bcraig updated this revision to Diff 42524.
bcraig marked 3 inline comments as done.
bcraig added a comment.
Anna Zaks last round of review requests.
http://reviews.llvm.org/D14779
Files:
lib/StaticAnalyzer/Checkers/CMakeLists.txt
lib/StaticAnalyzer/Checkers/Checkers.td
lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
test/Analysis/padding_c.c
test/Analysis/padding_cpp.cpp
test/Analysis/padding_message.cpp
Index: test/Analysis/padding_message.cpp
===================================================================
--- /dev/null
+++ test/Analysis/padding_message.cpp
@@ -0,0 +1,185 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux -std=c++14 -analyze -analyzer-checker=performance -analyzer-config performance.Padding:AllowedPad=2 -verify %s
+
+// expected-warning@+1{{Excessive padding in 'struct IntSandwich' (6 padding bytes, where 2 is optimal)}}
+struct IntSandwich {
+ char c1;
+ int i;
+ char c2;
+};
+
+// expected-warning@+1{{Excessive padding in 'struct TurDuckHen' (6 padding bytes, where 2 is optimal)}}
+struct TurDuckHen {
+ char c1;
+ struct IntSandwich i;
+ char c2;
+};
+
+#pragma pack(push)
+#pragma pack(2)
+// expected-warning@+1{{Excessive padding in 'struct SmallIntSandwich' (4 padding bytes, where 0 is optimal)}}
+struct SmallIntSandwich {
+ char c1;
+ int i1;
+ char c2;
+ int i2;
+ char c3;
+ int i3;
+ char c4;
+};
+#pragma pack(pop)
+
+union SomeUnion { // no-warning
+ char c;
+ short s;
+ int i;
+};
+
+// expected-warning@+1{{Excessive padding in 'struct HoldsAUnion' (6 padding bytes, where 2 is optimal)}}
+struct HoldsAUnion {
+ char c1;
+ union SomeUnion u;
+ char c2;
+};
+
+struct SmallCharArray { // no-warning
+ char c[5];
+};
+
+struct MediumIntArray { // no-warning
+ int i[5];
+};
+
+// expected-warning@+1{{Excessive padding in 'struct StructSandwich' (6 padding bytes, where 2 is optimal)}}
+struct StructSandwich {
+ struct SmallCharArray s;
+ struct MediumIntArray m;
+ struct SmallCharArray s2;
+};
+
+// expected-warning@+1{{Excessive padding in 'TypedefSandwich' (6 padding bytes, where 2 is optimal)}}
+typedef struct {
+ char c1;
+ int i;
+ char c2;
+} TypedefSandwich;
+
+// expected-warning@+1{{Excessive padding in 'struct StructAttrAlign' (10 padding bytes, where 2 is optimal)}}
+struct StructAttrAlign {
+ char c1;
+ int i;
+ char c2;
+} __attribute__((aligned(8)));
+
+// expected-warning@+1{{Excessive padding in 'struct OverlyAlignedChar' (8185 padding bytes, where 4089 is optimal)}}
+struct OverlyAlignedChar {
+ char c1;
+ int x;
+ char c2;
+ char c __attribute__((aligned(4096)));
+};
+
+// expected-warning@+1{{Excessive padding in 'struct HoldsOverlyAlignedChar' (8190 padding bytes, where 4094 is optimal)}}
+struct HoldsOverlyAlignedChar {
+ char c1;
