[PATCH][AArch64] Leveraging the use of STP instruction for vec_duplicate

The backend pattern for storing a pair of identical values in 32 and 64-bit modes with the machine instruction STP was missing, and multiple instructions were needed to reproduce this behavior as a result of failed RTL pattern match in combine pass. For the test case : typedef long long v2di _

[PATCH][AArch64] Leveraging the use of STP instruction for vec_duplicate

Dear GCC community, The backend pattern for storing a pair of identical values in 32 and 64-bit modes with the machine instruction STP was missing, and multiple instructions were needed to reproduce this behavior as a result of failed RTL pattern match in combine pass. For the test case : ty