[Outlining] Add loop instruction support

Adds support for the loop instruction to be outlined and a test showing a repeat loop being outlined.

Reviewers: tlively

Reviewed By: tlively

Pull Request: #6141

src/passes/Outlining.cpp

@@ -103,6 +103,9 @@ struct ReconstructStringifyWalker
     } else if (reason.getElseStart()) {
       ASSERT_OK(existingBuilder.visitElse());
       DBG(desc = "Else Start at ");
+    } else if (auto curr = reason.getLoopStart()) {
+      ASSERT_OK(existingBuilder.visitLoopStart(curr->loop));
+      DBG(desc = "Loop Start at ");
     } else if (reason.getEnd()) {
       ASSERT_OK(existingBuilder.visitEnd());
       // Outlining performs an unnested walk of the Wasm module, visiting

test/lit/passes/outlining.wast

@@ -726,3 +726,40 @@
 ;; CHECK-NEXT:  (call $outline$)
 ;; CHECK-NEXT:  (call $outline$)
 ;; CHECK-NEXT: )
+
+;; Outline a loop
+;; TODO: Ideally, a loop (like any control flow) repeated within a program can
+;; be outlined by itself. Right now this is not possible since a control flow
+;; is represented by a single symbol and only sequences of symbols >= 2 are
+;; candidates for outlining.
+(module
+  ;; CHECK:      (type $0 (func))
+
+  ;; CHECK:      (func $outline$ (type $0)
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (i32.const 0)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT:  (loop $loop-in
+  ;; CHECK-NEXT:   (nop)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+
+  ;; CHECK:      (func $a (type $0)
+  ;; CHECK-NEXT:  (call $outline$)
+  ;; CHECK-NEXT: )
+  (func $a
+    (drop
+      (i32.const 0)
+    )
+    (loop (nop))
+  )
+  ;; CHECK:      (func $b (type $0)
+  ;; CHECK-NEXT:  (call $outline$)
+  ;; CHECK-NEXT: )
+  (func $b
+    (drop
+      (i32.const 0)
+    )
+    (loop (nop))
+  )
+)