[Mlir-commits] [mlir] [mlir][Parser] Fix use-after-free when parsing invalid reference to nested definition (PR #127778)

[Will Dietz]

https://github.com/dtzSiFive approved this pull request.

LGTM! Small suggestion while reviewing.

This looks to fix crash with input IR from #107121, which now produces:
```
issue-107121.mlir:1:1: error: operation's operand is unlinked
scf.if %true {
^
issue-107121.mlir:1:1: note: see current operation:
"scf.if"(<<UNKNOWN SSA VALUE>>) ({
  %0 = "arith.constant"() <{value = true}> : () -> i1
  "scf.yield"() : () -> ()
}, {
}) : (i1) -> ()
```

Although maybe this still not ideal, it at least no longer crashes.

(probably scf.if's parser should be altered similarly? I can take a look :+1:)

https://github.com/llvm/llvm-project/pull/127778