[PATCH] nvptx: Add support for PTX highpart multiplications (HI/SI)

[PATCH] nvptx: Add support for PTX highpart multiplications (HI/SI)

This patch adds support for signed and unsigned, HImode and SImode highpart
multiplications to the nvptx backend.

This patch has been tested on nvptx-none hosted on x86_64-pc-linux-gnu
with a "make" and "make -k check" with no new failures with the
above patch.

2020-08-04  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog:

	* config/nvptx/nvptx.md (smulhi3_highpart, smulsi3_highpart)
	(umulhi3_highpart, umulsi3_highpart): New instructions.

gcc/testsuite/ChangeLog:

	* gcc.target/nvptx/mul-hi.c: New test.
	* gcc.target/nvptx/umul-hi.c: New test.