[clang] [CIR] Add cir.lifetime.start and cir.lifetime.end Op (PR #199599)

[Henrich Lauko via cfe-commits]

================
@@ -4670,6 +4670,62 @@ def CIR_StackRestoreOp : CIR_Op<"stackrestore"> {
   let assemblyFormat = "$ptr attr-dict `:` qualified(type($ptr))";
 }
 
+//===----------------------------------------------------------------------===//
+// LifetimeStartOp & LifetimeEndOp
+//===----------------------------------------------------------------------===//
+
+def CIR_LifetimeStartOp : CIR_Op<"lifetime.start"> {
+  let summary = "Marks the beginning of an alloca object's live range";
+  let description = [{
+    The `cir.lifetime.start` operation marks the beginning of the live range
+    of the memory region pointed to by `$ptr`. Between this operation and a
+    matching `cir.lifetime.end` on the same pointer, the underlying storage
+    is considered live; outside that range it is considered dead, and the
+    optimizer is free to reuse the storage for other purposes.
+
+    This operation exhibits undefined behavior if:
+      * `$ptr` does not point to memory allocated by `cir.alloca`; or
+      * no matching `cir.lifetime.end` reaches every control-flow path that
+        follows this operation.
+
+    This operation corresponds to the LLVM intrinsic `llvm.lifetime.start`.
+
+    Example:
+    ```
+    cir.lifetime.start %ptr : !cir.ptr<!void>
----------------
xlauko wrote:

It might be helpfull, for this operation to return a token, that is consumed by `cir.liftime.end`?

https://github.com/llvm/llvm-project/pull/199599