[llvm] [MachineLateInstrsCleanup] Handle multiple kills for a preceding definition. (PR #119132)

[Jonas Paulsson via llvm-commits]

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@@ -113,33 +113,39 @@ bool MachineLateInstrsCleanup::runOnMachineFunction(MachineFunction &MF) {
 // definition.
 void MachineLateInstrsCleanup::clearKillsForDef(Register Reg,
                                                 MachineBasicBlock *MBB,
-                                                BitVector &VisitedPreds) {
+                                                BitVector &VisitedPreds,
+                                                MachineInstr *ToRemoveMI) {
   VisitedPreds.set(MBB->getNumber());
 
-  // Kill flag in MBB
-  if (MachineInstr *KillMI = RegKills[MBB->getNumber()].lookup(Reg)) {
-    KillMI->clearRegisterKills(Reg, TRI);
-    return;
-  }
+  // Clear kill flag(s) in MBB, that have been seen after the preceding
+  // definition. If Reg or one of its subregs was killed, it would actually
+  // be ok to stop after removing that (and any other) kill-flag, but it
+  // doesn't seem noticeably faster while it would be a bit more complicated.
+  Reg2MIVecMap &MBBKills = RegKills[MBB->getNumber()];
+  if (auto Kills = MBBKills.find(Reg); Kills != MBBKills.end())
+    for (auto *KillMI : Kills->second)
+      KillMI->clearRegisterKills(Reg, TRI);
 
-  // Def in MBB (missing kill flag)
-  if (MachineInstr *DefMI = RegDefs[MBB->getNumber()].lookup(Reg))
-    if (DefMI->getParent() == MBB)
-      return;
+  // Definition in current MBB: done.
+  Reg2MIMap &MBBDefs = RegDefs[MBB->getNumber()];
+  MachineInstr *DefMI = MBBDefs[Reg];
+  assert(DefMI->isIdenticalTo(*ToRemoveMI) && "Previous def not identical?");
----------------
JonPsson1 wrote:

Yeah, I guess maybe that assertion could be a separate patch. The whole idea of the pass is to remove a redundant definition because there is an identical dominating one. Given the CFG traversal involved here (DefMI may be in a predecessor), it seems fair to do the assertion. Should I remove it from this patch now, you think?

https://github.com/llvm/llvm-project/pull/119132