[PATCH v2 1/3] riscv: memcpy_noalignment: Make register allocation Zca-friendly

[Yao Zihong]

Tidy the temporary register allocation to favor registers eligible for
compressed encodings when Zca/Zcb are enabled, and to slightly shorten
live ranges. This keeps the ABI and clobber set unchanged and does not
alter control flow or memory access behavior.

Motivation:
* RISC-V compressed encodings prefer a subset of integer registers.
  Using them where legal improves code density when Zc* is enabled.
* Shorter live ranges also help the assembler choose compressed forms.

Details:
* Remap temporaries to Zca-friendly registers where possible.
* Keep argument registers and callee-saved semantics unchanged.
* No change to barriers, aliasing, or loop structure.

No functional change.

sysdeps/riscv/multiarch/memcpy_noalignment.S: Reassign temps to improve
compressed encoding opportunities; reduce unnecessary live ranges.

Signed-off-by: Yao Zihong <zihong.plct@isrc.iscas.ac.cn>
---
 sysdeps/riscv/multiarch/memcpy_noalignment.S | 34 ++++++++++----------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/sysdeps/riscv/multiarch/memcpy_noalignment.S b/sysdeps/riscv/multiarch/memcpy_noalignment.S
index dd135f4a4d..e319b710c2 100644
--- a/sysdeps/riscv/multiarch/memcpy_noalignment.S
+++ b/sysdeps/riscv/multiarch/memcpy_noalignment.S
@@ -121,10 +121,10 @@ L(word_copy_loop):
 	andi	a2, a2, SZREG-1
 
 	/* Copy the last word unaligned.  */
-	add	a3, a1, a2
-	add	a4, a6, a2
-	REG_L	t0, -SZREG(a3)
-	REG_S	t0, -SZREG(a4)
+	add	a1, a1, a2
+	add	a2, a6, a2
+	REG_L	a3, -SZREG(a1)
+	REG_S	a3, -SZREG(a2)
 	ret
 
 L(tail):
@@ -133,24 +133,24 @@ L(tail):
 	add	a3, a1, a2
 	add	a4, a6, a2
 	beq	a5, zero, L(copy_0_3)
-	lw	t0, 0(a1)
-	lw	t1, -4(a3)
-	sw	t0, 0(a6)
-	sw	t1, -4(a4)
+	lw	a2, 0(a1)
+	lw	a5, -4(a3)
+	sw	a2, 0(a6)
+	sw	a5, -4(a4)
 	ret
 
 	/* Copy 0-3 bytes.  */
 L(copy_0_3):
 	beq	a2, zero, L(ret)
-	srli    a2, a2, 1
-	add     t4, a1, a2
-	add     t5, a6, a2
-	lbu     t0, 0(a1)
-	lbu     t1, -1(a3)
-	lbu     t2, 0(t4)
-	sb      t0, 0(a6)
-	sb      t1, -1(a4)
-	sb      t2, 0(t5)
+	lbu	a3, -1(a3)
+	srli	a2, a2, 1
+	add	a5, a1, a2
+	lbu	a1, 0(a1)
+	sb	a3, -1(a4)
+	lbu	a4, 0(a5)
+	add 	a2, a6, a2
+	sb	a1, 0(a6)
+	sb	a4, 0(a2)
 L(ret):
 	ret
 L(tail_adjust):
-- 
2.47.2