diff --git a/packages/react-dom/src/__tests__/ReactCompositeComponent-test.js b/packages/react-dom/src/__tests__/ReactCompositeComponent-test.js
index 908d418cac7ef..49e107f877ef5 100644
--- a/packages/react-dom/src/__tests__/ReactCompositeComponent-test.js
+++ b/packages/react-dom/src/__tests__/ReactCompositeComponent-test.js
@@ -493,43 +493,6 @@ describe('ReactCompositeComponent', () => {
     ReactDOM.render(<Component prop={123} />, container);
   });
 
-  it('should warn about `setState` in getChildContext', () => {
-    const container = document.createElement('div');
-
-    let renderPasses = 0;
-
-    class Component extends React.Component {
-      state = {value: 0};
-
-      getChildContext() {
-        if (this.state.value === 0) {
-          this.setState({value: 1});
-        }
-      }
-
-      render() {
-        renderPasses++;
-        return <div />;
-      }
-    }
-    Component.childContextTypes = {};
-
-    let instance;
-
-    expect(() => {
-      instance = ReactDOM.render(<Component />, container);
-    }).toErrorDev(
-      'Warning: setState(...): Cannot call setState() inside getChildContext()',
-    );
-
-    expect(renderPasses).toBe(2);
-    expect(instance.state.value).toBe(1);
-
-    // Test deduplication; (no additional warnings are expected).
-    ReactDOM.unmountComponentAtNode(container);
-    ReactDOM.render(<Component />, container);
-  });
-
   it('should cleanup even if render() fatals', () => {
     class BadComponent extends React.Component {
       render() {
diff --git a/packages/react-dom/src/__tests__/ReactDOMComponent-test.js b/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
index 7a0e286399528..1b9e644848894 100644
--- a/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
@@ -1242,53 +1242,6 @@ describe('ReactDOMComponent', () => {
       );
     });
 
-    it('should emit a warning once for a named custom component using shady DOM', () => {
-      const defaultCreateElement = document.createElement.bind(document);
-
-      try {
-        document.createElement = element => {
-          const container = defaultCreateElement(element);
-          container.shadyRoot = {};
-          return container;
-        };
-        class ShadyComponent extends React.Component {
-          render() {
-            return <polymer-component />;
-          }
-        }
-        const node = document.createElement('div');
-        expect(() => ReactDOM.render(<ShadyComponent />, node)).toErrorDev(
-          'ShadyComponent is using shady DOM. Using shady DOM with React can ' +
-            'cause things to break subtly.',
-        );
-        mountComponent({is: 'custom-shady-div2'});
-      } finally {
-        document.createElement = defaultCreateElement;
-      }
-    });
-
-    it('should emit a warning once for an unnamed custom component using shady DOM', () => {
-      const defaultCreateElement = document.createElement.bind(document);
-
-      try {
-        document.createElement = element => {
-          const container = defaultCreateElement(element);
-          container.shadyRoot = {};
-          return container;
-        };
-
-        expect(() => mountComponent({is: 'custom-shady-div'})).toErrorDev(
-          'A component is using shady DOM. Using shady DOM with React can ' +
-            'cause things to break subtly.',
-        );
-
-        // No additional warnings are expected
-        mountComponent({is: 'custom-shady-div2'});
-      } finally {
-        document.createElement = defaultCreateElement;
-      }
-    });
-
     it('should treat menuitem as a void element but still create the closing tag', () => {
       // menuitem is not implemented in jsdom, so this triggers the unknown warning error
       const container = document.createElement('div');
diff --git a/packages/react-dom/src/client/ReactDOMComponent.js b/packages/react-dom/src/client/ReactDOMComponent.js
index 854137dec6fa6..cdf953207d0d1 100644
--- a/packages/react-dom/src/client/ReactDOMComponent.js
+++ b/packages/react-dom/src/client/ReactDOMComponent.js
@@ -7,8 +7,6 @@
  * @flow
  */
 
-// TODO: direct imports like some-package/src/* are bad. Fix me.
-import {getCurrentFiberOwnerNameInDevOrNull} from 'react-reconciler/src/ReactCurrentFiber';
 import {registrationNameModules} from 'legacy-events/EventPluginRegistry';
 import {canUseDOM} from 'shared/ExecutionEnvironment';
 import endsWith from 'shared/endsWith';
@@ -90,7 +88,6 @@ import {
 import {legacyListenToEvent} from '../events/DOMLegacyEventPluginSystem';
 
 let didWarnInvalidHydration = false;
-let didWarnShadyDOM = false;
 let didWarnScriptTags = false;
 
 const DANGEROUSLY_SET_INNER_HTML = 'dangerouslySetInnerHTML';
@@ -509,18 +506,6 @@ export function setInitialProperties(
   const isCustomComponentTag = isCustomComponent(tag, rawProps);
   if (__DEV__) {
     validatePropertiesInDevelopment(tag, rawProps);
-    if (
-      isCustomComponentTag &&
-      !didWarnShadyDOM &&
-      (domElement: any).shadyRoot
-    ) {
-      console.error(
-        '%s is using shady DOM. Using shady DOM with React can ' +
-          'cause things to break subtly.',
-        getCurrentFiberOwnerNameInDevOrNull() || 'A component',
-      );
-      didWarnShadyDOM = true;
-    }
   }
 
