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[analyzer][IDF] Add a control dependency calculator + a new debug checker 

I intend to improve the analyzer's bug reports by tracking condition
expressions.

01 bool b = messyComputation();
02 int i = 0;
03 if (b) // control dependency of the bug site, let's explain why we assume val
04        // to be true
05   10 / i; // warn: division by zero

I'll detail this heuristic in the followup patch, strictly related to this one
however:

* Create the new ControlDependencyCalculator class that uses llvm::IDFCalculator
  to (lazily) calculate control dependencies for Clang's CFG.
* A new debug checker debug.DumpControlDependencies is added for lit tests
* Add unittests

Differential Revision: https://reviews.llvm.org/D62619

llvm-svn: 365197
This commit is contained in:
Kristof Umann 2019-07-05 12:17:44 +00:00
parent 6884d5e040
commit 5e17ee1e35
7 changed files with 326 additions and 28 deletions
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97
clang/include/clang/Analysis/Analyses/Dominators.h
View File

@ -18,6 +18,7 @@
#include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/GraphTraits.h" #include "llvm/ADT/GraphTraits.h"
#include "llvm/ADT/iterator.h" #include "llvm/ADT/iterator.h"
#include "llvm/Support/GenericIteratedDominanceFrontier.h"
#include "llvm/Support/GenericDomTree.h" #include "llvm/Support/GenericDomTree.h"
#include "llvm/Support/GenericDomTreeConstruction.h" #include "llvm/Support/GenericDomTreeConstruction.h"
#include "llvm/Support/raw_ostream.h" #include "llvm/Support/raw_ostream.h"
@ -44,12 +45,17 @@ class CFGDominatorTreeImpl : public ManagedAnalysis {
public: public:
using DominatorTreeBase = llvm::DominatorTreeBase<CFGBlock, IsPostDom>; using DominatorTreeBase = llvm::DominatorTreeBase<CFGBlock, IsPostDom>;
DominatorTreeBase DT;
CFGDominatorTreeImpl() = default; CFGDominatorTreeImpl() = default;
CFGDominatorTreeImpl(CFG *cfg) {
buildDominatorTree(cfg);
}
~CFGDominatorTreeImpl() override = default; ~CFGDominatorTreeImpl() override = default;
DominatorTreeBase& getBase() { return *DT; } DominatorTreeBase &getBase() { return DT; }
CFG *getCFG() { return cfg; }
/// \returns the root CFGBlock of the dominators tree. /// \returns the root CFGBlock of the dominators tree.
CFGBlock *getRoot() const { CFGBlock *getRoot() const {
@ -172,11 +178,96 @@ public:
private: private:
CFG *cfg; CFG *cfg;
DominatorTreeBase DT;
}; };
using CFGDomTree = CFGDominatorTreeImpl</*IsPostDom*/ false>; using CFGDomTree = CFGDominatorTreeImpl</*IsPostDom*/ false>;
using CFGPostDomTree = CFGDominatorTreeImpl</*IsPostDom*/ true>; using CFGPostDomTree = CFGDominatorTreeImpl</*IsPostDom*/ true>;
} // end of namespace clang
namespace llvm {
namespace IDFCalculatorDetail {
/// Specialize ChildrenGetterTy to skip nullpointer successors.
template <bool IsPostDom>
struct ChildrenGetterTy<clang::CFGBlock, IsPostDom> {
using NodeRef = typename GraphTraits<clang::CFGBlock>::NodeRef;
using ChildrenTy = SmallVector<NodeRef, 8>;
ChildrenTy get(const NodeRef &N) {
using OrderedNodeTy =
typename IDFCalculatorBase<clang::CFGBlock, IsPostDom>::OrderedNodeTy;
auto Children = children<OrderedNodeTy>(N);
ChildrenTy Ret{Children.begin(), Children.end()};
Ret.erase(std::remove(Ret.begin(), Ret.end(), nullptr), Ret.end());
return Ret;
}
};
} // end of namespace IDFCalculatorDetail
} // end of namespace llvm
namespace clang {
class ControlDependencyCalculator : public ManagedAnalysis {
using IDFCalculator = llvm::IDFCalculatorBase<CFGBlock, /*IsPostDom=*/true>;
using CFGBlockVector = llvm::SmallVector<CFGBlock *, 4>;
using CFGBlockSet = llvm::SmallPtrSet<CFGBlock *, 4>;
CFGPostDomTree PostDomTree;
IDFCalculator IDFCalc;
llvm::DenseMap<CFGBlock *, CFGBlockVector> ControlDepenencyMap;
public:
ControlDependencyCalculator(CFG *cfg)
: PostDomTree(cfg), IDFCalc(PostDomTree.getBase()) {}
const CFGPostDomTree &getCFGPostDomTree() const { return PostDomTree; }
// Lazily retrieves the set of control dependencies to \p A.
const CFGBlockVector &getControlDependencies(CFGBlock *A) {
auto It = ControlDepenencyMap.find(A);
if (It == ControlDepenencyMap.end()) {
CFGBlockSet DefiningBlock = {A};
IDFCalc.setDefiningBlocks(DefiningBlock);
CFGBlockVector ControlDependencies;
IDFCalc.calculate(ControlDependencies);
It = ControlDepenencyMap.insert({A, ControlDependencies}).first;
}
assert(It != ControlDepenencyMap.end());
return It->second;
}
/// Whether \p A is control dependent on \p B.
bool isControlDependent(CFGBlock *A, CFGBlock *B) {
return llvm::is_contained(getControlDependencies(A), B);
}
// Dumps immediate control dependencies for each block.
LLVM_DUMP_METHOD void dump() {
CFG *cfg = PostDomTree.getCFG();
llvm::errs() << "Control dependencies (Node#,Dependency#):\n";
for (CFGBlock *BB : *cfg) {
assert(BB &&
"LLVM's Dominator tree builder uses nullpointers to signify the "
"virtual root!");
for (CFGBlock *isControlDependency : getControlDependencies(BB))
llvm::errs() << "(" << BB->getBlockID()
<< ","
<< isControlDependency->getBlockID()
<< ")\n";
}
}
};
} // namespace clang } // namespace clang
namespace llvm { namespace llvm {

