[PATCH] [PowerPC] Add Power8 Instruction Scheduling Tablegen

[Will Schmidt]

I've been discussing a few related details with Pat Haugen on the side. I'll make a few updates and repost early in the coming week.

Notably, I'm missing a pair of LU units in this diff. 

The gist of the clarification I got from Pat regarding the instruction dispatching is.. P7 has a 6 instruction dispatch group, with 8 instructions per cycle. P8 has an 8 instruction dispatch group and can issue 10 instructions per cycle.

================
Comment at: lib/Target/PowerPC/PPCScheduleP8.td:359
@@ +358,3 @@
+def P8Model : SchedMachineModel {
+  let IssueWidth = 8;  // up to 8 instructions dispatched per cycle.
+                       // up to six non-branch instructions.
----------------
hfinkel wrote:
> If your comments capture the entire picture, then this should be 6, not 8. I think that, the real question, however, is not the instructions in each dispatch group going in, but how many (non-branch) instructions can be issued per cycle to the various pipelines.
> 
> On the P7, this is 8 (two of which are branches, so 6 regular instructions), even though we can have only 4 per dispatch group. That;s why I put 6 in this field for the P7.
I've been discussing a few related details with Pat Haugen on the side.     I'll make a few updates and repost early in the coming week. 

Notably, I'm missing a pair of LU units in this diff.  

The gist of the clarification I got from Pat regarding the instruction dispatching is..   P7 has a 6 instruction dispatch group, with 8 instructions per cycle.  P8 has an 8 instruction dispatch group and can issue 10 instructions per cycle.

http://reviews.llvm.org/D6358