[PATCH] D75245: [ARM][RDA] Allow multiple killed users

[Sam Parker via Phabricator via llvm-commits]

samparker created this revision.
samparker added reviewers: SjoerdMeijer, dmgreen.
Herald added subscribers: hiraditya, kristof.beyls.
Herald added a project: LLVM.

In RDA, check against the already decided dead instructions when looking at users. This allows an instruction to be removed if it has multiple users, but they're all dead.
This means that IT instructions can be considered killed once all the itstate using instructions are dead.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D75245

Files:
  llvm/lib/CodeGen/ReachingDefAnalysis.cpp
  llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp


Index: llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
===================================================================
--- llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
+++ llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
@@ -943,11 +943,8 @@
   if (ModifiedITs.empty()) {
     LLVM_DEBUG(dbgs() << "ARM Loops: Will remove iteration count:\n";
                for (auto *MI : Killed)
-                 dbgs() << " - " << *MI;
-               for (auto *MI : DeadITs)
                  dbgs() << " - " << *MI);
     LoLoop.ToRemove.insert(Killed.begin(), Killed.end());
-    LoLoop.ToRemove.insert(DeadITs.begin(), DeadITs.end());
   }
 
   // Collect and remove the users of iteration count.
Index: llvm/lib/CodeGen/ReachingDefAnalysis.cpp
===================================================================
--- llvm/lib/CodeGen/ReachingDefAnalysis.cpp
+++ llvm/lib/CodeGen/ReachingDefAnalysis.cpp
@@ -523,7 +523,7 @@
 void ReachingDefAnalysis::collectLocalKilledOperands(MachineInstr *MI,
                                                      InstSet &Dead) const {
   Dead.insert(MI);
-  auto IsDead = [this](MachineInstr *Def, int PhysReg) {
+  auto IsDead = [this, &Dead](MachineInstr *Def, int PhysReg) {
     unsigned LiveDefs = 0;
     for (auto &MO : Def->operands()) {
       if (!MO.isReg() || !MO.getReg() || MO.isUse())
@@ -537,7 +537,10 @@
 
     SmallPtrSet<MachineInstr*, 4> Uses;
     getGlobalUses(Def, PhysReg, Uses);
-    return Uses.size() == 1;
+    for (auto *Use : Uses)
+      if (!Dead.count(Use))
+        return false;
+    return true;
   };
 
   for (auto &MO : MI->operands()) {


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