+ struct OverlyAlignedChar o;
+ char c2;
+};
+
+void internalStructFunc() {
+ // expected-warning@+1{{Excessive padding in 'struct X' (6 padding bytes, where 2 is optimal)}}
+ struct X {
+ char c1;
+ int t;
+ char c2;
+ };
+ struct X obj;
+}
+
+void typedefStructFunc() {
+ // expected-warning@+1{{Excessive padding in 'S' (6 padding bytes, where 2 is optimal)}}
+ typedef struct {
+ char c1;
+ int t;
+ char c2;
+ } S;
+ S obj;
+}
+
+// expected-warning@+1{{Excessive padding in 'struct DefaultAttrAlign' (22 padding bytes, where 6 is optimal)}}
+struct DefaultAttrAlign {
+ char c1;
+ long long i;
+ char c2;
+} __attribute__((aligned));
+
+// expected-warning@+1{{Excessive padding in 'struct SmallArrayShortSandwich' (2 padding bytes, where 0 is optimal)}}
+struct SmallArrayShortSandwich {
+ char c1;
+ short s;
+ char c2;
+} ShortArray[20];
+
+// expected-warning@+1{{Excessive padding in 'struct SmallArrayInFunc' (2 padding bytes, where 0 is optimal)}}
+struct SmallArrayInFunc {
+ char c1;
+ short s;
+ char c2;
+};
+
+void arrayHolder() {
+ struct SmallArrayInFunc Arr[15];
+}
+
+// expected-warning@+1{{Excessive padding in 'class VirtualIntSandwich' (10 padding bytes, where 2 is optimal)}}
+class VirtualIntSandwich {
+ virtual void foo() {}
+ char c1;
+ int i;
+ char c2;
+};
+
+// constructed so as not to have tail padding
+// expected-warning@+1{{Excessive padding in 'class InnerPaddedB' (6 padding bytes, where 2 is optimal)}}
+class InnerPaddedB {
+ char c1;
+ int i1;
+ char c2;
+ int i2;
+};
+
+class Empty {}; // no-warning
+
+// expected-warning@+1{{Excessive padding in 'class LotsOfSpace' (6 padding bytes, where 2 is optimal)}}
+class LotsOfSpace {
+ Empty e1;
+ int i;
+ Empty e2;
+};
+
+// expected-warning@+1{{Excessive padding in 'TypedefSandwich2' (6 padding bytes, where 2 is optimal)}}
+typedef struct {
+ char c1;
+ // expected-warning@+1{{Excessive padding in 'TypedefSandwich2::NestedTypedef' (6 padding bytes, where 2 is optimal)}}
+ typedef struct {
+ char c1;
+ int i;
+ char c2;
+ } NestedTypedef;
+ NestedTypedef t;
+ char c2;
+} TypedefSandwich2;
+
+template <typename T>
+struct Foo {
+ // expected-warning@+1{{Excessive padding in 'struct Foo<int>::Nested' (6 padding bytes, where 2 is optimal)}}
+ struct Nested {
+ char c1;
+ T t;
+ char c2;
+ };
+};
+
+struct Holder { // no-warning
+ Foo<int>::Nested t1;
+ Foo<char>::Nested t2;
+};
Index: test/Analysis/padding_cpp.cpp
===================================================================
--- /dev/null
+++ test/Analysis/padding_cpp.cpp
@@ -0,0 +1,202 @@
+// RUN: %clang_cc1 -std=c++14 -analyze -analyzer-checker=performance -analyzer-config performance.Padding:AllowedPad=2 -verify %s
+
+// Make sure that the C cases still work fine, even when compiled as C++.
