[NewPM] Only verify loop for nonskipped user loop pass

No verification for pass mangers since it is not needed.
No verification for skipped loop pass since the asserted condition is not used.

Add a BeforeNonSkippedPass callback for this. The callback needs more
inputs than its parameters to work so the callback is added on-the-fly.

Reviewed By: aeubanks, asbirlea

Differential Revision: https://reviews.llvm.org/D84977

Author: Yuanfang Chen

llvm/include/llvm/IR/PassInstrumentation.h

@@ -243,6 +243,16 @@ class PassInstrumentation {
                   ExtraArgsT...) {
     return false;
   }
+
+  template <typename CallableT>
+  void pushBeforeNonSkippedPassCallback(CallableT C) {
+    if (Callbacks)
+      Callbacks->BeforeNonSkippedPassCallbacks.emplace_back(std::move(C));
+  }
+  void popBeforeNonSkippedPassCallback() {
+    if (Callbacks)
+      Callbacks->BeforeNonSkippedPassCallbacks.pop_back();
+  }
 };
 
 bool isSpecialPass(StringRef PassID, const std::vector<StringRef> &Specials);

llvm/include/llvm/Transforms/Scalar/LoopPassManager.h

@@ -50,6 +50,7 @@
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/IR/Dominators.h"
+#include "llvm/IR/PassInstrumentation.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/Transforms/Utils/LCSSA.h"
 #include "llvm/Transforms/Utils/LoopSimplify.h"
@@ -296,6 +297,21 @@ class FunctionToLoopPassAdaptor
     // declaration.
     appendLoopsToWorklist(LI, Worklist);
 
+#ifndef NDEBUG
+    PI.pushBeforeNonSkippedPassCallback([&LAR, &LI](StringRef PassID, Any IR) {
+      if (isSpecialPass(PassID, {"PassManager"}))
+        return;
+      assert(any_isa<const Loop *>(IR));
+      const Loop *L = any_cast<const Loop *>(IR);
+      assert(L && "Loop should be valid for printing");
+
+      // Verify the loop structure and LCSSA form before visiting the loop.
+      L->verifyLoop();
+      assert(L->isRecursivelyLCSSAForm(LAR.DT, LI) &&
+             "Loops must remain in LCSSA form!");
+    });
+#endif
+
     do {
       Loop *L = Worklist.pop_back_val();
 
@@ -306,11 +322,6 @@ class FunctionToLoopPassAdaptor
 #ifndef NDEBUG
       // Save a parent loop pointer for asserts.
       Updater.ParentL = L->getParentLoop();
-
-      // Verify the loop structure and LCSSA form before visiting the loop.
-      L->verifyLoop();
-      assert(L->isRecursivelyLCSSAForm(LAR.DT, LI) &&
-             "Loops must remain in LCSSA form!");
 #endif
       // Check the PassInstrumentation's BeforePass callbacks before running the
       // pass, skip its execution completely if asked to (callback returns
@@ -345,6 +356,10 @@ class FunctionToLoopPassAdaptor
       PA.intersect(std::move(PassPA));
     } while (!Worklist.empty());
 
+#ifndef NDEBUG
+    PI.popBeforeNonSkippedPassCallback();
+#endif
+
     // By definition we preserve the proxy. We also preserve all analyses on
     // Loops. This precludes *any* invalidation of loop analyses by the proxy,
     // but that's OK because we've taken care to invalidate analyses in the

llvm/lib/Transforms/Scalar/LoopPassManager.cpp

@@ -57,13 +57,6 @@ PassManager<Loop, LoopAnalysisManager, LoopStandardAnalysisResults &,
       break;
     }
 
-#ifndef NDEBUG
-    // Verify the loop structure and LCSSA form before visiting the loop.
-    L.verifyLoop();
-    assert(L.isRecursivelyLCSSAForm(AR.DT, AR.LI) &&
-           "Loops must remain in LCSSA form!");
-#endif
-
     // Update the analysis manager as each pass runs and potentially
     // invalidates analyses.
     AM.invalidate(L, PassPA);

llvm/test/Feature/optnone-opt.ll

@@ -34,7 +34,7 @@ while.body:                                       ; preds = %while.cond
   br label %while.cond
 
 while.end:                                        ; preds = %while.cond
-  ret i32 0
+  ret i32 %dec
 }
 
 attributes #0 = { optnone noinline }