rs6000: Do not allow combining of multiple assemble quads [PR103548]

rs6000: Do not allow combining of multiple assemble quads [PR103548]

The compiler will gladly CSE the result of two __builtin_mma_build_acc
calls with the same four vector arguments, leading to illegal MMA
code being generated.  The fix here is to make the mma_assemble_acc
pattern use a unspec_volatile to stop the CSE from happening.

2021-12-14  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	PR target/103548
	* config/rs6000/mma.md (UNSPEC_MMA_ASSEMBLE): Rename unspec from this...
	(UNSPEC_VSX_ASSEMBLE): ...to this.
	(UNSPECV_MMA_ASSEMBLE): New unspecv.
	(vsx_assemble_pair): Use UNSPEC_VSX_ASSEMBLE.
	(*vsx_assemble_pair): Likewise.
	(mma_assemble_acc): Use UNSPECV_MMA_ASSEMBLE.
	(*mma_assemble_acc): Likewise.
	* config/rs6000/rs6000.c (rs6000_split_multireg_move): Handle
	UNSPEC_VOLATILE.  Use UNSPEC_VSX_ASSEMBLE and UNSPECV_MMA_ASSEMBLE.

gcc/testsuite/
	PR target/103548
	* gcc.target/powerpc/mma-builtin-10-pair.c: New test.
	* gcc.target/powerpc/mma-builtin-10-quad.c: New test.