+#include "padding_c.c"
+
+struct BigCharArray2 { // no-warning
+ char c[129];
+};
+
+// xxxexpected-warning@+1{{Excessive padding in 'struct LowAlignmentBase'}}
+struct LowAlignmentBase : public BigCharArray2 {
+ int i;
+ char c;
+};
+
+struct CorrectLowAlignmentBase : public BigCharArray2 { // no-warning
+ char c;
+ int i;
+};
+
+// xxxexpected-warning@+1{{Excessive padding in 'struct LowAlignmentBase2'}}
+struct LowAlignmentBase2 : public BigCharArray2 {
+ char c1;
+ int i;
+ char c2;
+};
+
+class PaddedA { // expected-warning{{Excessive padding in 'class PaddedA'}}
+ char c1;
+ int i;
+ char c2;
+};
+
+class VirtualPaddedA : public PaddedA { // no-warning
+ virtual void foo() {}
+};
+
+class VirtualIntSandwich { // expected-warning{{Excessive padding in 'class VirtualIntSandwich'}}
+ virtual void foo() {}
+ char c1;
+ int i;
+ char c2;
+};
+
+// constructed so as not to have tail padding
+class InnerPaddedB { // expected-warning{{Excessive padding in 'class InnerPaddedB'}}
+ char c1;
+ int i1;
+ char c2;
+ int i2;
+};
+
+class TailPaddedB { // expected-warning{{Excessive padding in 'class TailPaddedB'}}
+ char c1;
+ int i1;
+ char c2;
+};
+
+class SI : public PaddedA { // no-warning
+ char c;
+};
+
+class SI2 : public PaddedA { // xxxexpected-warning{{Excessive padding in 'class SI2'}}
+ char c10;
+ int i10;
+ char c11;
+};
+
+class VirtualSI : virtual public PaddedA { // no-warning
+ char c;
+};
+
+// currently not checked for
+class VirtualSI2 : virtual public PaddedA { // no-warning
+ char c10;
+ int i10;
+ char c11;
+};
+
+class VtblSI : public PaddedA { // no-warning
+ virtual void foo() {}
+ char c;
+};
+
+class VtblSI2 : public PaddedA { // xxxexpected-warning{{Excessive padding in 'class VtblSI2'}}
+ virtual void foo() {}
+ char c10;
+ int i10;
+ char c11;
+};
+
+class VtblSI3 : public VirtualPaddedA { // xxxexpected-warning{{Excessive padding in 'class VtblSI3'}}
+ char c10;
+ int i10;
+ char c11;
+};
+
+class MI : public PaddedA, public InnerPaddedB { // no-warning
+ char c;
+};
+
+class MI2 : public PaddedA, public InnerPaddedB { // xxxexpected-warning{{Excessive padding in 'class MI2'}}
+ char c10;
+ int i10;
+ char c11;
+};
+
+class VtblMI : public PaddedA, public InnerPaddedB { // xxxexpected-warning{{Excessive padding in 'class VtblMI'}}
+ virtual void foo() {}
+ char c10;
+ int i10;
+ char c11;
+};
+
+class VtblMI2 : public VirtualPaddedA, public InnerPaddedB { // xxxexpected-warning{{Excessive padding in 'class VtblMI2'}}
+ char c10;
+ int i10;
+ char c11;
+};
+
+class Empty {}; // no-warning
+
+class LotsOfSpace { // expected-warning{{Excessive padding in 'class LotsOfSpace'}}
+ Empty e1;
+ int i;
+ Empty e2;
+};
+
+class EBO1 : public Empty { // xxxexpected-warning{{Excessive padding in 'class EBO1'}}
+ char c1;
+ int i;
+ char c2;
+};
+
+class EBO2 : public Empty { // xxxexpected-warning{{Excessive padding in 'class EBO2'}}
+ Empty c1;
+ int i;
+ Empty c2;
+};
+
+template <typename T>
+class TemplateSandwich { // expected-warning{{Excessive padding in 'class TemplateSandwich<int>' instantiated here}}
+ char c1;
+ T t;
+ char c2;
+};
+
+template <typename T>
+class TemplateSandwich<T *> { // expected-warning{{Excessive padding in 'class TemplateSandwich<void *>' instantiated here}}
+ char c1;
+ T *t;
+ char c2;
+};
+
+template <>
+class TemplateSandwich<long long> { // expected-warning{{Excessive padding in 'class TemplateSandwich<long long>' (}}
+ char c1;
+ long long t;
+ char c2;
+};
+
+class Holder1 { // no-warning
+ TemplateSandwich<int> t1;
+ TemplateSandwich<char> t2;
+ TemplateSandwich<void *> t3;
+};
+
+typedef struct { // expected-warning{{Excessive padding in 'TypedefSandwich2'}}
