The instruction addi is usually used to post increase the loop indvar, which looks like this:
label_X:
load x, base(i)
...
y = op x
...
i = addi i, 1
goto label_X
However, for PowerPC, if there are too many vsx instructions that between y = op x and i = addi i, 1,
it will use all the hw resource that block the execution of i = addi, i, 1, which result in the stall
of the load instruction in next iteration. So, a heuristic is added to move the addi as early as possible
to have the load hide the latency of vsx instructions, if other heuristic didn't apply to avoid the starve.
Reviewed By: jji
Differential Revision: https://reviews.llvm.org/D80269
When we are scheduling the load and addi, if all other heuristic didn't take effect,
we will try to schedule the addi before the load, to hide the latency, and avoid the
true dependency added by RA. And this only take effects for Power9.
Differential Revision: https://reviews.llvm.org/D61930
llvm-svn: 361600
This patch lays the groundwork for extending the generic machine scheduler by providing a PPC-specific implementation.
There are no functional changes as this is an incremental patch that simply provides the necessary overrides which just
encapsulate the behavior of the generic scheduler. Subsequent patches will add specific behavior.
Differential Revision: https://reviews.llvm.org/D59284
llvm-svn: 357047
QingShan Zhang