[clang] 4950198 - [clang][dataflow] Add multi-variable constant propagation example.
Yitzhak Mandelbaum via cfe-commits
cfe-commits at lists.llvm.org
Tue Jan 4 06:29:07 PST 2022
Author: Yitzhak Mandelbaum
Date: 2022-01-04T14:28:23Z
New Revision: 4950198116a5b243b8e7b4267e0397e118a27c43
URL: https://github.com/llvm/llvm-project/commit/4950198116a5b243b8e7b4267e0397e118a27c43
DIFF: https://github.com/llvm/llvm-project/commit/4950198116a5b243b8e7b4267e0397e118a27c43.diff
LOG: [clang][dataflow] Add multi-variable constant propagation example.
Adds another constant-propagation analysis that covers all variables in
the scope (vs the existing single-variable demo). But, the analysis is still
unsuited to use, in that ignores issues of escaping variables.
Differential Revision: https://reviews.llvm.org/D116370
Added:
clang/unittests/Analysis/FlowSensitive/MultiVarConstantPropagationTest.cpp
Modified:
clang/unittests/Analysis/FlowSensitive/CMakeLists.txt
Removed:
################################################################################
diff --git a/clang/unittests/Analysis/FlowSensitive/CMakeLists.txt b/clang/unittests/Analysis/FlowSensitive/CMakeLists.txt
index 753cf486953e..414f5c8810c7 100644
--- a/clang/unittests/Analysis/FlowSensitive/CMakeLists.txt
+++ b/clang/unittests/Analysis/FlowSensitive/CMakeLists.txt
@@ -5,6 +5,7 @@ set(LLVM_LINK_COMPONENTS
add_clang_unittest(ClangAnalysisFlowSensitiveTests
MapLatticeTest.cpp
+ MultiVarConstantPropagationTest.cpp
SingleVarConstantPropagationTest.cpp
TestingSupport.cpp
TestingSupportTest.cpp
diff --git a/clang/unittests/Analysis/FlowSensitive/MultiVarConstantPropagationTest.cpp b/clang/unittests/Analysis/FlowSensitive/MultiVarConstantPropagationTest.cpp
new file mode 100644
index 000000000000..c5b792a64d55
--- /dev/null
+++ b/clang/unittests/Analysis/FlowSensitive/MultiVarConstantPropagationTest.cpp
@@ -0,0 +1,486 @@
+//===- unittests/Analysis/FlowSensitive/SingelVarConstantPropagation.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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines a simplistic version of Constant Propagation as an example
+// of a forward, monotonic dataflow analysis. The analysis tracks all
+// variables in the scope, but lacks escape analysis.
+//
+//===----------------------------------------------------------------------===//
+
+#include "TestingSupport.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/Stmt.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Analysis/FlowSensitive/DataflowAnalysis.h"
+#include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
+#include "clang/Analysis/FlowSensitive/DataflowLattice.h"
+#include "clang/Analysis/FlowSensitive/MapLattice.h"
+#include "clang/Tooling/Tooling.h"
+#include "llvm/ADT/None.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Testing/Support/Annotations.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include <cstdint>
+#include <memory>
+#include <ostream>
+#include <string>
+#include <utility>
+
+namespace clang {
+namespace dataflow {
+namespace {
+using namespace ast_matchers;
+
+// Models the value of an expression at a program point, for all paths through
+// the program.
+struct ValueLattice {
+ // FIXME: change the internal representation to use a `std::variant`, once
+ // clang admits C++17 constructs.
+ enum class ValueState : bool {
+ Undefined,
+ Defined,
+ };
+ // `State` determines the meaning of the lattice when `Value` is `None`:
+ // * `Undefined` -> bottom,
+ // * `Defined` -> top.
+ ValueState State;
+
+ // When `None`, the lattice is either at top or bottom, based on `State`.