+ char c1;
+ typedef struct { // expected-warning{{Excessive padding in 'TypedefSandwich2::NestedTypedef'}}
+ char c1;
+ int i;
+ char c2;
+ } NestedTypedef;
+ NestedTypedef t;
+ char c2;
+} TypedefSandwich2;
+
+template <typename T>
+struct Foo {
+ // expected-warning@+1{{Excessive padding in 'struct Foo<int>::Nested'}}
+ struct Nested {
+ char c1;
+ T t;
+ char c2;
+ };
+};
+
+struct Holder { // no-warning
+ Foo<int>::Nested t1;
+ Foo<char>::Nested t2;
+};
+
+struct GlobalsForLambda { // no-warning
+ int i;
+ char c1;
+ char c2;
+} G;
+
+// expected-warning@+1{{Excessive padding in 'class (lambda}}
+auto lambda1 = [ c1 = G.c1, i = G.i, c2 = G.c2 ]{};
+auto lambda2 = [ i = G.i, c1 = G.c1, c2 = G.c2 ]{}; // no-warning
Index: test/Analysis/padding_c.c
===================================================================
--- /dev/null
+++ test/Analysis/padding_c.c
@@ -0,0 +1,243 @@
+// RUN: %clang_cc1 -analyze -analyzer-checker=performance -analyzer-config performance.Padding:AllowedPad=2 -verify %s
+
+#if __has_include(<stdalign.h>)
+#include <stdalign.h>
+#endif
+
+#if __has_include(<stdalign.h>) || defined(__cplusplus)
+// expected-warning@+1{{Excessive padding in 'struct FieldAttrAlign' (6 padding}}
+struct FieldAttrAlign {
+ char c1;
+ alignas(4) int i;
+ char c2;
+};
+
+// expected-warning@+1{{Excessive padding in 'struct FieldAttrOverAlign' (10 padding}}
+struct FieldAttrOverAlign {
+ char c1;
+ alignas(8) int i;
+ char c2;
+};
+
+#endif // __has_include(<stdalign.h>) || defined(__cplusplus)
+
+// Re-ordering members of these structs won't reduce padding, so don't warn
+struct LeadingChar { // no-warning
+ char c;
+ int i;
+};
+
+struct TrailingChar { // no-warning
+ int i;
+ char c;
+};
+
+struct Helpless { // no-warning
+ struct TrailingChar i1;
+ struct LeadingChar i2;
+ char c;
+};
+
+#pragma pack(push)
+#pragma pack(1)
+struct SquishedIntSandwich { // no-warning
+ char c1;
+ int i;
+ char c2;
+};
+#pragma pack(pop)
+
+// Re-ordering members of these structs will reduce padding, so warn
+struct IntSandwich { // expected-warning{{Excessive padding in 'struct IntSandwich'}}
+ char c1;
+ int i;
+ char c2;
+};
+
+struct TurDuckHen { // expected-warning{{Excessive padding in 'struct TurDuckHen'}}
+ char c1;
+ struct IntSandwich i;
+ char c2;
+};
+
+#pragma pack(push)
+#pragma pack(2)
+struct SmallIntSandwich { // expected-warning{{Excessive padding in 'struct SmallIntSandwich'}}
+ char c1;
+ int i1;
+ char c2;
+ int i2;
+ char c3;
+ int i3;
+ char c4;
+};
+#pragma pack(pop)
+
+union SomeUnion { // no-warning
+ char c;
+ short s;
+ int i;
+};
+
+struct HoldsAUnion { // expected-warning{{Excessive padding in 'struct HoldsAUnion'}}
+ char c1;
+ union SomeUnion u;
+ char c2;
+};
+
+struct BigCharArray { // no-warning
+ char c[129];
+};
+
+struct SmallCharArray { // no-warning
+ char c[5];
+};
+
+struct MediumIntArray { // no-warning
+ int i[5];
+};
+
+struct LargeSizeToSmallSize { // expected-warning{{Excessive padding in 'struct LargeSizeToSmallSize'}}
+ struct BigCharArray b;
+ struct MediumIntArray m;
+ struct SmallCharArray s;
+};
+
+struct LargeAlignToSmallAlign { // no-warning
+ struct MediumIntArray m;
+ struct BigCharArray b;
+ struct SmallCharArray s;
+};
+
+// Currently ignoring VLA padding problems. Still need to make sure we don't
+// choke on VLAs though
+struct HoldsVLA { // no-warning
+ char c1;
+ int x;
+ char c2;
+ int vla[];
+};
+
+// Currently ignoring bitfield padding problems. Still need to make sure we
+// don't choke on bitfields though
+struct HoldsBitfield { // no-warning
+ char c1;
+ int x;
+ char c2;
+ unsigned char b1 : 3;
+ unsigned char b2 : 3;
+ unsigned char b3 : 2;
+};
+
