[StaticAnalyzer] Completely unrolling specific loops with known bound option

This feature allows the analyzer to consider loops to completely unroll.
New requirements/rules (for unrolling) can be added easily via ASTMatchers.

Right now it is hidden behind a flag, the aim is to find the correct heuristic
and create a solution which results higher coverage % and more precise
analysis, thus can be enabled by default.

Right now the blocks which belong to an unrolled loop are marked by the
LoopVisitor which adds them to the ProgramState.
Then whenever we encounter a CFGBlock in the processCFGBlockEntrance which is
marked then we skip its investigating. That means, it won't be considered to
be visited more than the maximal bound for visiting since it won't be checked.

llvm-svn: 309006

1 files changed, 207 insertions, 0 deletions

diff --git a/clang/lib/StaticAnalyzer/Core/LoopUnrolling.cpp b/clang/lib/StaticAnalyzer/Core/LoopUnrolling.cpp
new file mode 100644
index 00000000000..a88e0622f11
--- /dev/null
+++ b/clang/lib/StaticAnalyzer/Core/LoopUnrolling.cpp
@@ -0,0 +1,207 @@
+//===--- LoopUnrolling.cpp - Unroll loops -----------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// This file contains functions which are used to decide if a loop worth to be
+/// unrolled. Moreover contains function which mark the CFGBlocks which belongs
+/// to the unrolled loop and store them in ProgramState.
+///
+//===----------------------------------------------------------------------===//
+
+#include "clang/Analysis/CFGStmtMap.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/AST/ParentMap.h"
+#include "clang/AST/StmtVisitor.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/LoopUnrolling.h"
+#include "llvm/ADT/Statistic.h"
+
+using namespace clang;
+using namespace ento;
+using namespace clang::ast_matchers;
+
+#define DEBUG_TYPE "LoopUnrolling"
+
+STATISTIC(NumTimesLoopUnrolled,
+          "The # of times a loop has got completely unrolled");
+
+REGISTER_MAP_WITH_PROGRAMSTATE(UnrolledLoops, const Stmt *,
+                               const FunctionDecl *)
+
+namespace clang {
+namespace ento {
+
+static bool isLoopStmt(const Stmt *S) {
+  return S && (isa<ForStmt>(S) || isa<WhileStmt>(S) || isa<DoStmt>(S));
+}
+
+static internal::Matcher<Stmt> simpleCondition(StringRef BindName) {
+  return binaryOperator(
+      anyOf(hasOperatorName("<"), hasOperatorName(">"), hasOperatorName("<="),
+            hasOperatorName(">="), hasOperatorName("!=")),
+      hasEitherOperand(ignoringParenImpCasts(
+          declRefExpr(to(varDecl(hasType(isInteger())).bind(BindName))))),
+      hasEitherOperand(ignoringParenImpCasts(integerLiteral())));
+}
+
+static internal::Matcher<Stmt> changeIntBoundNode(StringRef NodeName) {
+  return anyOf(hasDescendant(unaryOperator(
+                   anyOf(hasOperatorName("--"), hasOperatorName("++")),
+                   hasUnaryOperand(ignoringParenImpCasts(
+                       declRefExpr(to(varDecl(equalsBoundNode(NodeName)))))))),
+               hasDescendant(binaryOperator(
+                   anyOf(hasOperatorName("="), hasOperatorName("+="),
+                         hasOperatorName("/="), hasOperatorName("*="),
+                         hasOperatorName("-=")),
+                   hasLHS(ignoringParenImpCasts(
+                       declRefExpr(to(varDecl(equalsBoundNode(NodeName)))))))));
+}
+
+static internal::Matcher<Stmt> callByRef(StringRef NodeName) {
+  return hasDescendant(callExpr(forEachArgumentWithParam(
+      declRefExpr(to(varDecl(equalsBoundNode(NodeName)))),
+      parmVarDecl(hasType(references(qualType(unless(isConstQualified()))))))));
+}
+
+static internal::Matcher<Stmt> assignedToRef(StringRef NodeName) {
+  return hasDescendant(varDecl(
+      allOf(hasType(referenceType()),
+            hasInitializer(
+                anyOf(initListExpr(has(
+                          declRefExpr(to(varDecl(equalsBoundNode(NodeName)))))),
+                      declRefExpr(to(varDecl(equalsBoundNode(NodeName)))))))));
+}
+
+static internal::Matcher<Stmt> getAddrTo(StringRef NodeName) {
+  return hasDescendant(unaryOperator(
+      hasOperatorName("&"),
+      hasUnaryOperand(declRefExpr(hasDeclaration(equalsBoundNode(NodeName))))));
+}
+
+static internal::Matcher<Stmt> hasSuspiciousStmt(StringRef NodeName) {
+  return anyOf(hasDescendant(gotoStmt()), hasDescendant(switchStmt()),