   // TODO: Make sure that we check isMounted before firing any of these events.
@@ -906,18 +891,6 @@ export function diffHydratedProperties(
     suppressHydrationWarning = rawProps[SUPPRESS_HYDRATION_WARNING] === true;
     isCustomComponentTag = isCustomComponent(tag, rawProps);
     validatePropertiesInDevelopment(tag, rawProps);
-    if (
-      isCustomComponentTag &&
-      !didWarnShadyDOM &&
-      (domElement: any).shadyRoot
-    ) {
-      console.error(
-        '%s is using shady DOM. Using shady DOM with React can ' +
-          'cause things to break subtly.',
-        getCurrentFiberOwnerNameInDevOrNull() || 'A component',
-      );
-      didWarnShadyDOM = true;
-    }
   }
 
   // TODO: Make sure that we check isMounted before firing any of these events.
diff --git a/packages/react-reconciler/src/ReactCurrentFiber.js b/packages/react-reconciler/src/ReactCurrentFiber.js
index 47baa167eb3d6..d6096791b674a 100644
--- a/packages/react-reconciler/src/ReactCurrentFiber.js
+++ b/packages/react-reconciler/src/ReactCurrentFiber.js
@@ -23,8 +23,6 @@ import getComponentName from 'shared/getComponentName';
 
 const ReactDebugCurrentFrame = ReactSharedInternals.ReactDebugCurrentFrame;
 
-type LifeCyclePhase = 'render' | 'getChildContext';
-
 function describeFiber(fiber: Fiber): string {
   switch (fiber.tag) {
     case HostRoot:
@@ -57,7 +55,7 @@ export function getStackByFiberInDevAndProd(workInProgress: Fiber): string {
 }
 
 export let current: Fiber | null = null;
-export let phase: LifeCyclePhase | null = null;
+export let isRendering: boolean = false;
 
 export function getCurrentFiberOwnerNameInDevOrNull(): string | null {
   if (__DEV__) {
@@ -88,7 +86,7 @@ export function resetCurrentFiber() {
   if (__DEV__) {
     ReactDebugCurrentFrame.getCurrentStack = null;
     current = null;
-    phase = null;
+    isRendering = false;
   }
 }
 
@@ -96,12 +94,12 @@ export function setCurrentFiber(fiber: Fiber) {
   if (__DEV__) {
     ReactDebugCurrentFrame.getCurrentStack = getCurrentFiberStackInDev;
     current = fiber;
-    phase = null;
+    isRendering = false;
   }
 }
 