+typedef struct { // expected-warning{{Excessive padding in 'TypedefSandwich'}}
+ char c1;
+ int i;
+ char c2;
+} TypedefSandwich;
+
+// expected-warning@+1{{Excessive padding in 'struct StructAttrAlign' (10 padding}}
+struct StructAttrAlign {
+ char c1;
+ int i;
+ char c2;
+} __attribute__((aligned(8)));
+
+struct CorrectOverlyAlignedChar { // no-warning
+ char c __attribute__((aligned(4096)));
+ char c1;
+ int x1;
+ char c2;
+ int x2;
+ char c3;
+};
+
+struct OverlyAlignedChar { // expected-warning{{Excessive padding in 'struct OverlyAlignedChar'}}
+ char c1;
+ int x;
+ char c2;
+ char c __attribute__((aligned(4096)));
+};
+
+struct HoldsOverlyAlignedChar { // expected-warning{{Excessive padding in 'struct HoldsOverlyAlignedChar'}}
+ char c1;
+ struct OverlyAlignedChar o;
+ char c2;
+};
+
+void internalStructFunc() {
+ struct X { // expected-warning{{Excessive padding in 'struct X'}}
+ char c1;
+ int t;
+ char c2;
+ };
+ struct X obj;
+}
+
+void typedefStructFunc() {
+ typedef struct { // expected-warning{{Excessive padding in 'S'}}
+ char c1;
+ int t;
+ char c2;
+ } S;
+ S obj;
+}
+
+void anonStructFunc() {
+ struct { // expected-warning{{Excessive padding in 'struct (anonymous}}
+ char c1;
+ int t;
+ char c2;
+ } obj;
+}
+
+// expected-warning@+1{{Excessive padding in 'struct DefaultAttrAlign'}}
+struct DefaultAttrAlign {
+ char c1;
+ long long i;
+ char c2;
+} __attribute__((aligned));
+
+struct CorrectDefaultAttrAlign { // no-warning
+ long long i;
+ char c1;
+ char c2;
+} __attribute__((aligned));
+
+struct TooSmallShortSandwich { // no-warning
+ char c1;
+ short s;
+ char c2;
+};
+
+// expected-warning@+1{{Excessive padding in 'struct SmallArrayShortSandwich'}}
+struct SmallArrayShortSandwich {
+ char c1;
+ short s;
+ char c2;
+} ShortArray[20];
+
+// expected-warning@+1{{Excessive padding in 'struct SmallArrayInFunc'}}
+struct SmallArrayInFunc {
+ char c1;
+ short s;
+ char c2;
+};
+
+void arrayHolder() {
+ struct SmallArrayInFunc Arr[15];
+}
+
+// xxxexpected-warning@+1{{Excessive padding in 'struct SmallArrayInStruct'}}
+struct SmallArrayInStruct {
+ char c1;
+ short s;
+ char c2;
+};
+
+struct HoldsSmallArray {
+ struct SmallArrayInStruct Field[20];
+} HoldsSmallArrayElt;
+
+void nestedPadding() {
+ struct HoldsSmallArray Arr[15];
+}
Index: lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
===================================================================
--- /dev/null
+++ lib/StaticAnalyzer/Checkers/PaddingChecker.cpp
@@ -0,0 +1,314 @@
+//=======- PaddingChecker.cpp ------------------------------------*- C++ -*-==//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines a checker that checks for padding that could be
+// removed by re-ordering members.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/AST/CharUnits.h"
+#include "clang/AST/DeclTemplate.h"
+#include "clang/AST/RecordLayout.h"
+#include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/raw_ostream.h"
+#include <numeric>
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+class PaddingChecker : public Checker<check::ASTDecl<TranslationUnitDecl>> {
+private:
+ mutable std::unique_ptr<BugType> PaddingBug;
+ mutable int64_t AllowedPad;
+ mutable BugReporter *BR;
+
+public:
+ void checkASTDecl(const TranslationUnitDecl *TUD, AnalysisManager &MGR,
+ BugReporter &BRArg) const {
+ BR = &BRArg;
+ AllowedPad =
+ MGR.getAnalyzerOptions().getOptionAsInteger("AllowedPad", 24, this);
+ assert(AllowedPad >= 0 && "AllowedPad option should be non-negative");
+
+ // The calls to checkAST* from AnalysisConsumer don't
+ // visit template instantiations or lambda classes. We
+ // want to visit those, so we make our own RecursiveASTVisitor.