+ llvm::Optional<int64_t> Value;
+
+ constexpr ValueLattice() : State(ValueState::Undefined), Value(llvm::None) {}
+ constexpr ValueLattice(int64_t V) : State(ValueState::Defined), Value(V) {}
+ constexpr ValueLattice(ValueState S) : State(S), Value(llvm::None) {}
+
+ static constexpr ValueLattice bottom() {
+ return ValueLattice(ValueState::Undefined);
+ }
+ static constexpr ValueLattice top() {
+ return ValueLattice(ValueState::Defined);
+ }
+
+ friend bool operator==(const ValueLattice &Lhs, const ValueLattice &Rhs) {
+ return Lhs.State == Rhs.State && Lhs.Value == Rhs.Value;
+ }
+ friend bool operator!=(const ValueLattice &Lhs, const ValueLattice &Rhs) {
+ return !(Lhs == Rhs);
+ }
+
+ LatticeJoinEffect join(const ValueLattice &Other) {
+ if (*this == Other || Other == bottom() || *this == top())
+ return LatticeJoinEffect::Unchanged;
+
+ if (*this == bottom()) {
+ *this = Other;
+ return LatticeJoinEffect::Changed;
+ }
+
+ *this = top();
+ return LatticeJoinEffect::Changed;
+ }
+};
+
+std::ostream &operator<<(std::ostream &OS, const ValueLattice &L) {
+ if (L.Value.hasValue())
+ return OS << *L.Value;
+ switch (L.State) {
+ case ValueLattice::ValueState::Undefined:
+ return OS << "None";
+ case ValueLattice::ValueState::Defined:
+ return OS << "Any";
+ }
+}
+
+using ConstantPropagationLattice = VarMapLattice<ValueLattice>;
+
+constexpr char kDecl[] = "decl";
+constexpr char kVar[] = "var";
+constexpr char kInit[] = "init";
+constexpr char kJustAssignment[] = "just-assignment";
+constexpr char kAssignment[] = "assignment";
+constexpr char kRHS[] = "rhs";
+
+auto refToVar() { return declRefExpr(to(varDecl().bind(kVar))); }
+
+// N.B. This analysis is deliberately simplistic, leaving out many important
+// details needed for a real analysis. Most notably, the transfer function does
+// not account for the variable's address possibly escaping, which would
+// invalidate the analysis. It also could be optimized to drop out-of-scope
+// variables from the map.
+class ConstantPropagationAnalysis
+ : public DataflowAnalysis<ConstantPropagationAnalysis,
+ ConstantPropagationLattice> {
+public:
+ explicit ConstantPropagationAnalysis(ASTContext &Context)
+ : DataflowAnalysis<ConstantPropagationAnalysis,
+ ConstantPropagationLattice>(Context) {}
+
+ static ConstantPropagationLattice initialElement() {
+ return ConstantPropagationLattice::bottom();
+ }
+
+ ConstantPropagationLattice
+ transfer(const Stmt *S, ConstantPropagationLattice Vars, Environment &Env) {
+ auto matcher =
+ stmt(anyOf(declStmt(hasSingleDecl(
+ varDecl(decl().bind(kVar), hasType(isInteger()),
+ optionally(hasInitializer(expr().bind(kInit))))
+ .bind(kDecl))),
+ binaryOperator(hasOperatorName("="), hasLHS(refToVar()),
+ hasRHS(expr().bind(kRHS)))
+ .bind(kJustAssignment),
+ binaryOperator(isAssignmentOperator(), hasLHS(refToVar()))
+ .bind(kAssignment)));
+
+ ASTContext &Context = getASTContext();
+ auto Results = match(matcher, *S, Context);
+ if (Results.empty())
+ return Vars;
+ const BoundNodes &Nodes = Results[0];
+
+ const auto *Var = Nodes.getNodeAs<clang::VarDecl>(kVar);
+ assert(Var != nullptr);
+
+ if (Nodes.getNodeAs<clang::VarDecl>(kDecl) != nullptr) {
+ if (const auto *E = Nodes.getNodeAs<clang::Expr>(kInit)) {
+ Expr::EvalResult R;
+ Vars[Var] = (E->EvaluateAsInt(R, Context) && R.Val.isInt())
+ ? ValueLattice(R.Val.getInt().getExtValue())
+ : ValueLattice::top();
+ } else {
+ // An unitialized variable holds *some* value, but we don't know what it
+ // is (it is implementation defined), so we set it to top.
