[turbofan] Simplify validity check after dependency installation.

The check was accidentally done only when a stress-flag was enabled.
Moreover, the check is actually unnecessary because the code will deopt
itself once it gets run.

Also add a DCHECK that these invalidations can only happen due to
pretenuring changes.

Bug: v8:8520
Change-Id: Ibb008f93e9e417d2f88cd5fd8fd1380db88bbb85
Reviewed-on: https://chromium-review.googlesource.com/c/1384304Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58395}

src/compiler/compilation-dependencies.cc

@@ -19,6 +19,10 @@ class CompilationDependencies::Dependency : public ZoneObject {
   virtual bool IsValid() const = 0;
   virtual void PrepareInstall() {}
   virtual void Install(const MaybeObjectHandle& code) = 0;
+
+#ifdef DEBUG
+  virtual bool IsPretenureModeDependency() const { return false; }
+#endif
 };
 
 class InitialMapDependency final : public CompilationDependencies::Dependency {
@@ -146,6 +150,10 @@ class PretenureModeDependency final
         DependentCode::kAllocationSiteTenuringChangedGroup);
   }
 
+#ifdef DEBUG
+  bool IsPretenureModeDependency() const override { return true; }
+#endif
+
  private:
   AllocationSiteRef site_;
   PretenureFlag mode_;
@@ -417,15 +425,21 @@ bool CompilationDependencies::Commit(Handle<Code> code) {
     dep->Install(MaybeObjectHandle::Weak(code));
   }
 
+  // It is even possible that a GC during the above installations invalidated
+  // one of the dependencies. However, this should only affect pretenure mode
+  // dependencies, which we assert below. It is safe to return successfully in
+  // these cases, because once the code gets executed it will do a stack check
+  // that triggers its deoptimization.
   if (FLAG_stress_gc_during_compilation) {
     isolate_->heap()->PreciseCollectAllGarbage(
         Heap::kNoGCFlags, GarbageCollectionReason::kTesting,
         kGCCallbackFlagForced);
-    if (!AreValid()) {
-      dependencies_.clear();
-      return false;
-    }
   }
+#ifdef DEBUG
+  for (auto dep : dependencies_) {
+    CHECK_IMPLIES(!dep->IsValid(), dep->IsPretenureModeDependency());
+  }
+#endif
 
   dependencies_.clear();
   return true;