+ struct LocalVisitor : public RecursiveASTVisitor<LocalVisitor> {
+ const PaddingChecker *Checker;
+ bool shouldVisitTemplateInstantiations() const { return true; }
+ bool shouldVisitImplicitCode() const { return true; }
+ explicit LocalVisitor(const PaddingChecker *Checker) : Checker(Checker) {}
+ bool VisitRecordDecl(const RecordDecl *RD) {
+ Checker->visitRecord(RD);
+ return true;
+ }
+ bool VisitVarDecl(const VarDecl *VD) {
+ Checker->visitVariable(VD);
+ return true;
+ }
+ // TODO: Visit array new and mallocs for arrays.
+ };
+
+ LocalVisitor visitor(this);
+ visitor.TraverseDecl(const_cast<TranslationUnitDecl *>(TUD));
+ }
+
+ /// \brief Look for records of overly padded types. If padding *
+ /// PadMultiplier exceeds AllowedPad, then generate a report.
+ /// PadMultiplier is used to share code with the array padding
+ /// checker.
+ void visitRecord(const RecordDecl *RD, uint64_t PadMultiplier = 1) const {
+ if (shouldSkipDecl(RD))
+ return;
+
+ auto &ASTContext = RD->getASTContext();
+ const ASTRecordLayout &RL = ASTContext.getASTRecordLayout(RD);
+ assert(llvm::isPowerOf2_64(RL.getAlignment().getQuantity()));
+
+ CharUnits BaselinePad = calculateBaselinePad(RD, ASTContext, RL);
+ if (BaselinePad.isZero())
+ return;
+ CharUnits OptimalPad = calculateOptimalPad(RD, ASTContext, RL);
+
+ CharUnits DiffPad = PadMultiplier * (BaselinePad - OptimalPad);
+ if (DiffPad.getQuantity() <= AllowedPad) {
+ assert(!DiffPad.isNegative() && "DiffPad should not be negative");
+ // There is not enough excess padding to trigger a warning.
+ return;
+ }
+ reportRecord(RD, BaselinePad, OptimalPad);
+ }
+
+ /// \brief Look for arrays of overly padded types. If the padding of the
+ /// array type exceeds AllowedPad, then generate a report.
+ void visitVariable(const VarDecl *VD) const {
+ const ArrayType *ArrTy = VD->getType()->getAsArrayTypeUnsafe();
+ if (ArrTy == nullptr)
+ return;
+ uint64_t Elts = 0;
+ if (const ConstantArrayType *CArrTy = dyn_cast<ConstantArrayType>(ArrTy))
+ Elts = CArrTy->getSize().getZExtValue();
+ if (Elts == 0)
+ return;
+ const RecordType *RT = ArrTy->getElementType()->getAs<RecordType>();
+ if (RT == nullptr)
+ return;
+
+ // TODO: Recurse into the fields and base classes to see if any
+ // of those have excess padding.
+ visitRecord(RT->getDecl(), Elts);
+ }
+
+ bool shouldSkipDecl(const RecordDecl *RD) const {
+ auto Location = RD->getLocation();
+ // If the construct doesn't have a source file, then it's not something
+ // we want to diagnose.
+ if (!Location.isValid())
+ return true;
+ SrcMgr::CharacteristicKind Kind =
+ BR->getSourceManager().getFileCharacteristic(Location);
+ // Throw out all records that come from system headers.
+ if (Kind != SrcMgr::C_User)
+ return true;
+
+ // 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)
+ return true;
+ // Virtual bases are complicated, skipping those for now.
