Fix assertion when analyzing a for-loop with no condition expression

[li.zhe.hua]

Summary

For loops are allowed to have an empty conditional expression; we
should not assert that it must have one.

[ymandel]

Looks like you and Stanislav had the same idea?
https://reviews.llvm.org/D128833

[li.zhe.hua]

In D128848#3620185, @ymandel wrote:

Looks like you and Stanislav had the same idea?
https://reviews.llvm.org/D128833

Seems like it.

clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp

public:
   void VisitDoStmt(const DoStmt *S) {
     auto *Cond = S->getCond();
     assert(Cond != nullptr);
     extendFlowCondition(*Cond);
   }
 
   void VisitForStmt(const ForStmt *S) {
     auto *Cond = S->getCond();
-    assert(Cond != nullptr);
+    if (Cond == nullptr)
+      return;
     extendFlowCondition(*Cond);
   }
 
   void VisitBinaryOperator(const BinaryOperator *S) {
     assert(S->getOpcode() == BO_LAnd || S->getOpcode() == BO_LOr);
     auto *LHS = S->getLHS();
     assert(LHS != nullptr);
     extendFlowCondition(*LHS);

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

 //===- unittests/Analysis/FlowSensitive/TransferTest.cpp ------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "NoopAnalysis.h"
 #include "TestingSupport.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
-#include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
 #include "clang/Analysis/FlowSensitive/StorageLocation.h"
 #include "clang/Analysis/FlowSensitive/Value.h"
 #include "clang/Basic/LangStandard.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Casting.h"
runDataflow(
 
         BoolValue &AfterLoopFooVal =
             *cast<BoolValue>(AfterLoopEnv.getValue(*FooDecl, SkipPast::None));
         EXPECT_TRUE(AfterLoopEnv.flowConditionImplies(
             AfterLoopEnv.makeNot(AfterLoopFooVal)));
       });
 }
 
+TEST_F(TransferTest, ForStmtEmptyBranchExtendsFlowCondition) {
+  std::string Code = R"cc(
+    void target(bool Foo) {
+      for (;;) {
+        if (!Foo) {
+          break;
+        }
+        (void)0;
+        // [[loop_body]]
+      }
+      (void)0;
+      // [[after_loop]]
+    }
+  )cc";
+  runDataflow(
+      Code, [](llvm::ArrayRef<
+                   std::pair<std::string, DataflowAnalysisState<NoopLattice>>>
+                   Results,
+               ASTContext &ASTCtx) {
+        ASSERT_THAT(Results,
+                    ElementsAre(Pair("after_loop", _), Pair("loop_body", _)));
+        const Environment &LoopBodyEnv = Results[1].second.Env;
+        const Environment &AfterLoopEnv = Results[0].second.Env;
+
+        const ValueDecl *FooDecl = findValueDecl(ASTCtx, "Foo");
+        ASSERT_THAT(FooDecl, NotNull());
+
+        BoolValue &LoopBodyFooVal =
+            *cast<BoolValue>(LoopBodyEnv.getValue(*FooDecl, SkipPast::None));
+        EXPECT_TRUE(LoopBodyEnv.flowConditionImplies(LoopBodyFooVal));
+
+        BoolValue &AfterLoopFooVal =
+            *cast<BoolValue>(AfterLoopEnv.getValue(*FooDecl, SkipPast::None));
+        EXPECT_TRUE(AfterLoopEnv.flowConditionImplies(
+            AfterLoopEnv.makeNot(AfterLoopFooVal)));
+      });
+}
+
 } // namespace