Add __ffssi2 implementation to compiler-rt builtins

Summary:
During MIPS implementation work for FreeBSD, John Baldwin (jhb@FreeBSD.org)
found that gcc 6.x emits calls to __ffssi2() when compiling libc and some
userland programs in the base system.

Add it to compiler-rt's builtins, based off of the existing __ffsdi2()
implementation.  Also update the CMake files and add a test case.

Reviewers: howard.hinnant, weimingz, rengolin, compnerd

Reviewed By: weimingz

Subscribers: dberris, mgorny, llvm-commits, emaste

Differential Revision: https://reviews.llvm.org/D31721

llvm-svn: 299675

compiler-rt/lib/builtins/CMakeLists.txt

@@ -71,6 +71,7 @@ set(GENERIC_SOURCES
   extendsfdf2.c
   extendhfsf2.c
   ffsdi2.c
+  ffssi2.c
   ffsti2.c
   fixdfdi.c
   fixdfsi.c

compiler-rt/lib/builtins/README.txt

@@ -45,6 +45,7 @@ si_int __ctzsi2(si_int a);  // count trailing zeros
 si_int __ctzdi2(di_int a);  // count trailing zeros
 si_int __ctzti2(ti_int a);  // count trailing zeros
 
+si_int __ffssi2(si_int a);  // find least significant 1 bit
 si_int __ffsdi2(di_int a);  // find least significant 1 bit
 si_int __ffsti2(ti_int a);  // find least significant 1 bit
 

compiler-rt/lib/builtins/ffssi2.c

@@ -0,0 +1,29 @@
+/* ===-- ffssi2.c - Implement __ffssi2 -------------------------------------===
+ *
+ *                     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 __ffssi2 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+/* Returns: the index of the least significant 1-bit in a, or
+ * the value zero if a is zero. The least significant bit is index one.
+ */
+
+COMPILER_RT_ABI si_int
+__ffssi2(si_int a)
+{
+    if (a == 0)
+    {
+        return 0;
+    }
+    return __builtin_ctz(a) + 1;
+}

compiler-rt/test/builtins/Unit/ffssi2_test.c

@@ -0,0 +1,57 @@
+// RUN: %clang_builtins %s %librt -o %t && %run %t
+//===-- ffssi2_test.c - Test __ffssi2 -------------------------------------===//
+//
+//                     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 tests __ffssi2 for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "int_lib.h"
+#include <stdio.h>
+
+// Returns: the index of the least significant 1-bit in a, or
+// the value zero if a is zero. The least significant bit is index one.
+
+COMPILER_RT_ABI si_int __ffssi2(si_int a);
+
+int test__ffssi2(si_int a, si_int expected)
+{
+    si_int x = __ffssi2(a);
+    if (x != expected)
+        printf("error in __ffssi2(0x%X) = %d, expected %d\n", a, x, expected);
+    return x != expected;
+}
+
+int main()
+{
+    if (test__ffssi2(0x00000000, 0))
+        return 1;
+    if (test__ffssi2(0x00000001, 1))
+        return 1;
+    if (test__ffssi2(0x00000002, 2))
+        return 1;
+    if (test__ffssi2(0x00000003, 1))
+        return 1;
+    if (test__ffssi2(0x00000004, 3))
+        return 1;
+    if (test__ffssi2(0x00000005, 1))
+        return 1;
+    if (test__ffssi2(0x0000000A, 2))
+        return 1;
+    if (test__ffssi2(0x10000000, 29))
+        return 1;
+    if (test__ffssi2(0x20000000, 30))
+        return 1;
+    if (test__ffssi2(0x60000000, 30))
+        return 1;
+    if (test__ffssi2(0x80000000u, 32))
+        return 1;
+
+   return 0;
+}