[llvm] [AMDGPUFix GCUpwardRPTracker. (PR #74328)

[Valery Pykhtin via llvm-commits]

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@@ -274,48 +269,48 @@ void GCNUpwardRPTracker::recede(const MachineInstr &MI) {
   if (MI.isDebugInstr())
     return;
 
-  auto DecrementDef = [this](const MachineOperand &MO) {
+  // Kill all defs.
+  GCNRegPressure DefPressure, ECDefPressure;
+  for (const MachineOperand &MO : MI.all_defs()) {
+    if (!MO.getReg().isVirtual())
+      continue;
+
     Register Reg = MO.getReg();
+    LaneBitmask DefMask = getDefRegMask(MO, *MRI);
+
+    // Treat a def as fully live at the moment of definition: keep a record.
+    (MO.isEarlyClobber() ? &ECDefPressure : &DefPressure)
+        ->inc(Reg, LaneBitmask::getNone(), DefMask, *MRI);
+
     auto I = LiveRegs.find(Reg);
     if (I == LiveRegs.end())
-      return;
+      continue;
 
     LaneBitmask &LiveMask = I->second;
     LaneBitmask PrevMask = LiveMask;
-    LiveMask &= ~getDefRegMask(MO, *MRI);
+    LiveMask &= ~DefMask;
     CurPressure.inc(Reg, PrevMask, LiveMask, *MRI);
     if (LiveMask.none())
       LiveRegs.erase(I);
-  };
-
-  // Decrement non-early-clobber defs.
-  SmallVector<const MachineOperand *, 2> EarlyClobberDefs;
-  for (const MachineOperand &MO : MI.all_defs()) {
-    if (!MO.getReg().isVirtual())
-      continue;
-    if (!MO.isEarlyClobber())
-      DecrementDef(MO);
-    else
-      EarlyClobberDefs.push_back(&MO);
   }
 
-  // Increment uses.
+  // Update MaxPressure with defs pressure.
+  MaxPressure = max(CurPressure + DefPressure + ECDefPressure, MaxPressure);
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vpykhtin wrote:

It probably worth to add _ECDefPressure_ conditionally as early-clobbers are very rare (if any).

https://github.com/llvm/llvm-project/pull/74328