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


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@299675 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 31 insertions, 0 deletions

diff --git a/lib/builtins/CMakeLists.txt b/lib/builtins/CMakeLists.txt
index 3f648dcb3..28901034e 100644
--- a/lib/builtins/CMakeLists.txt
+++ b/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
diff --git a/lib/builtins/README.txt b/lib/builtins/README.txt
index ad36e4e52..b3d083614 100644
--- a/lib/builtins/README.txt
+++ b/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
 
diff --git a/lib/builtins/ffssi2.c b/lib/builtins/ffssi2.c
new file mode 100644
index 000000000..e5180eff5
--- /dev/null
+++ b/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;
+}