[llvm-branch-commits] [llvm] [2/3][AMDGPU] Physical register tracking in GCN trackers. (PR #184275)

[Matt Arsenault via llvm-branch-commits]

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@@ -320,12 +325,72 @@ class GCNRPTracker {
 
 protected:
   const LiveIntervals &LIS;
+
   LiveRegSet VirtLiveRegs;
+
+  // Physical register liveness: Units provides O(1) unit-level alias checks,
+  // Regs tracks which register names contributed to pressure for cheap
+  // reconstruction. Both must be kept in sync.
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arsenm wrote:

> Since this kind of overlap should be rare in practice, to keep things efficient, I am leaning towards not making this change. Instead, I will document this potential issue.

The liveness needs to be accurately modeled, at any cost. The scheduler cannot afford to oversubscribe the allocator 

https://github.com/llvm/llvm-project/pull/184275