-export function setCurrentPhase(lifeCyclePhase: LifeCyclePhase | null) {
+export function setIsRendering(rendering: boolean) {
   if (__DEV__) {
-    phase = lifeCyclePhase;
+    isRendering = rendering;
   }
 }
diff --git a/packages/react-reconciler/src/ReactFiberBeginWork.js b/packages/react-reconciler/src/ReactFiberBeginWork.js
index 8eb9f9ffb9502..ddbdacd61a1dc 100644
--- a/packages/react-reconciler/src/ReactFiberBeginWork.js
+++ b/packages/react-reconciler/src/ReactFiberBeginWork.js
@@ -74,9 +74,9 @@ import ReactStrictModeWarnings from './ReactStrictModeWarnings';
 import {refineResolvedLazyComponent} from 'shared/ReactLazyComponent';
 import {REACT_LAZY_TYPE, getIteratorFn} from 'shared/ReactSymbols';
 import {
-  setCurrentPhase,
   getCurrentFiberOwnerNameInDevOrNull,
   getCurrentFiberStackInDev,
+  setIsRendering,
 } from './ReactCurrentFiber';
 import {startWorkTimer, cancelWorkTimer} from './ReactDebugFiberPerf';
 import {
@@ -193,7 +193,6 @@ let didWarnAboutContextTypeOnFunctionComponent;
 let didWarnAboutGetDerivedStateOnFunctionComponent;
 let didWarnAboutFunctionRefs;
 export let didWarnAboutReassigningProps;
-let didWarnAboutMaxDuration;
 let didWarnAboutRevealOrder;
 let didWarnAboutTailOptions;
 let didWarnAboutDefaultPropsOnFunctionComponent;
@@ -205,7 +204,6 @@ if (__DEV__) {
   didWarnAboutGetDerivedStateOnFunctionComponent = {};
   didWarnAboutFunctionRefs = {};
   didWarnAboutReassigningProps = false;
-  didWarnAboutMaxDuration = false;
   didWarnAboutRevealOrder = {};
   didWarnAboutTailOptions = {};
   didWarnAboutDefaultPropsOnFunctionComponent = {};
@@ -312,7 +310,7 @@ function updateForwardRef(
   prepareToReadContext(workInProgress, renderExpirationTime);
   if (__DEV__) {
     ReactCurrentOwner.current = workInProgress;
-    setCurrentPhase('render');
+    setIsRendering(true);
     nextChildren = renderWithHooks(
       current,
       workInProgress,
@@ -337,7 +335,7 @@ function updateForwardRef(
         );
       }
     }
-    setCurrentPhase(null);
+    setIsRendering(false);
   } else {
     nextChildren = renderWithHooks(
       current,
@@ -644,7 +642,7 @@ function updateFunctionComponent(
   prepareToReadContext(workInProgress, renderExpirationTime);
   if (__DEV__) {
     ReactCurrentOwner.current = workInProgress;
-    setCurrentPhase('render');
+    setIsRendering(true);
     nextChildren = renderWithHooks(
       current,
       workInProgress,
@@ -669,7 +667,7 @@ function updateFunctionComponent(
         );
       }
     }
-    setCurrentPhase(null);
+    setIsRendering(false);
   } else {
     nextChildren = renderWithHooks(
       current,
@@ -720,7 +718,7 @@ function updateBlock(
   prepareToReadContext(workInProgress, renderExpirationTime);
   if (__DEV__) {
     ReactCurrentOwner.current = workInProgress;
-    setCurrentPhase('render');
+    setIsRendering(true);
     nextChildren = renderWithHooks(
       current,
       workInProgress,
@@ -745,7 +743,7 @@ function updateBlock(
         );
       }
     }
-    setCurrentPhase(null);
+    setIsRendering(false);
   } else {
     nextChildren = renderWithHooks(
       current,
@@ -923,7 +921,7 @@ function finishClassComponent(
     }
   } else {
     if (__DEV__) {
-      setCurrentPhase('render');
+      setIsRendering(true);
       nextChildren = instance.render();
       if (
         debugRenderPhaseSideEffectsForStrictMode &&
@@ -931,7 +929,7 @@ function finishClassComponent(
       ) {
         instance.render();
       }
-      setCurrentPhase(null);
+      setIsRendering(false);
     } else {
       nextChildren = instance.render();
     }
@@ -1637,18 +1635,6 @@ function updateSuspenseComponent(
 
   pushSuspenseContext(workInProgress, suspenseContext);
 
-  if (__DEV__) {
-    if ('maxDuration' in nextProps) {
-      if (!didWarnAboutMaxDuration) {
-        didWarnAboutMaxDuration = true;
-        console.error(
-          'maxDuration has been removed from React. ' +
-            'Remove the maxDuration prop.',
-        );
-      }
-    }
-  }
-
   // This next part is a bit confusing. If the children timeout, we switch to
   // showing the fallback children in place of the "primary" children.
   // However, we don't want to delete the primary children because then their
@@ -2732,9 +2718,9 @@ function updateContextConsumer(
   let newChildren;
   if (__DEV__) {
     ReactCurrentOwner.current = workInProgress;
-    setCurrentPhase('render');
+    setIsRendering(true);
     newChildren = render(newValue);
-    setCurrentPhase(null);
+    setIsRendering(false);
   } else {
     newChildren = render(newValue);
   }
diff --git a/packages/react-reconciler/src/ReactFiberContext.js b/packages/react-reconciler/src/ReactFiberContext.js
index 946d33606c813..5f4375b4c5c1f 100644
--- a/packages/react-reconciler/src/ReactFiberContext.js
+++ b/packages/react-reconciler/src/ReactFiberContext.js
@@ -17,7 +17,7 @@ import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
 import checkPropTypes from 'prop-types/checkPropTypes';
 
-import {setCurrentPhase, getCurrentFiberStackInDev} from './ReactCurrentFiber';
+import {getCurrentFiberStackInDev} from './ReactCurrentFiber';
 import {startPhaseTimer, stopPhaseTimer} from './ReactDebugFiberPerf';
 import {createCursor, push, pop} from './ReactFiberStack';
 
