[llvm] [SandboxIR][Tracker] Track eraseFromParent() (PR #99431)

[Arthur Eubanks via llvm-commits]

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@@ -99,6 +100,46 @@ class UseSet : public IRChangeBase {
 #endif
 };
 
+class EraseFromParent : public IRChangeBase {
+  /// Contains all the data we need to restore an "erased" (i.e., detached)
+  /// instruction: the instruction itself and the operands data.
+  struct InstrData {
+    /// The operand and the corresponding operand number.
+    struct OpData {
+      llvm::Value *Op;
+      unsigned OpNum;
+    };
+    /// The operands that got dropped.
+    SmallVector<OpData> OpDataVec;
+    /// The instruction that got "erased".
+    llvm::Instruction *LLVMI;
+  };
+  /// The instruction data is in reverse program order, which helps create the
+  /// original program order during revert().
+  SmallVector<InstrData> InstrData;
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aeubanks wrote:

if we add a test extension it should be pretty clear that it's not for users. that would also be a nice way to show how to write an extension that doesn't contain all the vectorization complexity.

but I'm ok with adding a TODO to test multi-instructions and filling that in in a separate PR that adds a test extension

https://github.com/llvm/llvm-project/pull/99431