R600: Use legacy (0 * anything = 0) MUL instructions for pow intrinsics
Fixes wrong lighting in some corner cases with r600g and radeonsi, e.g.
manifested by failure of two piglit/glean tests and intermittent black
patches in many apps.
Tested on SI and RS880.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=62012 [radeonsi]
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=58150 [r600g]
NOTE: This is a candidate for the Mesa stable branch.
Reviewed-by: Christian König <christian.koenig@amd.com>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177730
91177308-0d34-0410-b5e6-
96231b3b80d8