arc: Use separate predicated patterns for mpyd(u)

arc: Use separate predicated patterns for mpyd(u)

The compiler can match mpyd.eq r0,r1,r0 as a predicated instruction,
which is incorrect. The mpyd(u) instruction takes as input two 32-bit
registers, returning into a double 64-bit even-odd register pair.  For
the predicated case, the ARC instruction decoder expects the
destination register to be the same as the first input register. In
the big-endian case the result is swaped in the destination register
pair, however, the instruction encoding remains the same.  Refurbish
the mpyd(u) patterns to take into account the above observation.

gcc/
2020-12-11  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc.md (mpyd<su_optab>_arcv2hs): New template
	pattern.
	(*pmpyd<su_optab>_arcv2hs): Likewise.
	(*pmpyd<su_optab>_imm_arcv2hs): Likewise.
	(mpyd_arcv2hs): Moved into above template.
	(mpyd_imm_arcv2hs): Moved into above template.
	(mpydu_arcv2hs): Likewise.
	(mpydu_imm_arcv2hs): Likewise.
	(su_optab): New optab prefix for sign/zero-extending operations.

gcc/testsuite/
2020-12-11  Claudiu Zissulescu  <claziss@synopsys.com>

	* gcc.target/arc/pmpyd.c: New test.
	* gcc.target/arc/tmac-1.c: Update.

Signed-off-by: Claudiu Zissulescu <claziss@gmail.com>