[Mlir-commits] [mlir] [MLIR] Introduce support for early exits (PR #166688)

[Matthias Springer]

================
@@ -146,6 +147,182 @@ def ExecuteRegionOp : SCF_Op<"execute_region", [
 
   let hasVerifier = 1;
 }
+//===----------------------------------------------------------------------===//
+// LoopOp
+//===----------------------------------------------------------------------===//
+
+def LoopOp : SCF_Op<"loop",[
+    AutomaticAllocationScope,
+    OpAsmOpInterface,
+    RecursiveMemoryEffects,
+    PropagateControlFlowBreak,
+    TokenProducerTrait,
+    DeclareOpInterfaceMethods<RegionBranchOpInterface,
+        ["getEntrySuccessorOperands", "getSuccessorInputs"]>,
+    SingleBlockImplicitTerminator<"op_impl::LoopOpImplicitTerminatorType">,
+    HasBreakingControlFlowOpInterface,
+    HasNestedTerminator<["ContinueOp", "BreakOp"]>
+  ]> {
+  let summary = "Loop until a break operation";
+  let description = [{
+    The `loop` operation represents an unstructured infinite loop that executes
+    until a `break` is reached.
+
+    The loop consists of (1) a set of loop-carried values which are initialized by
+    `initValues` and updated by each iteration of the loop, and
+    (2) a region which represents the loop body.
+
+    The loop will execute the body of the loop until a `break` is dynamically executed.
+
+    Each control path of the loop must be terminated by:
+
+    - a `continue` that yields the next iteration's value for each loop carried variable.
+    - a `break` that terminates the loop and yields the final loop carried values.
+
+    As long as each loop iteration is terminated by one of these operations they may be combined with other control
+    flow operations to express different control flow patterns.
+
+    The loop operation produces one return value for each loop carried variable. The type of the `i`-th return
----------------
matthias-springer wrote:

This looks outdated.
- The loop-carried variable types must match the init operand types.
- All users of the token must be `scf.continue` or `scf.break` (?)
- The loop-carried variables types must match the operand types of the `scf.continue` ops that target this op.
- The result types must match the operand types of the `scf.break` ops that target this op.
- Maybe worth pointing out explicitly: if no `scf.break` is targeting this op, then the op can have arbitrary results and their values are undefined. But that's fine because there is no control flow path where these op results are "in scope".


https://github.com/llvm/llvm-project/pull/166688