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riscv: memcpy_noalignment: Reorder to store via a3, then bump a3

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Rewrite the copy micro-step from:

    REG_L  a4, 0(a5)
    addi   a3, a3, SZREG
    addi   a5, a5, SZREG
    REG_S  a4, -SZREG(a3)

to:

    REG_L  a4, 0(a5)
    addi   a5, a5, SZREG
    REG_S  a4, 0(a3)
    addi   a3, a3, SZREG

Semantics are unchanged: both read *(a5_old), write *(a3_old), and then
increment a3/a5 by SZREG. memcpy assumes non-overlapping regions, so the
reordering preserves correctness.

No functional change.

Signed-off-by: Yao Zihong <zihong.plct@isrc.iscas.ac.cn>
Reviewed-by: Peter Bergner <bergner@tenstorrent.com>
This commit is contained in:
Yao Zihong
2025-10-30 17:49:21 -05:00
committed by Peter Bergner
parent 0698fd462a
commit 09a94c86ca
1 changed files with 2 additions and 2 deletions
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4
sysdeps/riscv/multiarch/memcpy_noalignment.S
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@@ -109,9 +109,9 @@ L(word_copy):
mv a5, a1
L(word_copy_loop):
REG_L a4, 0(a5)
addi a3, a3, SZREG
addi a5, a5, SZREG
REG_S a4, -SZREG(a3)
REG_S a4, 0(a3)
addi a3, a3, SZREG
bne a3, a6, L(word_copy_loop)
add a1, a1, a7
andi a2, a2, SZREG-1