riscv: Optimize vector registers initialization

This patch optimizes the initialization or invalidation of vector
registers. It can reduce the code sizes of vector_flush_cpu_state()
and reset_regs().

Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Han-Kuan Chen <hankuan.chen@sifive.com>

arch/riscv/kernel/head.S

@@ -375,39 +375,11 @@ ENTRY(reset_regs)
 
 	li	t1, SR_VS
 	csrs	CSR_STATUS, t1
-	vsetvli t1, x0, e8, m1
+	vsetvli t1, x0, e8, m8
 	vmv.v.i v0, 0
-	vmv.v.i v1, 0
-	vmv.v.i v2, 0
-	vmv.v.i v3, 0
-	vmv.v.i v4, 0
-	vmv.v.i v5, 0
-	vmv.v.i v6, 0
-	vmv.v.i v7, 0
 	vmv.v.i v8, 0
-	vmv.v.i v9, 0
-	vmv.v.i v10, 0
-	vmv.v.i v11, 0
-	vmv.v.i v12, 0
-	vmv.v.i v13, 0
-	vmv.v.i v14, 0
-	vmv.v.i v15, 0
 	vmv.v.i v16, 0
-	vmv.v.i v17, 0
-	vmv.v.i v18, 0
-	vmv.v.i v19, 0
-	vmv.v.i v20, 0
-	vmv.v.i v21, 0
-	vmv.v.i v22, 0
-	vmv.v.i v23, 0
 	vmv.v.i v24, 0
-	vmv.v.i v25, 0
-	vmv.v.i v26, 0
-	vmv.v.i v27, 0
-	vmv.v.i v28, 0
-	vmv.v.i v29, 0
-	vmv.v.i v30, 0
-	vmv.v.i v31, 0
 	/* note that the caller must clear SR_VS */
 #endif /* CONFIG_VECTOR */
 

arch/riscv/kernel/kernel_mode_vector.c

@@ -86,39 +86,11 @@ static void vector_flush_cpu_state(void)
 	long tmp;
 
 	__asm__ __volatile__ (
-		"vsetvli %0, x0, e8, m1\n"
+		"vsetvli %0, x0, e8, m8\n"
 		"vmv.v.i v0, 0\n"
-		"vmv.v.i v1, 0\n"
-		"vmv.v.i v2, 0\n"
-		"vmv.v.i v3, 0\n"
-		"vmv.v.i v4, 0\n"
-		"vmv.v.i v5, 0\n"
-		"vmv.v.i v6, 0\n"
-		"vmv.v.i v7, 0\n"
 		"vmv.v.i v8, 0\n"
-		"vmv.v.i v9, 0\n"
-		"vmv.v.i v10, 0\n"
-		"vmv.v.i v11, 0\n"
-		"vmv.v.i v12, 0\n"
-		"vmv.v.i v13, 0\n"
-		"vmv.v.i v14, 0\n"
-		"vmv.v.i v15, 0\n"
 		"vmv.v.i v16, 0\n"
-		"vmv.v.i v17, 0\n"
-		"vmv.v.i v18, 0\n"
-		"vmv.v.i v19, 0\n"
-		"vmv.v.i v20, 0\n"
-		"vmv.v.i v21, 0\n"
-		"vmv.v.i v22, 0\n"
-		"vmv.v.i v23, 0\n"
-		"vmv.v.i v24, 0\n"
-		"vmv.v.i v25, 0\n"
-		"vmv.v.i v26, 0\n"
-		"vmv.v.i v27, 0\n"
-		"vmv.v.i v28, 0\n"
-		"vmv.v.i v29, 0\n"
-		"vmv.v.i v30, 0\n"
-		"vmv.v.i v31, 0\n":"=r"(tmp)::);
+		"vmv.v.i v24, 0\n":"=r"(tmp)::);
 }
 
 /*