+               // Escaping and not known mutation of the loop counter is handled
+               // by exclusion of assigning and address-of operators and
+               // pass-by-ref function calls on the loop counter from the body.
+               changeIntBoundNode(NodeName), callByRef(NodeName),
+               getAddrTo(NodeName), assignedToRef(NodeName));
+}
+
+static internal::Matcher<Stmt> forLoopMatcher() {
+  return forStmt(
+             hasCondition(simpleCondition("initVarName")),
+             // Initialization should match the form: 'int i = 6' or 'i = 42'.
+             hasLoopInit(
+                 anyOf(declStmt(hasSingleDecl(
+                           varDecl(allOf(hasInitializer(integerLiteral()),
+                                         equalsBoundNode("initVarName"))))),
+                       binaryOperator(hasLHS(declRefExpr(to(varDecl(
+                                          equalsBoundNode("initVarName"))))),
+                                      hasRHS(integerLiteral())))),
+             // Incrementation should be a simple increment or decrement
+             // operator call.
+             hasIncrement(unaryOperator(
+                 anyOf(hasOperatorName("++"), hasOperatorName("--")),
+                 hasUnaryOperand(declRefExpr(
+                     to(varDecl(allOf(equalsBoundNode("initVarName"),
+                                      hasType(isInteger())))))))),
+             unless(hasBody(hasSuspiciousStmt("initVarName")))).bind("forLoop");
+}
+
+bool shouldCompletelyUnroll(const Stmt *LoopStmt, ASTContext &ASTCtx) {
+
+  if (!isLoopStmt(LoopStmt))
+    return false;
+
+  // TODO: Match the cases where the bound is not a concrete literal but an
+  // integer with known value
+
+  auto Matches = match(forLoopMatcher(), *LoopStmt, ASTCtx);
+  return !Matches.empty();
+}
+
+namespace {
+class LoopBlockVisitor : public ConstStmtVisitor<LoopBlockVisitor> {
+public:
+  LoopBlockVisitor(llvm::SmallPtrSet<const CFGBlock *, 8> &BS) : BlockSet(BS) {}
+
+  void VisitChildren(const Stmt *S) {
+    for (const Stmt *Child : S->children())
+      if (Child)
+        Visit(Child);
+  }
+
+  void VisitStmt(const Stmt *S) {
+    // In case of nested loops we only unroll the inner loop if it's marked too.
+    if (!S || (isLoopStmt(S) && S != LoopStmt))
+      return;
+    BlockSet.insert(StmtToBlockMap->getBlock(S));
+    VisitChildren(S);
+  }
+
+  void setBlocksOfLoop(const Stmt *Loop, const CFGStmtMap *M) {
+    BlockSet.clear();
+    StmtToBlockMap = M;
+    LoopStmt = Loop;
+    Visit(LoopStmt);
+  }
+
+private:
+  llvm::SmallPtrSet<const CFGBlock *, 8> &BlockSet;
+  const CFGStmtMap *StmtToBlockMap;
+  const Stmt *LoopStmt;
+};
+}
+// TODO: refactor this function using LoopExit CFG element - once we have the
+// information when the simulation reaches the end of the loop we can cleanup
+// the state
+bool isUnrolledLoopBlock(const CFGBlock *Block, ExplodedNode *Pred,
+                         AnalysisManager &AMgr) {
+  const Stmt *Term = Block->getTerminator();
+  auto State = Pred->getState();
+  // In case of nested loops in an inlined function should not be unrolled only
+  // if the inner loop is marked.
+  if (Term && isLoopStmt(Term) && !State->contains<UnrolledLoops>(Term))
+    return false;
+
+  const CFGBlock *SearchedBlock;
+  llvm::SmallPtrSet<const CFGBlock *, 8> BlockSet;
+  LoopBlockVisitor LBV(BlockSet);
+  // Check the CFGBlocks of every marked loop.
+  for (auto &E : State->get<UnrolledLoops>()) {
+    SearchedBlock = Block;
+    const StackFrameContext *StackFrame = Pred->getStackFrame();
+    ParentMap PM(E.second->getBody());
+    CFGStmtMap *M = CFGStmtMap::Build(AMgr.getCFG(E.second), &PM);
+    LBV.setBlocksOfLoop(E.first, M);
+    // In case of an inlined function call check if any of its callSiteBlock is
+    // marked.
+    while (SearchedBlock && BlockSet.find(SearchedBlock) == BlockSet.end()) {
+      SearchedBlock = StackFrame->getCallSiteBlock();
+      StackFrame = StackFrame->getParent()->getCurrentStackFrame();
+    }
+    delete M;
+    if (SearchedBlock)
+      return true;
+  }
+  return false;
+}
+
+ProgramStateRef markLoopAsUnrolled(const Stmt *Term, ProgramStateRef State,
+                                   const FunctionDecl *FD) {
+  if (State->contains<UnrolledLoops>(Term))
+    return State;
+
+  State = State->set<UnrolledLoops>(Term, FD);
+  ++NumTimesLoopUnrolled;
+  return State;
+}
+}
+}