[llvm] [AMDGPU] RFC: Add and optionally use GCNIterativeRPTrackers (PR #88797)

[Jeffrey Byrnes via llvm-commits]

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@@ -343,6 +343,48 @@ void GCNRPTracker::reset(const MachineInstr &MI,
   MaxPressure = CurPressure = getRegPressure(*MRI, LiveRegs);
 }
 
+DenseMap<int, GCNRPTracker::LiveRegSet>
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jrbyrnes wrote:

> I'm not sure what the key is here. I'm also concerned by building maps for liveness info, that's already encoded in the LiveIntervals. 

I've tried to address this in https://github.com/llvm/llvm-project/pull/93089

I've left getLiveRegMap unmodified and used the last MI per region as the key to the liveness info (as is similarly done for BBLiveInMap currently). The result is that we do not introduce any new way of building maps for liveness info. The maps are not strictly necessary, and we could recompute them each time we encounter the same region during scheduling, but they do eliminate redundant calculations.

https://github.com/llvm/llvm-project/pull/88797