[llvm] [AMDGPU] Rework GFX11 VALU Mask Write Hazard (PR #138663)

[Matt Arsenault via llvm-commits]

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@@ -2968,29 +2968,102 @@ bool GCNHazardRecognizer::fixVALUMaskWriteHazard(MachineInstr *MI) {
     return false;
   assert(!ST.hasExtendedWaitCounts());
 
-  if (!ST.isWave64() || !SIInstrInfo::isSALU(*MI))
+  if (!ST.isWave64())
+    return false;
+
+  const bool IsSALU = SIInstrInfo::isSALU(*MI);
+  const bool IsVALU = SIInstrInfo::isVALU(*MI);
+  if (!IsSALU && !IsVALU)
     return false;
 
   // The hazard sequence is three instructions:
   //   1. VALU reads SGPR as mask
-  //   2. SALU writes SGPR
-  //   3. SALU reads SGPR
+  //   2. VALU/SALU writes SGPR
+  //   3. VALU/SALU reads SGPR
   // The hazard can expire if the distance between 2 and 3 is sufficient.
   // In practice this happens <10% of the time, hence this always assumes
   // the hazard exists if 1 and 2 are present to avoid searching.
 
-  const MachineOperand *SDSTOp = TII.getNamedOperand(*MI, AMDGPU::OpName::sdst);
-  if (!SDSTOp || !SDSTOp->isReg())
-    return false;
+  const SIRegisterInfo *TRI = ST.getRegisterInfo();
+  const MachineRegisterInfo &MRI = MF.getRegInfo();
 
-  const Register HazardReg = SDSTOp->getReg();
-  if (HazardReg == AMDGPU::EXEC ||
-      HazardReg == AMDGPU::EXEC_LO ||
-      HazardReg == AMDGPU::EXEC_HI ||
-      HazardReg == AMDGPU::M0)
+  auto IgnoreableSGPR = [](const Register Reg) {
+    switch (Reg) {
+    case AMDGPU::EXEC:
+    case AMDGPU::EXEC_LO:
+    case AMDGPU::EXEC_HI:
+    case AMDGPU::M0:
+    case AMDGPU::SGPR_NULL:
+    case AMDGPU::SGPR_NULL64:
+    case AMDGPU::SCC:
+      return true;
+    default:
+      return false;
+    }
+  };
+  auto IsVCC = [](const Register Reg) {
+    return Reg == AMDGPU::VCC || Reg == AMDGPU::VCC_LO || Reg == AMDGPU::VCC_HI;
+  };
+
+  struct StateType {
+    SmallSet<Register, 2> HazardSGPRs;
+  };
+
+  SmallVector<const MachineInstr *> WaitInstrs;
+  bool HasSGPRRead = false;
+  StateType InitialState;
+
+  // Look for SGPR write.
+  MachineOperand *HazardDef = nullptr;
+  for (MachineOperand &Op : MI->operands()) {
+    if (!Op.isReg())
+      continue;
+    if (Op.isDef() && HazardDef)
+      continue;
+
+    Register Reg = Op.getReg();
+    if (IgnoreableSGPR(Reg))
+      continue;
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arsenm wrote:

Do explicit uses of exec and m0 really not count as hazards? 

https://github.com/llvm/llvm-project/pull/138663