[ARM] Remove dead instructions before creating VPT block bundles

[dmgreen]

Summary

We remove VPNOT instructions in VPT blocks as we create them, turning them into else predicates. We don't remove the dead instructions until after the block has been created though. Because the VPNOT will have killed the vpr register it used, this makes finalizeBundle add "internal" flags to the vpr uses of any instructions after the VPNOT. These incorrect flags can then confuse what is alive and what is not, leading to machine verifier problems.

This patch removes them earlier instead, before the bundle is finalized so that kill flags remain valid.

[dmgreen]

Ping

[SjoerdMeijer]

Cheers, looks like a good fix to me.

llvm/lib/Target/ARM/MVEVPTBlockPass.cpp

if (MachineInstr *VCMP = findVCMPToFoldIntoVPST(MI, TRI, NewOpcode)) {
       }
 
       VCMP->eraseFromParent();
     } else {
       MIBuilder = BuildMI(Block, MI, DL, TII->get(ARM::MVE_VPST));
       MIBuilder.addImm((uint64_t)BlockMask);
     }
 
+    // Erase all dead instructions (VPNOT's). Do that now so that they do not
+    // mess with the bundle creation.
+    for (MachineInstr *DeadMI : DeadInstructions)
+      DeadMI->eraseFromParent();
+    DeadInstructions.clear();
+
     finalizeBundle(
         Block, MachineBasicBlock::instr_iterator(MIBuilder.getInstr()), MBIter);
 
     Modified = true;
   }
 
-  // Erase all dead instructions
-  for (MachineInstr *DeadMI : DeadInstructions) {
-    if (DeadMI->isInsideBundle())
-      DeadMI->eraseFromBundle();
-    else
-      DeadMI->eraseFromParent();
-  }
-
   return Modified;
 }
 
 bool MVEVPTBlock::runOnMachineFunction(MachineFunction &Fn) {
   const ARMSubtarget &STI =
       static_cast<const ARMSubtarget &>(Fn.getSubtarget());
 
   if (!STI.isThumb2() || !STI.hasMVEIntegerOps())

llvm/test/CodeGen/Thumb2/mve-vpt-3-blocks-kill-vpr.mir

 body:             |
   bb.0.entry:
     liveins: $q0, $q1, $q2, $r0
 
     ; CHECK-LABEL: name: vpt_3_blocks_kill_vpr
     ; CHECK: liveins: $q0, $q1, $q2, $r0
     ; CHECK: $vpr = VMSR_P0 killed $r0, 14 /* CC::al */, $noreg
     ; CHECK: $q3 = MVE_VORR $q0, $q0, 0, $noreg, undef $q3
-    ; CHECK: BUNDLE implicit-def dead $q3, implicit-def $d6, implicit-def $s12, implicit-def $s13, implicit-def $d7, implicit-def $s14, implicit-def $s15, implicit-def $vpr, implicit-def $q1, implicit-def $d2, implicit-def $s4, implicit-def $s5, implicit-def $d3, implicit-def $s6, implicit-def $s7, implicit killed $vpr, implicit killed $q1, implicit $q2, implicit killed $q3 {
+    ; CHECK: BUNDLE implicit-def dead $q3, implicit-def $d6, implicit-def $s12, implicit-def $s13, implicit-def $d7, implicit-def $s14, implicit-def $s15, implicit-def $q1, implicit-def $d2, implicit-def $s4, implicit-def $s5, implicit-def $d3, implicit-def $s6, implicit-def $s7, implicit $vpr, implicit killed $q1, implicit $q2, implicit killed $q3 {
     ; CHECK:   MVE_VPST 12, implicit $vpr
     ; CHECK:   renamable $q3 = nnan ninf nsz MVE_VMINNMf32 killed renamable $q1, renamable $q2, 1, renamable $vpr, killed renamable $q3
-    ; CHECK:   renamable $q1 = nnan ninf nsz MVE_VMINNMf32 internal killed renamable $q3, internal renamable $q3, 2, internal renamable $vpr, undef renamable $q1
+    ; CHECK:   renamable $q1 = nnan ninf nsz MVE_VMINNMf32 internal killed renamable $q3, internal renamable $q3, 2, renamable $vpr, undef renamable $q1
     ; CHECK: }
     ; CHECK: $q3 = MVE_VORR $q0, $q0, 0, $noreg, undef $q3
     ; CHECK: BUNDLE implicit-def dead $q3, implicit-def $d6, implicit-def $s12, implicit-def $s13, implicit-def $d7, implicit-def $s14, implicit-def $s15, implicit-def $q0, implicit-def $d0, implicit-def $s0, implicit-def $s1, implicit-def $d1, implicit-def $s2, implicit-def $s3, implicit killed $vpr, implicit killed $q1, implicit killed $q2, implicit killed $q3, implicit killed $q0 {
     ; CHECK:   MVE_VPST 4, implicit $vpr
     ; CHECK:   renamable $q3 = nnan ninf nsz MVE_VMINNMf32 killed renamable $q1, renamable $q2, 1, renamable $vpr, killed renamable $q3
     ; CHECK:   renamable $q0 = nnan ninf nsz MVE_VMINNMf32 internal killed renamable $q3, killed renamable $q2, 1, killed renamable $vpr, killed renamable $q0
     ; CHECK: }
     ; CHECK: tBX_RET 14 /* CC::al */, $noreg, implicit $q0