0(a1)
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addi a0, a0, -4
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sw t3, 0(a0)
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bnez t2, reverse_word_copy
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beqz a2, exit_memcpy
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.Lbyte_copy_tail:
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/*
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* Bytewise copy anything left.
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*/
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beq a0, t0, 2f
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1:
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addi a1, a1, -1
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lb a5, 0(a1)
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addi a0, a0, -1
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sb a5, 0(a0)
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bne a0, t0, 1b
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2:
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reverse_byte_copy:
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addi a0, a0, -1
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addi a1, a1, -1
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mv a0, t0
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ret
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byte_copy:
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lb t3, 0(a1)
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addi a2, a2, -1
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sb t3, 0(a0)
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add a1, a1, t4
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add a0, a0, t4
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bnez a2, byte_copy
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.Lmisaligned_word_copy:
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/*
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* Misaligned word-wise copy.
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* For misaligned copy we still perform word-wise copy, but we need to
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* use the value fetched from the previous iteration and do some shifts.
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* This is safe because we wouldn't access more words than necessary.
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*/
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/* Calculate shifts */
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slli t3, a3, 3
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sub t4, x0, t3 /* negate is okay as shift will only look at LSBs */
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/* Load the initial value and align a1 */
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andi a1, a1, ~(SZREG-1)
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REG_L a5, 0(a1)
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addi t0, t0, SZREG-1
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/* At least one iteration will be executed here, no check */
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1:
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sll a4, a5, t4
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addi a1, a1, -SZREG
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REG_L a5, 0(a1)
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srl a2, a5, t3
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or a2, a2, a4
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addi a0, a0, -SZREG
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REG_S a2, 0(a0)
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bgtu a0, t0, 1b
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/* Update pointers to correct value */
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addi t0, t0, -(SZREG-1)
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add a1, a1, a3
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j .Lbyte_copy_tail
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exit_memcpy:
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move a0, t0
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move a1, t1
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ret
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END(__memmove)
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