The following patch provides builtin support for byte swapping and bit counting.
On suitable hardware, these generate the x86 popcount instructions, as also
generated by the SUN HotSpot JIT/JVM for these method calls.

java.lang.Integer.bitCount -> __builtin_popcount
java.lang.Long.bitCount -> __builtin_popcountl

java.lang.Short.reverseBytes -> __builtin_bswap16
java.lang.Integer.reverseBytes -> __builtin_bswap32
java.lang.Long.reverseBytes -> __builtin_bswap64

New test cases have been added to libjava to double check nothing breaks.
Whist I was there I noticed that the math builtins (many of which I added support for
back in 2003/2004) weren't marked as ECF_LEAF, indicating that they don't/can't
invoke any user specified functions.   This has also been fixed in the patch below.

The following patch has been tested on x86_64-pc-linux-gnu with a full make bootstrap
and make check with no new failures/regressions.

Ok for stage1 once it reopens?

Cheers,

Roger
--
Roger Sayle, Ph.D.
CEO and founder
NextMove Software Limited
Registered in England No. 07588305
Registered Office: Innovation Centre (Unit 23), Cambridge Science Park, Cambridge CB4 0EY

2016-02-21  Roger Sayle  <roger@nextmovesoftware.com>

gcc/java:
	* builtins.c (java_builtins): Use popcount* and bswap* builtins to
	implement bitCount() and reverseBytes() methods in java.lang.Integer
	and friends.
	(initialize_builtins): Annotate math builtins with ECF_LEAF.  Call
	define_builtin for the new popcount* and bswap* builtins.

libjava:
	* testsuite/libjava.lang/BuiltinBitCount.java: New test case.
	* testsuite/libjava.lang/BuiltinReverseBytes.java: Likewise.