+ Vars[Var] = ValueLattice::top();
+ }
+ return Vars;
+ }
+
+ if (Nodes.getNodeAs<clang::Expr>(kJustAssignment)) {
+ const auto *E = Nodes.getNodeAs<clang::Expr>(kRHS);
+ assert(E != nullptr);
+
+ Expr::EvalResult R;
+ Vars[Var] = (E->EvaluateAsInt(R, Context) && R.Val.isInt())
+ ? ValueLattice(R.Val.getInt().getExtValue())
+ : ValueLattice::top();
+ return Vars;
+ }
+
+ // Any assignment involving the expression itself resets the variable to
+ // "unknown". A more advanced analysis could try to evaluate the compound
+ // assignment. For example, `x += 0` need not invalidate `x`.
+ if (Nodes.getNodeAs<clang::Expr>(kAssignment)) {
+ Vars[Var] = ValueLattice::top();
+ return Vars;
+ }
+
+ llvm_unreachable("expected at least one bound identifier");
+ }
+};
+
+using ::testing::IsEmpty;
+using ::testing::Pair;
+using ::testing::UnorderedElementsAre;
+
+MATCHER_P(Var, name,
+ (llvm::Twine(negation ? "isn't" : "is") + " a variable named `" +
+ name + "`")
+ .str()) {
+ return arg->getName() == name;
+}
+
+MATCHER_P(HasConstantVal, v, "") {
+ return arg.Value.hasValue() && *arg.Value == v;
+}
+
+MATCHER(Varies, "") { return arg == arg.top(); }
+
+MATCHER_P(HoldsCPLattice, m,
+ ((negation ? "doesn't hold" : "holds") +
+ llvm::StringRef(" a lattice element that ") +
+ ::testing::DescribeMatcher<ConstantPropagationLattice>(m, negation))
+ .str()) {
+ return ExplainMatchResult(m, arg.Lattice, result_listener);
+}
+
+class MultiVarConstantPropagationTest : public ::testing::Test {
+protected:
+ template <typename Matcher>
+ void RunDataflow(llvm::StringRef Code, Matcher Expectations) {
+ test::checkDataflow<ConstantPropagationAnalysis>(
+ Code, "fun",
+ [](ASTContext &C, Environment &) {
+ return ConstantPropagationAnalysis(C);
+ },
+ [&Expectations](
+ llvm::ArrayRef<std::pair<
+ std::string,
+ DataflowAnalysisState<ConstantPropagationAnalysis::Lattice>>>
+ Results,
+ ASTContext &) { EXPECT_THAT(Results, Expectations); },
+ {"-fsyntax-only", "-std=c++17"});
+ }
+};
+
+TEST_F(MultiVarConstantPropagationTest, JustInit) {
+ std::string Code = R"(
+ void fun() {
+ int target = 1;
+ // [[p]]
+ }
+ )";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1)))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, Assignment) {
+ std::string Code = R"(
+ void fun() {
+ int target = 1;
+ // [[p1]]
+ target = 2;
+ // [[p2]]
+ }
+ )";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1))))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(2)))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, AssignmentCall) {
+ std::string Code = R"(
+ int g();
+ void fun() {
+ int target;
+ target = g();
+ // [[p]]
+ }
+ )";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies()))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, AssignmentBinOp) {
+ std::string Code = R"(
+ void fun() {
+ int target;
+ target = 2 + 3;
+ // [[p]]
+ }
+ )";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(5)))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, PlusAssignment) {
+ std::string Code = R"(
+ void fun() {
+ int target = 1;
+ // [[p1]]
+ target += 2;
+ // [[p2]]
+ }
+ )";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1))))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies()))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, SameAssignmentInBranches) {
+ std::string Code = R"cc(
+ void fun(bool b) {
+ int target;
+ // [[p1]]
+ if (b) {
+ target = 2;
+ // [[pT]]
+ } else {
+ target = 2;
+ // [[pF]]
+ }
+ (void)0;
+ // [[p2]]
+ }
+ )cc";
+ RunDataflow(Code,
+ UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies())))),
+ Pair("pT", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), HasConstantVal(2))))),
+ Pair("pF", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), HasConstantVal(2))))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), HasConstantVal(2)))))));
+}
+
+// Verifies that the analysis tracks multiple variables simultaneously.
