Avoid spurious warnings in pass skipping (#5451)

Nested runners should be ignored, as they run some internal stuff in
certain passes, which would not contain the pass the user asked to
skip with --skip-pass.

Author: kripken

src/passes/pass.cpp

@@ -816,13 +816,17 @@ void PassRunner::run() {
     flush();
   }
 
-  // All the passes the user requested to skip should have been seen, and
-  // skipped. If not, the user may have had a typo in the name of a pass to
-  // skip, and we will warn.
-  for (auto pass : options.passesToSkip) {
-    if (!skippedPasses.count(pass)) {
-      std::cerr << "warning: --" << pass << " was requested to be skipped, "
-                << "but it was not found in the passes that were run.\n";
+  if (!isNested) {
+    // All the passes the user requested to skip should have been seen, and
+    // skipped. If not, the user may have had a typo in the name of a pass to
+    // skip, and we will warn. (We don't do this in a nested runner because
+    // those are used for various internal tasks inside passes, which would lead
+    // to many spurious warnings.)
+    for (auto pass : options.passesToSkip) {
+      if (!skippedPasses.count(pass)) {
+        std::cerr << "warning: --" << pass << " was requested to be skipped, "
+                  << "but it was not found in the passes that were run.\n";
+      }
     }
   }
 }

test/lit/passes/O1_skip.wast

@@ -1,11 +1,14 @@
 ;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
 ;; NOTE: This test was ported using port_passes_tests_to_lit.py and could be cleaned up.
 
-;; RUN: foreach %s %t wasm-opt -O2 --coalesce-locals --skip-pass=coalesce-locals -S -o - | filecheck %s
+;; RUN: foreach %s %t wasm-opt -O2 --coalesce-locals --skip-pass=coalesce-locals -S -o - 2>&1 | filecheck %s
 
 ;; We should skip coalese-locals even though it is run in -O2 and also we ask to
 ;; run it directly: the skip instruction overrides everything else.
 
+;; There should also be no warning in the output.
+;; CHECK-NOT: warning:
+
 (module
  ;; CHECK:      (type $i32_i32_=>_none (func (param i32 i32)))