[PATCH] D78586: [MachineVerifier] Add more checks for registers in live-in lists.

[Zhang Kang via Phabricator via llvm-commits]

ZhangKang added a comment.

I have seen below pattern:

      dead renamable $x5 = MULHDU_rec killed renamable $x5, renamable $x4, implicit-def $cr0
  ...
      BLR8 implicit $lr8, implicit $rm, implicit $x3, implicit $x4, implicit $x5

BLR8 uses `implicit $x5`， but the  ` $x5` is a dead reg. After using this patch, the MachineVerifier still don't give any error. 
Above error is caused by the pass `virtregrewriter`. You can use below command to get above pattern:

  llc llvm/llvm/test/CodeGen/PowerPC/umulo-128-legalisation-lowering.ll -mtriple=powerpc64-unknown-linux-gnu -stop-after=virtregrewriter -o stop-after.mir -verify-machineinstrs

Maybe we can more strict to check above case and give an error.



================
Comment at: llvm/lib/CodeGen/MachineVerifier.cpp:2451
+        // We don't track liveness for reserved registers.
+        if (isReserved(LiveInReg))
+          continue;
----------------
In the file `lib/CodeGen/LivePhysRegs.cpp`:
```
 57 /// Add uses to the set.
 58 void LivePhysRegs::addUses(const MachineInstr &MI) {
 59   for (const MachineOperand &MOP : phys_regs_and_masks(MI)) {
 60     if (!MOP.isReg() || !MOP.readsReg())
 61       continue;
 62     addReg(MOP.getReg());
 63   }
 64 }
 65
 66 /// Simulates liveness when stepping backwards over an instruction(bundle):
 67 /// Remove Defs, add uses. This is the recommended way of calculating liveness.
 68 void LivePhysRegs::stepBackward(const MachineInstr &MI) {
 69   // Remove defined registers and regmask kills from the set.
 70   removeDefs(MI);
 71
 72   // Add uses to the set.
 73   addUses(MI);
 74 }
```

When we calculate the liveness by using the method `stepBackend`, we have added the reserved registers into the liveness in `addUses`, but here, we don't track the reserved registers. Are the `addUses` and the verification correct?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D78586/new/

https://reviews.llvm.org/D78586