[llvm] MachineCopyPropagation: Do not remove copies preserved by regmask (PR #125868)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-regalloc

Author: Jinsong Ji (jsji)

<details>
<summary>Changes</summary>

llvm/llvm-project@<!-- -->9e436c2daa44 tries to handle register masks and
sub-registers, it avoids clobbering RegUnit presreved by regmask. But it
then introduces invalid pointer issues.

We delete the copies without invalidate all the use in the CopyInfo, so
we dereferenced invalid pointers in next interation, causing asserts.


---
Full diff: https://github.com/llvm/llvm-project/pull/125868.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/MachineCopyPropagation.cpp (+16-4) 


``````````diff
diff --git a/llvm/lib/CodeGen/MachineCopyPropagation.cpp b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
index 460749a739c763..ba63d4c69d0900 100644
--- a/llvm/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
@@ -1018,18 +1018,30 @@ 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;

``````````

</details>


https://github.com/llvm/llvm-project/pull/125868