tekknolagi updated this revision to Diff 171568.
tekknolagi added a comment.
Skip non-definitions in `VisitRecord`
Repository:
rC Clang
https://reviews.llvm.org/D53206
Files:
lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
test/Analysis/padding_inherit.cpp
Index: test/Analysis/padding_inherit.cpp
===================================================================
--- /dev/null
+++ test/Analysis/padding_inherit.cpp
@@ -0,0 +1,28 @@
+// RUN: %clang_analyze_cc1 -std=c++14 -analyzer-checker=optin.performance -analyzer-config optin.performance.Padding:AllowedPad=20 -verify %s
+
+// A class that has no fields and one base class should visit that base class
+// instead. Note that despite having excess padding of 2, this is flagged
+// because of its usage in an array of 100 elements below (`ais').
+// TODO: Add a note to the bug report with BugReport::addNote() to mention the
+// variable using the class and also mention what class is inherting from what.
+// expected-warning@+1{{Excessive padding in 'struct FakeIntSandwich'}}
+struct FakeIntSandwich {
+ char c1;
+ int i;
+ char c2;
+};
+
+struct AnotherIntSandwich : FakeIntSandwich { // no-warning
+};
+
+// But we don't yet support multiple base classes.
+struct IntSandwich {};
+struct TooManyBaseClasses : FakeIntSandwich, IntSandwich { // no-warning
+};
+
+AnotherIntSandwich ais[100];
+
+struct Empty {};
+struct DoubleEmpty : Empty { // no-warning
+ Empty e;
+};
Index: lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
===================================================================
--- lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
+++ lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
@@ -75,6 +75,20 @@
if (shouldSkipDecl(RD))
return;
+ // TODO: Figure out why we are going through declarations and not only
+ // definitions.
+ if (!(RD = RD->getDefinition()))
+ return;
+
+ // This is the simplest correct case: a class with no fields and one base
+ // class. Other cases are more complicated because of how the base classes
+ // & fields might interact, so we don't bother dealing with them.
+ // TODO: Support other combinations of base classes and fields.
+ if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD))
+ if (CXXRD->field_empty() && CXXRD->getNumBases() == 1)
+ return visitRecord(CXXRD->bases().begin()->getType()->getAsRecordDecl(),
+ PadMultiplier);
+
auto &ASTContext = RD->getASTContext();
const ASTRecordLayout &RL = ASTContext.getASTRecordLayout(RD);
assert(llvm::isPowerOf2_64(RL.getAlignment().getQuantity()));
@@ -112,12 +126,15 @@
if (RT == nullptr)
return;
- // TODO: Recurse into the fields and base classes to see if any
- // of those have excess padding.
+ // TODO: Recurse into the fields to see if they have excess padding.
visitRecord(RT->getDecl(), Elts);
}
bool shouldSkipDecl(const RecordDecl *RD) const {
+ // TODO: Figure out why we are going through declarations and not only
+ // definitions.
+ if (!(RD = RD->getDefinition()))
+ return true;
auto Location = RD->getLocation();
// If the construct doesn't have a source file, then it's not something
// we want to diagnose.
@@ -132,13 +149,14 @@
// Not going to attempt to optimize unions.
if (RD->isUnion())
return true;
- // How do you reorder fields if you haven't got any?
- if (RD->field_empty())
- return true;
if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
// Tail padding with base classes ends up being very complicated.
- // We will skip objects with base classes for now.
- if (CXXRD->getNumBases() != 0)
+ // We will skip objects with base classes for now, unless they do not
+ // have fields.
+ // TODO: Handle more base class scenarios.
+ if (!CXXRD->field_empty() && CXXRD->getNumBases() != 0)
+ return true;
+ if (CXXRD->field_empty() && CXXRD->getNumBases() != 1)
return true;
// Virtual bases are complicated, skipping those for now.
if (CXXRD->getNumVBases() != 0)
@@ -150,6 +168,10 @@
if (CXXRD->getTypeForDecl()->isInstantiationDependentType())
return true;
}
+ // How do you reorder fields if you haven't got any?
+ else if (RD->field_empty())
+ return true;
+
auto IsTrickyField = [](const FieldDecl *FD) -> bool {
// Bitfield layout is hard.
if (FD->isBitField())
@@ -323,7 +345,7 @@
BR->emitReport(std::move(Report));
}
};
-}
+} // namespace
void ento::registerPaddingChecker(CheckerManager &Mgr) {
Mgr.registerChecker<PaddingChecker>();
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