[llvm] [MachineCP] Correctly handle register masks and sub-registers (PR #122734)

[Jinsong Ji via llvm-commits]

================
@@ -978,9 +1012,11 @@ void MachineCopyPropagation::ForwardCopyPropagateBlock(MachineBasicBlock &MBB) {
         LLVM_DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
                    MaybeDead->dump());
 
-        // Make sure we invalidate any entries in the copy maps before erasing
-        // the instruction.
-        Tracker.clobberRegister(Reg, *TRI, *TII, UseCopyInstr);
+        // Invalidate all entries in the copy map which are not preserved by
+        // this register mask.
+        for (unsigned RegUnit : TRI->regunits(Reg))
+          if (!PreservedRegUnits.test(RegUnit))
----------------
jsji wrote:

We do, but unfortunately the MIR contains some register class that are downstream only, so we can't provide it now.
The following diff should fix it; however, I don't have reduced MIR available now.

```
diff --git a/llvm/lib/CodeGen/MachineCopyPropagation.cpp b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
index d44b064dcb4b..70dd7d04a153 100644
--- a/llvm/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
@@ -1009,18 +1009,30 @@ void MachineCopyPropagation::ForwardCopyPropagateBlock(MachineBasicBlock &MBB) {
           continue;
         }
 
-        LLVM_DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
-                   MaybeDead->dump());
-
         // Invalidate all entries in the copy map which are not preserved by
         // this register mask.
-        for (unsigned RegUnit : TRI->regunits(Reg))
+        bool MIRefedinCopyInfo = false;
+        for (unsigned RegUnit : TRI->regunits(Reg)) {
           if (!PreservedRegUnits.test(RegUnit))
             Tracker.clobberRegUnit(RegUnit, *TRI, *TII, UseCopyInstr);
+          else {
+            if (MaybeDead == Tracker.findCopyForUnit(RegUnit, *TRI)) {
+              MIRefedinCopyInfo = true;
+            }
+          }
+        }
 
         // erase() will return the next valid iterator pointing to the next
         // element after the erased one.
         DI = MaybeDeadCopies.erase(DI);
+
+        // Preserved by RegMask, DO NOT remove copy
+        if (MIRefedinCopyInfo)
+          continue;
+
+        LLVM_DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
+                   MaybeDead->dump());
+
         MaybeDead->eraseFromParent();
         Changed = true;
         ++NumDeletes;
```

https://github.com/llvm/llvm-project/pull/122734