+ if (CXXRD->getNumVBases() != 0)
+ return true;
+ // Can't layout a template, so skip it. We do still layout the
+ // instantiations though.
+ if (CXXRD->getTypeForDecl()->isDependentType())
+ return true;
+ if (CXXRD->getTypeForDecl()->isInstantiationDependentType())
+ return true;
+ }
+ auto IsTrickyField = [](const FieldDecl *FD) -> bool {
+ // Bitfield layout is hard.
+ if (FD->isBitField())
+ return true;
+
+ // Variable length arrays are tricky too.
+ QualType Ty = FD->getType();
+ if (Ty->isIncompleteArrayType())
+ return true;
+ return false;
+ };
+
+ if (std::any_of(RD->field_begin(), RD->field_end(), IsTrickyField))
+ return true;
+ return false;
+ }
+
+ static CharUnits calculateBaselinePad(const RecordDecl *RD,
+ const ASTContext &ASTContext,
+ const ASTRecordLayout &RL) {
+ CharUnits PaddingSum;
+ CharUnits Offset = ASTContext.toCharUnitsFromBits(RL.getFieldOffset(0));
+ for (const auto &FD : RD->fields()) {
+ // This checker only cares about the padded size of the
+ // field, and not the data size. If the field is a record
+ // with tail padding, then we won't put that number in our
+ // total because reordering fields won't fix that problem.
+ CharUnits FieldSize = ASTContext.getTypeSizeInChars(FD->getType());
+ auto FieldOffsetBits = RL.getFieldOffset(FD->getFieldIndex());
+ CharUnits FieldOffset = ASTContext.toCharUnitsFromBits(FieldOffsetBits);
+ PaddingSum += (FieldOffset - Offset);
+ Offset = FieldOffset + FieldSize;
+ }
+ PaddingSum += RL.getSize() - Offset;
+ return PaddingSum;
+ }
+
+ /// Optimal padding overview:
+ /// 1. Find a close approximation to where we can place our first field.
+ /// This will usually be at offset 0.
+ /// 2. Try to find the best field that can legally be placed at the current
+ /// offset.
+ /// a. "Best" is the largest alignment that is legal, but smallest size.
+ /// This is to account for overly aligned types.
+ /// 3. If no fields can fit, pad by rounding the current offset up to our
+ /// lowest aligned field. Measure and track the amount of padding added.
+ /// Go back to 2.
+ /// 4. Increment the current offset by the size of the chosen field
+ /// 5. Remove the chosen field from the set of future possibilities
+ /// 6. Go back to 2 if there are still unplaced fields
+ /// 7. Add tail padding by rounding the current offset up to the structure
+ /// alignment. Track the amount of padding added.
+
+ static CharUnits calculateOptimalPad(const RecordDecl *RD,
+ const ASTContext &ASTContext,
+ const ASTRecordLayout &RL) {
+ struct CharUnitPair {
+ CharUnits Align;
+ CharUnits Size;
+ bool operator<(const CharUnitPair &RHS) const {
+ // Order from small alignments to large alignments,
+ // then large sizes to small sizes.
+ return std::make_pair(Align, -Size) <
+ std::make_pair(RHS.Align, -RHS.Size);
+ }
+ };
+ SmallVector<CharUnitPair, 20> Fields;
+ auto GatherSizesAndAlignments = [](const FieldDecl *FD) {
+ CharUnitPair RetVal;
+ auto &Ctx = FD->getASTContext();
+ std::tie(RetVal.Size, RetVal.Align) =
+ Ctx.getTypeInfoInChars(FD->getType());
+ assert(llvm::isPowerOf2_64(RetVal.Align.getQuantity()));
+ if (auto Max = FD->getMaxAlignment())
+ RetVal.Align = std::max(Ctx.toCharUnitsFromBits(Max), RetVal.Align);
+ return RetVal;
+ };
+ std::transform(RD->field_begin(), RD->field_end(),
+ std::back_inserter(Fields), GatherSizesAndAlignments);
+ std::sort(Fields.begin(), Fields.end());
+
+ // This lets us skip over vptrs and non-virtual bases,
+ // so that we can just worry about the fields in our object.
