RISC-V: implement __lshrti3.

Signed-off-by: Alex Guo <xfguo@jlsemi.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/Makefile

@@ -26,6 +26,9 @@ ifeq ($(CONFIG_ARCH_RV64I),y)
 
 	KBUILD_CFLAGS += -mabi=lp64
 	KBUILD_AFLAGS += -mabi=lp64
+	
+	KBUILD_CFLAGS	+= $(call cc-ifversion, -ge, 0500, -DCONFIG_ARCH_SUPPORTS_INT128)
+
 	KBUILD_MARCH = rv64im
 	LDFLAGS += -melf64lriscv
 else

arch/riscv/lib/Makefile

@@ -2,5 +2,6 @@ lib-y	+= delay.o
 lib-y	+= memcpy.o
 lib-y	+= memset.o
 lib-y	+= uaccess.o
+lib-y	+= tishift.o
 
 lib-$(CONFIG_32BIT) += udivdi3.o

arch/riscv/lib/tishift.S

+/*
+ * Copyright (C) 2018 Free Software Foundation, Inc.
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ */
+  .globl __lshrti3
+__lshrti3:
+  beqz  a2, .L1
+  li    a5,64
+  sub   a5,a5,a2
+  addi  sp,sp,-16
+  sext.w a4,a5
+  blez  a5, .L2
+  sext.w a2,a2
+  sll   a4,a1,a4
+  srl   a0,a0,a2
+  srl   a1,a1,a2
+  or    a0,a0,a4
+  sd    a1,8(sp)
+  sd    a0,0(sp)
+  ld    a0,0(sp)
+  ld    a1,8(sp)
+  addi  sp,sp,16
+  ret
+.L1:
+  ret
+.L2:
+  negw  a4,a4
+  srl   a1,a1,a4
+  sd    a1,0(sp)
+  sd    zero,8(sp)
+  ld    a0,0(sp)
+  ld    a1,8(sp)
+  addi  sp,sp,16
+  ret