[llvm] [AMDGPU] Fix GCNUpwardRPTracker. (WIP) (PR #71186)

[Jay Foad via llvm-commits]

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@@ -180,6 +190,13 @@ class GCNDownwardRPTracker : public GCNRPTracker {
 
   MachineBasicBlock::const_iterator getNext() const { return NextMI; }
 
+  // Return MaxPressure and clear it.
+  decltype(MaxPressure) moveMaxPressure() {
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jayfoad wrote:

Why use decltype? It's longer than GCNRegPressure.

https://github.com/llvm/llvm-project/pull/71186