+TEST_F(MultiVarConstantPropagationTest, TwoVariables) {
+ std::string Code = R"(
+ void fun() {
+ int target = 1;
+ // [[p1]]
+ int other = 2;
+ // [[p2]]
+ target = 3;
+ // [[p3]]
+ }
+ )";
+ RunDataflow(Code,
+ UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), HasConstantVal(1))))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), HasConstantVal(1)),
+ Pair(Var("other"), HasConstantVal(2))))),
+ Pair("p3", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), HasConstantVal(3)),
+ Pair(Var("other"), HasConstantVal(2)))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, TwoVariablesInBranches) {
+ std::string Code = R"cc(
+ void fun(bool b) {
+ int target;
+ int other;
+ // [[p1]]
+ if (b) {
+ target = 2;
+ // [[pT]]
+ } else {
+ other = 3;
+ // [[pF]]
+ }
+ (void)0;
+ // [[p2]]
+ }
+ )cc";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies()),
+ Pair(Var("other"), Varies())))),
+ Pair("pT", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), HasConstantVal(2)),
+ Pair(Var("other"), Varies())))),
+ Pair("pF", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("other"), HasConstantVal(3)),
+ Pair(Var("target"), Varies())))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies()),
+ Pair(Var("other"), Varies()))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, SameAssignmentInBranch) {
+ std::string Code = R"cc(
+ void fun(bool b) {
+ int target = 1;
+ // [[p1]]
+ if (b) {
+ target = 1;
+ }
+ (void)0;
+ // [[p2]]
+ }
+ )cc";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1))))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1)))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, NewVarInBranch) {
+ std::string Code = R"cc(
+ void fun(bool b) {
+ if (b) {
+ int target;
+ // [[p1]]
+ target = 1;
+ // [[p2]]
+ } else {
+ int target;
+ // [[p3]]
+ target = 1;
+ // [[p4]]
+ }
+ }
+ )cc";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies())))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1))))),
+ Pair("p3", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies())))),
+ Pair("p4", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1)))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, DifferentAssignmentInBranches) {
+ std::string Code = R"cc(
+ void fun(bool b) {
+ int target;
+ // [[p1]]
+ if (b) {
+ target = 1;
+ // [[pT]]
+ } else {
+ target = 2;
+ // [[pF]]
+ }
+ (void)0;
+ // [[p2]]
+ }
+ )cc";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies())))),
+ Pair("pT", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1))))),
+ Pair("pF", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(2))))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies()))))));
+}
+
+TEST_F(MultiVarConstantPropagationTest, DifferentAssignmentInBranch) {
+ std::string Code = R"cc(
+ void fun(bool b) {
+ int target = 1;
+ // [[p1]]
+ if (b) {
+ target = 3;
+ }
+ (void)0;
+ // [[p2]]
+ }
+ )cc";
+ RunDataflow(Code, UnorderedElementsAre(
+ Pair("p1", HoldsCPLattice(UnorderedElementsAre(Pair(
+ Var("target"), HasConstantVal(1))))),
+ Pair("p2", HoldsCPLattice(UnorderedElementsAre(
+ Pair(Var("target"), Varies()))))));
+}
+
+} // namespace
+} // namespace dataflow
+} // namespace clang
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