Extend reprocessing assertion failure with context

Bug: 178235885
Change-Id: Ib40be7fca073024eef062b3ac579d4084b133b7a
diff --git a/src/main/java/com/android/tools/r8/ir/conversion/IRConverter.java b/src/main/java/com/android/tools/r8/ir/conversion/IRConverter.java
index 60e2477..152d618 100644
--- a/src/main/java/com/android/tools/r8/ir/conversion/IRConverter.java
+++ b/src/main/java/com/android/tools/r8/ir/conversion/IRConverter.java
@@ -1251,10 +1251,12 @@
       timing.end();
     }
 
-    assert !method.isProcessed() || !isDebugMode;
+    assert !method.isProcessed() || !isDebugMode
+        : "Method already processed: " + context.toSourceString();
     assert !method.isProcessed()
-        || !appView.enableWholeProgramOptimizations()
-        || !appView.appInfo().withLiveness().isNeverReprocessMethod(method.method);
+            || !appView.enableWholeProgramOptimizations()
+            || !appView.appInfo().withLiveness().isNeverReprocessMethod(method.method)
+        : "Illegal reprocessing due to -neverreprocess rule: " + context.toSourceString();
 
     if (lambdaMerger != null) {
       timing.begin("Merge lambdas");