[PATCH] D60419: Avoid removing physreg uses in MachineDCE with LIS present

[Stanislav Mekhanoshin via Phabricator via llvm-commits]

rampitec created this revision.
rampitec added a reviewer: bjope.

One of OOT targets hits "Live segment doesn't end at a valid instruction"
error if physreg use is removed. I do not have a reproducer for that or
access to the target, but that seems to be reasonable to avoid removing
dead phys reg uses for the same reason as dead defs.


https://reviews.llvm.org/D60419

Files:
  lib/CodeGen/DeadMachineInstructionElim.cpp


Index: lib/CodeGen/DeadMachineInstructionElim.cpp
===================================================================
--- lib/CodeGen/DeadMachineInstructionElim.cpp
+++ lib/CodeGen/DeadMachineInstructionElim.cpp
@@ -77,24 +77,32 @@
   // Examine each operand.
   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = MI->getOperand(i);
-    if (MO.isReg() && MO.isDef()) {
-      unsigned Reg = MO.getReg();
-      if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
-        // Don't delete live physreg defs, or any reserved register defs.
-        // Do not remove physreg defs if we have LIS as we may be unable
-        // to accurately recompute its liveness.
-        if (LivePhysRegs.test(Reg) || MRI->isReserved(Reg) || LIS)
+    if (!MO.isReg())
+      continue;
+
+    unsigned Reg = MO.getReg();
+    // Do not remove physreg defs or uses if we have LIS as we may be unable
+    // to accurately recompute its liveness.
+    if (LIS && TargetRegisterInfo::isPhysicalRegister(Reg) &&
+        MRI->isAllocatable(Reg))
+      return false;
+
+    if (!MO.isDef())
+      continue;
+
+    if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
+      // Don't delete live physreg defs, or any reserved register defs.
+      if (LivePhysRegs.test(Reg) || MRI->isReserved(Reg) || LIS)
+        return false;
+    } else {
+      // An instruction can also use its def in case if it is a tied operand.
+      // TODO: Technically we can also remove it if def dominates the use.
+      //       This can happen when two instructions define different subregs
+      //       of the same register.
+      for (const MachineInstr &Use : MRI->use_nodbg_instructions(Reg)) {
+        if (&Use != MI)
+          // This def has a non-debug use. Don't delete the instruction!
           return false;
-      } else {
-        // An instruction can also use its def in case if it is a tied operand.
-        // TODO: Technically we can also remove it if def dominates the use.
-        //       This can happen when two instructions define different subregs
-        //       of the same register.
-        for (const MachineInstr &Use : MRI->use_nodbg_instructions(Reg)) {
-          if (&Use != MI)
-            // This def has a non-debug use. Don't delete the instruction!
-            return false;
-        }
       }
     }
   }


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