[AArch64][SVE] Remove unnecessary PTRUEs from integer arithmetic

[AArch64][SVE] Remove unnecessary PTRUEs from integer arithmetic

When using the unpredicated immediate forms of MUL, LSL, LSR and ASR,
the rtl patterns would still have the predicate operand we created for
the other forms.  This patch splits the patterns after reload in order
to get rid of the predicate, like we already do for WHILE.

2018-12-07  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64-sve.md (*mul<mode>3, *v<optab><mode>3):
	Split the patterns after reload if we don't need the predicate
	operand.
	(*post_ra_mul<mode>3, *post_ra_v<optab><mode>3): New patterns.

gcc/testsuite/
	* gcc.target/aarch64/sve/pred_elim_2.c: New test.

From-SVN: r266892