@@ -210,15 +210,9 @@ function processChildContext(
     }
 
     let childContext;
-    if (__DEV__) {
-      setCurrentPhase('getChildContext');
-    }
     startPhaseTimer(fiber, 'getChildContext');
     childContext = instance.getChildContext();
     stopPhaseTimer();
-    if (__DEV__) {
-      setCurrentPhase(null);
-    }
     for (let contextKey in childContext) {
       invariant(
         contextKey in childContextTypes,
diff --git a/packages/react-reconciler/src/ReactFiberReconciler.js b/packages/react-reconciler/src/ReactFiberReconciler.js
index 8102f66c25f65..816a3946562e1 100644
--- a/packages/react-reconciler/src/ReactFiberReconciler.js
+++ b/packages/react-reconciler/src/ReactFiberReconciler.js
@@ -70,7 +70,7 @@ import {
 import {createUpdate, enqueueUpdate} from './ReactUpdateQueue';
 import {
   getStackByFiberInDevAndProd,
-  phase as ReactCurrentFiberPhase,
+  isRendering as ReactCurrentFiberIsRendering,
   current as ReactCurrentFiberCurrent,
 } from './ReactCurrentFiber';
 import {StrictMode} from './ReactTypeOfMode';
@@ -259,7 +259,7 @@ export function updateContainer(
 
   if (__DEV__) {
     if (
-      ReactCurrentFiberPhase === 'render' &&
+      ReactCurrentFiberIsRendering &&
       ReactCurrentFiberCurrent !== null &&
       !didWarnAboutNestedUpdates
     ) {
diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.js b/packages/react-reconciler/src/ReactFiberWorkLoop.js
index 3c2427594a798..1272338f75ad7 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.js
@@ -156,7 +156,7 @@ import {
 import getComponentName from 'shared/getComponentName';
 import ReactStrictModeWarnings from './ReactStrictModeWarnings';
 import {
-  phase as ReactCurrentDebugFiberPhaseInDEV,
+  isRendering as ReactCurrentDebugFiberIsRenderingInDEV,
   resetCurrentFiber as resetCurrentDebugFiberInDEV,
   setCurrentFiber as setCurrentDebugFiberInDEV,
   getStackByFiberInDevAndProd,
@@ -2793,7 +2793,6 @@ if (__DEV__ && replayFailedUnitOfWorkWithInvokeGuardedCallback) {
 }
 
 let didWarnAboutUpdateInRender = false;
-let didWarnAboutUpdateInGetChildContext = false;
 function warnAboutRenderPhaseUpdatesInDEV(fiber) {
   if (__DEV__) {
     if ((executionContext & RenderContext) !== NoContext) {
@@ -2808,29 +2807,18 @@ function warnAboutRenderPhaseUpdatesInDEV(fiber) {
           break;
         }
         case ClassComponent: {
-          switch (ReactCurrentDebugFiberPhaseInDEV) {
-            case 'getChildContext':
-              if (didWarnAboutUpdateInGetChildContext) {
-                return;
-              }
-              console.error(
-                'setState(...): Cannot call setState() inside getChildContext()',
-              );
-              didWarnAboutUpdateInGetChildContext = true;
-              break;
-            case 'render':
-              if (didWarnAboutUpdateInRender) {
-                return;
-              }
-              console.error(
-                'Cannot update during an existing state transition (such as ' +
-                  'within `render`). Render methods should be a pure ' +
-                  'function of props and state.',
-              );
-              didWarnAboutUpdateInRender = true;
-              break;
+          if (
+            ReactCurrentDebugFiberIsRenderingInDEV &&
+            !didWarnAboutUpdateInRender
+          ) {
+            console.error(
+              'Cannot update during an existing state transition (such as ' +
+                'within `render`). Render methods should be a pure ' +
+                'function of props and state.',
+            );
+            didWarnAboutUpdateInRender = true;
+            break;
           }
-          break;
         }
       }
     }
diff --git a/packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.internal.js b/packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.internal.js
index 0cca771b1df22..0df7431977cf2 100644
--- a/packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.internal.js
@@ -110,25 +110,6 @@ function loadModules({
         }
       }
 
-      it('warns if the deprecated maxDuration option is used', () => {
-        function Foo() {
-          return (
-            <Suspense maxDuration={100} fallback="Loading...">
-              <div />;
-            </Suspense>
-          );
-        }
-
-        ReactNoop.render(<Foo />);
-
-        expect(() => Scheduler.unstable_flushAll()).toErrorDev([
-          'Warning: maxDuration has been removed from React. ' +
-            'Remove the maxDuration prop.' +
-            '\n    in Suspense (at **)' +
-            '\n    in Foo (at **)',
-        ]);
-      });
-
       it('does not restart rendering for initial render', async () => {
         function Bar(props) {
           Scheduler.unstable_yieldValue('Bar');