12
clang/include/clang/Analysis/CFG.h
View File

@ -1285,6 +1285,9 @@ template <> struct GraphTraits< ::clang::CFGBlock *> {
static ChildIteratorType child_end(NodeRef N) { return N->succ_end(); } static ChildIteratorType child_end(NodeRef N) { return N->succ_end(); }
}; };
template <> struct GraphTraits<clang::CFGBlock>
: GraphTraits<clang::CFGBlock *> {};
template <> struct GraphTraits< const ::clang::CFGBlock *> { template <> struct GraphTraits< const ::clang::CFGBlock *> {
using NodeRef = const ::clang::CFGBlock *; using NodeRef = const ::clang::CFGBlock *;
using ChildIteratorType = ::clang::CFGBlock::const_succ_iterator; using ChildIteratorType = ::clang::CFGBlock::const_succ_iterator;
@ -1294,6 +1297,9 @@ template <> struct GraphTraits< const ::clang::CFGBlock *> {
static ChildIteratorType child_end(NodeRef N) { return N->succ_end(); } static ChildIteratorType child_end(NodeRef N) { return N->succ_end(); }
}; };
template <> struct GraphTraits<const clang::CFGBlock>
: GraphTraits<clang::CFGBlock *> {};
template <> struct GraphTraits<Inverse< ::clang::CFGBlock *>> { template <> struct GraphTraits<Inverse< ::clang::CFGBlock *>> {
using NodeRef = ::clang::CFGBlock *; using NodeRef = ::clang::CFGBlock *;
using ChildIteratorType = ::clang::CFGBlock::const_pred_iterator; using ChildIteratorType = ::clang::CFGBlock::const_pred_iterator;
@ -1306,6 +1312,9 @@ template <> struct GraphTraits<Inverse< ::clang::CFGBlock *>> {
static ChildIteratorType child_end(NodeRef N) { return N->pred_end(); } static ChildIteratorType child_end(NodeRef N) { return N->pred_end(); }
}; };
template <> struct GraphTraits<Inverse<clang::CFGBlock>>
: GraphTraits<clang::CFGBlock *> {};
template <> struct GraphTraits<Inverse<const ::clang::CFGBlock *>> { template <> struct GraphTraits<Inverse<const ::clang::CFGBlock *>> {
using NodeRef = const ::clang::CFGBlock *; using NodeRef = const ::clang::CFGBlock *;
using ChildIteratorType = ::clang::CFGBlock::const_pred_iterator; using ChildIteratorType = ::clang::CFGBlock::const_pred_iterator;
@ -1318,6 +1327,9 @@ template <> struct GraphTraits<Inverse<const ::clang::CFGBlock *>> {
static ChildIteratorType child_end(NodeRef N) { return N->pred_end(); } static ChildIteratorType child_end(NodeRef N) { return N->pred_end(); }
}; };
template <> struct GraphTraits<const Inverse<clang::CFGBlock>>
: GraphTraits<clang::CFGBlock *> {};
// Traits for: CFG // Traits for: CFG
template <> struct GraphTraits< ::clang::CFG* > template <> struct GraphTraits< ::clang::CFG* >

