Add generic __bswap[ds]i2 implementations

Summary:
In FreeBSD we needed to add generic implementations for `__bswapdi2` and
`__bswapsi2`, since gcc 6.x for mips is emitting calls to these.  See:

https://reviews.freebsd.org/D10838 and https://reviews.freebsd.org/rS318601

The actual mips code generated for these generic C versions is pretty
OK, as can be seen in the (FreeBSD) review.

I checked over gcc sources, and it seems that it can emit these calls on
more architectures, so maybe it's best to simply always add them to the
compiler-rt builtins library.

Reviewers: howard.hinnant, compnerd, petarj, emaste

Reviewed By: compnerd, emaste

Subscribers: mgorny, llvm-commits, arichardson

Differential Revision: https://reviews.llvm.org/D33516

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@303866 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 23 insertions, 0 deletions

diff --git a/lib/builtins/bswapsi2.c b/lib/builtins/bswapsi2.c
new file mode 100644
index 000000000..5d941e69f
--- /dev/null
+++ b/lib/builtins/bswapsi2.c
@@ -0,0 +1,23 @@
+/* ===-- bswapsi2.c - Implement __bswapsi2 ---------------------------------===
+ *
+ *               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 __bswapsi2 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+COMPILER_RT_ABI uint32_t __bswapsi2(uint32_t u) {
+  return (
+      (((u)&0xff000000) >> 24) |
+      (((u)&0x00ff0000) >> 8)  |
+      (((u)&0x0000ff00) << 8)  |
+      (((u)&0x000000ff) << 24));
+}