compiler_rt: Import lshrdi3.c file

Imported from the LLVM compiler_rt library on master branch as of
30 Oct 2018 (SVN revision: r345645).

This is to get the __aeabi_llsr() builtin, which is required by a
subsequent patch that uses a logical right shift operator in AArch32.

Change-Id: I9884139a12855a8a87206fb572aaa7dd35582b09
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

lib/compiler-rt/builtins/lshrdi3.c

+/* ===-- lshrdi3.c - Implement __lshrdi3 -----------------------------------===
+ *
+ *                     The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __lshrdi3 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+/* Returns: logical a >> b */
+
+/* Precondition:  0 <= b < bits_in_dword */
+
+COMPILER_RT_ABI di_int
+__lshrdi3(di_int a, si_int b)
+{
+    const int bits_in_word = (int)(sizeof(si_int) * CHAR_BIT);
+    udwords input;
+    udwords result;
+    input.all = a;
+    if (b & bits_in_word)  /* bits_in_word <= b < bits_in_dword */
+    {
+        result.s.high = 0;
+        result.s.low = input.s.high >> (b - bits_in_word);
+    }
+    else  /* 0 <= b < bits_in_word */
+    {
+        if (b == 0)
+            return a;
+        result.s.high  = input.s.high >> b;
+        result.s.low = (input.s.high << (bits_in_word - b)) | (input.s.low >> b);
+    }
+    return result.all;
+}
+
+#if defined(__ARM_EABI__)
+AEABI_RTABI di_int __aeabi_llsr(di_int a, si_int b) COMPILER_RT_ALIAS(__lshrdi3);
+#endif

lib/compiler-rt/compiler-rt.mk

@@ -31,5 +31,6 @@
 ifeq (${ARCH},aarch32)
 COMPILER_RT_SRCS	:=	lib/compiler-rt/builtins/arm/aeabi_uldivmod.S	\
 				lib/compiler-rt/builtins/udivmoddi4.c		\
-				lib/compiler-rt/builtins/ctzdi2.c
+				lib/compiler-rt/builtins/ctzdi2.c		\
+				lib/compiler-rt/builtins/lshrdi3.c
 endif