4
clang/include/clang/StaticAnalyzer/Checkers/Checkers.td
View File

@ -1237,6 +1237,10 @@ def PostDominatorsTreeDumper : Checker<"DumpPostDominators">,
HelpText<"Print the post dominance tree for a given CFG">, HelpText<"Print the post dominance tree for a given CFG">,
Documentation<NotDocumented>; Documentation<NotDocumented>;
def ControlDependencyTreeDumper : Checker<"DumpControlDependencies">,
HelpText<"Print the post control dependency tree for a given CFG">,
Documentation<NotDocumented>;
def LiveVariablesDumper : Checker<"DumpLiveVars">, def LiveVariablesDumper : Checker<"DumpLiveVars">,
HelpText<"Print results of live variable analysis">, HelpText<"Print results of live variable analysis">,
Documentation<NotDocumented>; Documentation<NotDocumented>;

37
clang/lib/StaticAnalyzer/Checkers/DebugCheckers.cpp
View File

@ -35,9 +35,9 @@ public:
void checkASTCodeBody(const Decl *D, AnalysisManager& mgr, void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
BugReporter &BR) const { BugReporter &BR) const {
if (AnalysisDeclContext *AC = mgr.getAnalysisDeclContext(D)) { if (AnalysisDeclContext *AC = mgr.getAnalysisDeclContext(D)) {
CFGDomTree dom; CFGDomTree Dom;
dom.buildDominatorTree(AC->getCFG()); Dom.buildDominatorTree(AC->getCFG());
dom.dump(); Dom.dump();
} }
} }
}; };
@ -61,9 +61,9 @@ public:
void checkASTCodeBody(const Decl *D, AnalysisManager& mgr, void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
BugReporter &BR) const { BugReporter &BR) const {
if (AnalysisDeclContext *AC = mgr.getAnalysisDeclContext(D)) { if (AnalysisDeclContext *AC = mgr.getAnalysisDeclContext(D)) {
CFGPostDomTree dom; CFGPostDomTree Dom;
dom.buildDominatorTree(AC->getCFG()); Dom.buildDominatorTree(AC->getCFG());
dom.dump(); Dom.dump();
} }
} }
}; };
@ -77,6 +77,31 @@ bool ento::shouldRegisterPostDominatorsTreeDumper(const LangOptions &LO) {
return true; return true;
} }
//===----------------------------------------------------------------------===//
// ControlDependencyTreeDumper
//===----------------------------------------------------------------------===//
namespace {
class ControlDependencyTreeDumper : public Checker<check::ASTCodeBody> {
public:
void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
BugReporter &BR) const {
if (AnalysisDeclContext *AC = mgr.getAnalysisDeclContext(D)) {
ControlDependencyCalculator Dom(AC->getCFG());
Dom.dump();
}
}
};
}
void ento::registerControlDependencyTreeDumper(CheckerManager &mgr) {
mgr.registerChecker<ControlDependencyTreeDumper>();
}
bool ento::shouldRegisterControlDependencyTreeDumper(const LangOptions &LO) {
return true;
}
//===----------------------------------------------------------------------===// //===----------------------------------------------------------------------===//
// LiveVariablesDumper // LiveVariablesDumper
//===----------------------------------------------------------------------===// //===----------------------------------------------------------------------===//

