[llvm] [CodeGen] Refactor DeadMIElim isDead and GISel isTriviallyDead (PR #105956)

[Matt Arsenault via llvm-commits]

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@@ -1323,6 +1323,26 @@ bool MachineInstr::isSafeToMove(bool &SawStore) const {
   return true;
 }
 
+bool MachineInstr::wouldBeTriviallyDead() const {
+  // Don't delete frame allocation labels.
+  // FIXME: Why is LOCAL_ESCAPE not considered in MachineInstr::isLabel?
+  if (getOpcode() == TargetOpcode::LOCAL_ESCAPE)
+    return false;
+
+  // LIFETIME markers should be preserved.
+  // FIXME: Why are LIFETIME markers not considered in MachineInstr::isPosition?
+  if (isLifetimeMarker())
+    return false;
+
+  // If we can move an instruction, we can remove it.  Otherwise, it has
+  // a side-effect of some sort.
+  bool SawStore = false;
+  if (!isSafeToMove(SawStore) && !isPHI())
+    return false;
+
+  return true;
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arsenm wrote:

fold to return of bool expression? 

https://github.com/llvm/llvm-project/pull/105956