[Bug target/91481] POWER9 "DARN" RNG intrinsic produces repeated output

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91481

--- Comment #7 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Author: segher
Date: Fri Aug 23 22:19:40 2019
New Revision: 274889

URL: https://gcc.gnu.org/viewcvs?rev=274889&root=gcc&view=rev
Log:
rs6000: New darn testcase (PR91481)

We used to implement darn with unspecs, not unspec_volatiles, which
means two darn instructions could be CSEd together.

This testcase tests it by adding together four random numbers.  If all
is well that means we get four darn instructions, because such a small
loop is unrolled fine at -O2 already.  If things go bad, combine will
combine it all to one darn and a shift left by two.


gcc/testsuite/
        PR target/91481
        * gcc.target/powerpc/darn-3.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.target/powerpc/darn-3.c
Modified:
    trunk/gcc/testsuite/ChangeLog