86
clang/test/Analysis/domtest.c
View File

@ -1,6 +1,7 @@
// RUN: %clang_analyze_cc1 %s \ // RUN: %clang_analyze_cc1 %s \
// RUN: -analyzer-checker=debug.DumpDominators \ // RUN: -analyzer-checker=debug.DumpDominators \
// RUN: -analyzer-checker=debug.DumpPostDominators \ // RUN: -analyzer-checker=debug.DumpPostDominators \
// RUN: -analyzer-checker=debug.DumpControlDependencies \
// RUN: 2>&1 | FileCheck %s // RUN: 2>&1 | FileCheck %s
// Test the DominatorsTree implementation with various control flows // Test the DominatorsTree implementation with various control flows
@ -32,7 +33,16 @@ int test1()
// V // V
// [B1] -> [B0 (EXIT)] // [B1] -> [B0 (EXIT)]
// CHECK: Immediate dominance tree (Node#,IDom#): // CHECK: Control dependencies (Node#,Dependency#):
// CHECK-NEXT: (2,7)
// CHECK-NEXT: (3,7)
// CHECK-NEXT: (4,6)
// CHECK-NEXT: (4,7)
// CHECK-NEXT: (5,6)
// CHECK-NEXT: (5,7)
// CHECK-NEXT: (6,7)
// CHECK-NEXT: (7,7)
// CHECK-NEXT: Immediate dominance tree (Node#,IDom#):
// CHECK-NEXT: (0,1) // CHECK-NEXT: (0,1)
// CHECK-NEXT: (1,7) // CHECK-NEXT: (1,7)
// CHECK-NEXT: (2,3) // CHECK-NEXT: (2,3)
@ -80,7 +90,15 @@ int test2()
// / V // / V
// [B7 (ENTRY)] -> [B6] -> [B5] -> [B1] -> [B0 (EXIT)] // [B7 (ENTRY)] -> [B6] -> [B5] -> [B1] -> [B0 (EXIT)]
// CHECK: Immediate dominance tree (Node#,IDom#): // CHECK: Control dependencies (Node#,Dependency#):
// CHECK-NEXT: (2,4)
// CHECK-NEXT: (2,6)
// CHECK-NEXT: (3,4)
// CHECK-NEXT: (3,6)
// CHECK-NEXT: (4,6)
// CHECK-NEXT: (4,4)
// CHECK-NEXT: (5,6)
// CHECK-NEXT: Immediate dominance tree (Node#,IDom#):
// CHECK-NEXT: (0,1) // CHECK-NEXT: (0,1)
// CHECK-NEXT: (1,6) // CHECK-NEXT: (1,6)
// CHECK-NEXT: (2,3) // CHECK-NEXT: (2,3)
@ -117,17 +135,29 @@ int test3()
return 0; return 0;
} }
// <------------- // <- [B2] <-
// / \ // / \
// | ---> [B2] // [B8 (ENTRY)] -> [B7] -> [B6] ---> [B5] -> [B4] -> [B3]
// | /
// [B8 (ENTRY)] -> [B7] -> [B6] -> [B5] -> [B4] -> [B3]
// \ | \ / // \ | \ /
// \ | <------------- // \ | <-------------
// \ \ // \ \
// --------> [B1] -> [B0 (EXIT)] // --------> [B1] -> [B0 (EXIT)]
// CHECK: Immediate dominance tree (Node#,IDom#): // CHECK: Control dependencies (Node#,Dependency#):
// CHECK-NEXT: (2,6)
// CHECK-NEXT: (2,7)
// CHECK-NEXT: (3,5)
// CHECK-NEXT: (3,6)
// CHECK-NEXT: (3,7)
// CHECK-NEXT: (4,5)
// CHECK-NEXT: (4,6)
// CHECK-NEXT: (4,7)
// CHECK-NEXT: (5,6)
// CHECK-NEXT: (5,5)
// CHECK-NEXT: (5,7)
// CHECK-NEXT: (6,7)
// CHECK-NEXT: (6,6)
// CHECK-NEXT: Immediate dominance tree (Node#,IDom#):
// CHECK-NEXT: (0,1) // CHECK-NEXT: (0,1)
// CHECK-NEXT: (1,7) // CHECK-NEXT: (1,7)
// CHECK-NEXT: (2,5) // CHECK-NEXT: (2,5)
@ -176,7 +206,29 @@ int test4()
// \ // \
// -> [B1] -> [B0 (EXIT)] // -> [B1] -> [B0 (EXIT)]
// CHECK: Immediate dominance tree (Node#,IDom#): // CHECK: Control dependencies (Node#,Dependency#):
// CHECK-NEXT: (2,10)
// CHECK-NEXT: (3,5)
// CHECK-NEXT: (3,9)
// CHECK-NEXT: (3,10)
// CHECK-NEXT: (4,5)
// CHECK-NEXT: (4,9)
// CHECK-NEXT: (4,10)
// CHECK-NEXT: (5,9)
// CHECK-NEXT: (5,5)
// CHECK-NEXT: (5,10)
// CHECK-NEXT: (6,8)
// CHECK-NEXT: (6,9)
// CHECK-NEXT: (6,10)
// CHECK-NEXT: (7,8)
// CHECK-NEXT: (7,9)
// CHECK-NEXT: (7,10)
// CHECK-NEXT: (8,9)
// CHECK-NEXT: (8,8)
// CHECK-NEXT: (8,10)
// CHECK-NEXT: (9,10)
// CHECK-NEXT: (10,10)
// CHECK-NEXT: Immediate dominance tree (Node#,IDom#):
// CHECK-NEXT: (0,1) // CHECK-NEXT: (0,1)
// CHECK-NEXT: (1,10) // CHECK-NEXT: (1,10)
// CHECK-NEXT: (2,9) // CHECK-NEXT: (2,9)
@ -242,7 +294,23 @@ int test5()
// V [B4] -----------------> / // V [B4] -----------------> /
// [B2]---------------------------------> // [B2]--------------------------------->
// CHECK: Immediate dominance tree (Node#,IDom#): // CHECK: Control dependencies (Node#,Dependency#):
// CHECK-NEXT: (2,10)
// CHECK-NEXT: (3,10)
// CHECK-NEXT: (4,9)
// CHECK-NEXT: (4,10)
// CHECK-NEXT: (5,9)
// CHECK-NEXT: (5,10)
// CHECK-NEXT: (6,8)
// CHECK-NEXT: (6,9)
// CHECK-NEXT: (6,10)
// CHECK-NEXT: (7,8)
// CHECK-NEXT: (7,9)
// CHECK-NEXT: (7,10)
// CHECK-NEXT: (8,9)
// CHECK-NEXT: (8,10)
// CHECK-NEXT: (9,10)
// CHECK-NEXT: Immediate dominance tree (Node#,IDom#):
// CHECK-NEXT: (0,1) // CHECK-NEXT: (0,1)
// CHECK-NEXT: (1,10) // CHECK-NEXT: (1,10)
// CHECK-NEXT: (2,10) // CHECK-NEXT: (2,10)

