If, in between the splat and the load (which does an implicit splat), there is
a read of the splat register, then that register must have another earlier
definition. In that case, we can't replace the load's destination register with
the splat's destination register.
Unfortunately, I don't have a small or non-fragile test case.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268152 91177308-0d34-0410-b5e6-96231b3b80d8
Chapter 3 of the QPX manual states that, "Scalar floating-point load
instructions, defined in the Power ISA, cause a replication of the source data
across all elements of the target register." Thus, if we have a load followed
by a QPX splat (from the first lane), the splat is redundant. This adds a late
MI-level pass to remove the redundant splats in some of these cases
(specifically when both occur in the same basic block).
This optimization is scheduled just prior to post-RA scheduling. It can't happen
before anything that might replace the load with some already-computed quantity
(i.e. store-to-load forwarding).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265047 91177308-0d34-0410-b5e6-96231b3b80d8
