[ARM][MVE] Remove kill flags when reusing VPR register. (#86300)

The vpr register may no longer be killed where it was, so we should be
removing the kill flags.

Author: davemgreen

llvm/lib/Target/ARM/MVETPAndVPTOptimisationsPass.cpp

@@ -958,6 +958,7 @@ bool MVETPAndVPTOptimisations::ReplaceConstByVPNOTs(MachineBasicBlock &MBB,
 
     unsigned NotImm = ~Imm & 0xffff;
     if (LastVPTReg != 0 && LastVPTReg != VPR && LastVPTImm == Imm) {
+      MRI->clearKillFlags(LastVPTReg);
       Instr.getOperand(PIdx + 1).setReg(LastVPTReg);
       if (MRI->use_empty(VPR)) {
         DeadInstructions.insert(Copy);

llvm/test/CodeGen/Thumb2/mve-vpt-optimisations.mir

@@ -1,5 +1,5 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
-# RUN: llc -mtriple=thumbv8.1m.main-none-none-eabi -mattr=+armv8.1-m.main,+hwdiv,+mve.fp,+ras,+thumb-mode -run-pass arm-mve-vpt-opts %s -o - | FileCheck %s
+# RUN: llc -mtriple=thumbv8.1m.main-none-none-eabi -mattr=+armv8.1-m.main,+hwdiv,+mve.fp,+ras,+thumb-mode -run-pass arm-mve-vpt-opts -verify-machineinstrs %s -o - | FileCheck %s
 
 ---
 name:            vcmp_with_opposite_cond
@@ -1021,3 +1021,26 @@ body:             |
     %16:mqpr = MVE_VORR %15, %15, 1, %10, $noreg, undef %16
     %17:mqpr = MVE_VORR %16, %16, 1, %11, $noreg, undef %17
 ...
+---
+name:            reuse_kill_flags
+alignment:       4
+body:             |
+  bb.0:
+    ; CHECK-LABEL: name: reuse_kill_flags
+    ; CHECK: [[t2MOVi:%[0-9]+]]:tgpreven = t2MOVi 0, 14 /* CC::al */, $noreg, $noreg
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:vccr = COPY [[t2MOVi]]
+    ; CHECK-NEXT: [[DEF:%[0-9]+]]:mqpr = IMPLICIT_DEF
+    ; CHECK-NEXT: [[MVE_VORR:%[0-9]+]]:mqpr = MVE_VORR [[DEF]], [[DEF]], 1, [[COPY]], $noreg, undef [[MVE_VORR]]
+    ; CHECK-NEXT: [[DEF1:%[0-9]+]]:mqpr = IMPLICIT_DEF
+    ; CHECK-NEXT: [[MVE_VORR1:%[0-9]+]]:mqpr = MVE_VORR [[DEF1]], [[DEF1]], 1, killed [[COPY]], $noreg, undef [[MVE_VORR1]]
+    ; CHECK-NEXT: tBX_RET 14 /* CC::al */, $noreg, implicit [[DEF1]]
+    %0:tgpreven = t2MOVi 0, 14, $noreg, $noreg
+    %1:vccr = COPY %0:tgpreven
+    %2:mqpr = IMPLICIT_DEF
+    %3:mqpr = MVE_VORR %2:mqpr, %2:mqpr, 1, killed %1, $noreg, undef %3
+    %4:vccr = COPY %0:tgpreven
+    %5:mqpr = IMPLICIT_DEF
+    %6:mqpr = MVE_VORR %5:mqpr, %5:mqpr, 1, killed %4, $noreg, undef %6
+    tBX_RET 14 /* CC::al */, $noreg, implicit %5:mqpr
+
+...