21
clang/test/Analysis/domtest.cpp
View File

@ -1,6 +1,7 @@
// RUN: %clang_analyze_cc1 %s \ // RUN: %clang_analyze_cc1 %s \
// RUN: -analyzer-checker=debug.DumpDominators \ // RUN: -analyzer-checker=debug.DumpDominators \
// RUN: -analyzer-checker=debug.DumpPostDominators \ // RUN: -analyzer-checker=debug.DumpPostDominators \
// RUN: -analyzer-checker=debug.DumpControlDependencies \
// RUN: 2>&1 | FileCheck %s // RUN: 2>&1 | FileCheck %s
bool coin(); bool coin();
@ -20,7 +21,8 @@ void f() {
// [B3 (ENTRY)] -> [B1] -> [B2] -> [B0 (EXIT)] // [B3 (ENTRY)] -> [B1] -> [B2] -> [B0 (EXIT)]
// CHECK: Immediate dominance tree (Node#,IDom#): // CHECK: Control dependencies (Node#,Dependency#):
// CHECK-NEXT: Immediate dominance tree (Node#,IDom#):
// CHECK-NEXT: (0,2) // CHECK-NEXT: (0,2)
// CHECK-NEXT: (1,3) // CHECK-NEXT: (1,3)
// CHECK-NEXT: (2,1) // CHECK-NEXT: (2,1)
@ -42,13 +44,18 @@ void funcWithBranch() {
} }
} }
// ----> [B2] ----> // 1st if 2nd if
// / \ // [B5 (ENTRY)] -> [B4] -> [B3] -> [B2] -> [B1] -> [B0 (EXIT)]
// [B5 (ENTRY)] -> [B4] -> [B3] -----------> [B1] // \ \ / /
// \ / // \ -------------> /
// ----> [B0 (EXIT)] <---- // ------------------------------>
// CHECK: Immediate dominance tree (Node#,IDom#): // CHECK: Control dependencies (Node#,Dependency#):
// CHECK-NEXT: (1,4)
// CHECK-NEXT: (2,3)
// CHECK-NEXT: (2,4)
// CHECK-NEXT: (3,4)
// CHECK-NEXT: Immediate dominance tree (Node#,IDom#):
// CHECK-NEXT: (0,4) // CHECK-NEXT: (0,4)
// CHECK-NEXT: (1,3) // CHECK-NEXT: (1,3)
// CHECK-NEXT: (2,3) // CHECK-NEXT: (2,3)

