[LiveRangeEdit] Remove any MemoryOperand on MI when converting it to KILL. (#114407)

When LiveRangeEdit::eliminateDeadDef() converts an MI to a KILL instruction,
it should also call dropMemRefs() in order to erase any MachineMemOperand
present.

This was discovered in testing as the MachineVerifier does not accept an MMO
without the corresponding MI mayLoad/mayStore flag, which the KILL opcode
lacks.

Author: JonPsson1

llvm/lib/CodeGen/LiveRangeEdit.cpp

@@ -385,6 +385,7 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
         continue;
       MI->removeOperand(i-1);
     }
+    MI->dropMemRefs(*MI->getMF());
     LLVM_DEBUG(dbgs() << "Converted physregs to:\t" << *MI);
   } else {
     // If the dest of MI is an original reg and MI is reMaterializable,

llvm/test/CodeGen/SystemZ/liverangeedit-kill-memop.mir

@@ -0,0 +1,29 @@
+# RUN: llc -o /dev/null %s -mtriple=s390x-linux-gnu -mcpu=z16 \
+# RUN:   -verify-machineinstrs -run-pass=register-coalescer
+
+# The LOCMux below produces a dead definition and will be turned into
+# a KILL instruction (by LiveRangeEdit::eliminateDeadDef()). When this
+# happens, the MemoryOperand must also be removed as this is required
+# by the machine verifier.
+
+---
+name:            fun
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $r2d
+  
+    %3:addr64bit = COPY killed $r2d
+  
+  bb.1:
+    %5:grx32bit = LMux killed %3, 0, $noreg :: (load (s32))
+    CHIMux killed %5, 0, implicit-def $cc
+    %7:grx32bit = LHIMux 0
+    %1:grx32bit = COPY killed %7
+    %1:grx32bit = LOCMux %1, undef %8:addr64bit, 0, 14, 6, implicit killed $cc :: (load (s32))
+    dead %0:grx32bit = COPY killed %1
+  
+  bb.2:
+    J %bb.2
+
+...