91
clang/unittests/Analysis/CFGDominatorTree.cpp
View File

@ -98,6 +98,97 @@ TEST(CFGDominatorTree, DomTree) {
EXPECT_TRUE(PostDom.dominates(nullptr, ExitBlock)); EXPECT_TRUE(PostDom.dominates(nullptr, ExitBlock));
} }
TEST(CFGDominatorTree, ControlDependency) {
const char *Code = R"(bool coin();
void funcWithBranch() {
int x = 0;
if (coin()) {
if (coin()) {
x = 5;
}
int j = 10 / x;
(void)j;
}
};)";
BuildResult Result = BuildCFG(Code);
EXPECT_EQ(BuildResult::BuiltCFG, Result.getStatus());
// 1st if 2nd if
// [B5 (ENTRY)] -> [B4] -> [B3] -> [B2] -> [B1] -> [B0 (EXIT)]
// \ \ / /
// \ -------------> /
// ------------------------------>
CFG *cfg = Result.getCFG();
// Sanity checks.
EXPECT_EQ(cfg->size(), 6u);
CFGBlock *ExitBlock = *cfg->begin();
EXPECT_EQ(ExitBlock, &cfg->getExit());
CFGBlock *NullDerefBlock = *(cfg->begin() + 1);
CFGBlock *SecondThenBlock = *(cfg->begin() + 2);
CFGBlock *SecondIfBlock = *(cfg->begin() + 3);
CFGBlock *FirstIfBlock = *(cfg->begin() + 4);
CFGBlock *EntryBlock = *(cfg->begin() + 5);
EXPECT_EQ(EntryBlock, &cfg->getEntry());
ControlDependencyCalculator Control(cfg);
EXPECT_TRUE(Control.isControlDependent(SecondThenBlock, SecondIfBlock));
EXPECT_TRUE(Control.isControlDependent(SecondIfBlock, FirstIfBlock));
EXPECT_FALSE(Control.isControlDependent(NullDerefBlock, SecondIfBlock));
}
TEST(CFGDominatorTree, ControlDependencyWithLoops) {
const char *Code = R"(int test3() {
int x,y,z;
x = y = z = 1;
if (x > 0) {
while (x >= 0){
while (y >= x) {
x = x-1;
y = y/2;
}
}
}
z = y;
return 0;
})";
BuildResult Result = BuildCFG(Code);
EXPECT_EQ(BuildResult::BuiltCFG, Result.getStatus());
// <- [B2] <-
// / \
// [B8 (ENTRY)] -> [B7] -> [B6] ---> [B5] -> [B4] -> [B3]
// \ | \ /
// \ | <-------------
// \ \
// --------> [B1] -> [B0 (EXIT)]
CFG *cfg = Result.getCFG();
ControlDependencyCalculator Control(cfg);
auto GetBlock = [cfg] (unsigned Index) -> CFGBlock * {
assert(Index < cfg->size());
return *(cfg->begin() + Index);
};
// While not immediately obvious, the second block in fact post dominates the
// fifth, hence B5 is not a control dependency of 2.
EXPECT_FALSE(Control.isControlDependent(GetBlock(5), GetBlock(2)));
}
} // namespace } // namespace
} // namespace analysis } // namespace analysis
} // namespace clang } // namespace clang