+ // Note that this does cause us to miss some cases where we
+ // could pack more bytes in to a base class's tail padding.
+ CharUnits NewOffset = ASTContext.toCharUnitsFromBits(RL.getFieldOffset(0));
+ CharUnits NewPad;
+
+ while (!Fields.empty()) {
+ unsigned TrailingZeros =
+ llvm::countTrailingZeros((unsigned long long)NewOffset.getQuantity());
+ // If NewOffset is zero, then countTrailingZeros will be 64. Shifting
+ // 64 will overflow our unsigned long long. Shifting 63 will turn
+ // our long long (and CharUnits internal type) negative. So shift 62.
+ long long CurAlignmentBits = 1ull << (std::min)(TrailingZeros, 62u);
+ CharUnits CurAlignment = CharUnits::fromQuantity(CurAlignmentBits);
+ CharUnitPair InsertPoint = {CurAlignment, CharUnits::Zero()};
+ auto CurBegin = Fields.begin();
+ auto CurEnd = Fields.end();
+
+ // In the typical case, this will find the last element
+ // of the vector. We won't find a middle element unless
+ // we started on a poorly aligned address or have an overly
+ // aligned field.
+ auto Iter = std::upper_bound(CurBegin, CurEnd, InsertPoint);
+ if (Iter != CurBegin) {
+ // We found a field that we can layout with the current alignment.
+ --Iter;
+ NewOffset += Iter->Size;
+ Fields.erase(Iter);
+ } else {
+ // We are poorly aligned, and we need to pad in order to layout another
+ // field. Round up to at least the smallest field aligment that we
+ // currently have.
+ CharUnits NextOffset = NewOffset.RoundUpToAlignment(Fields[0].Align);
+ NewPad += NextOffset - NewOffset;
+ NewOffset = NextOffset;
+ }
+ }
+ // Calculate tail padding.
+ CharUnits NewSize = NewOffset.RoundUpToAlignment(RL.getAlignment());
+ NewPad += NewSize - NewOffset;
+ return NewPad;
+ }
+
+ void reportRecord(const RecordDecl *RD, CharUnits BaselinePad,
+ CharUnits TargetPad) const {
+ if (!PaddingBug)
+ PaddingBug =
+ llvm::make_unique<BugType>(this, "Excessive Padding", "Performance");
+
+ SmallString<100> Buf;
+ llvm::raw_svector_ostream Os(Buf);
+
+ Os << "Excessive padding in '";
+ Os << QualType::getAsString(RD->getTypeForDecl(), Qualifiers()) << "'";
+
+ if (auto *TSD = dyn_cast<ClassTemplateSpecializationDecl>(RD)) {
+ // TODO: make this show up better in the console output and in
+ // the HTML. Maybe just make it show up in HTML like the path
+ // diagnostics show.
+ SourceLocation ILoc = TSD->getPointOfInstantiation();
+ if (ILoc.isValid())
+ Os << " instantiated here: "
+ << ILoc.printToString(BR->getSourceManager());
+ }
+
+ Os << " (" << BaselinePad.getQuantity() << " padding bytes, where "
+ << TargetPad.getQuantity() << " is optimal). Consider reordering "
+ << "the fields or adding explicit padding members.";
+
+ PathDiagnosticLocation CELoc =
+ PathDiagnosticLocation::create(RD, BR->getSourceManager());
+
+ auto Report = llvm::make_unique<BugReport>(*PaddingBug, Os.str(), CELoc);
+ Report->setDeclWithIssue(RD);
+ Report->addRange(RD->getSourceRange());
+
+ BR->emitReport(std::move(Report));
+ }
+};
+}
+
+void ento::registerPaddingChecker(CheckerManager &Mgr) {
+ Mgr.registerChecker<PaddingChecker>();
+}
Index: lib/StaticAnalyzer/Checkers/Checkers.td
===================================================================
--- lib/StaticAnalyzer/Checkers/Checkers.td
+++ lib/StaticAnalyzer/Checkers/Checkers.td
@@ -46,6 +46,8 @@
def DeadCode : Package<"deadcode">;
def DeadCodeAlpha : Package<"deadcode">, InPackage<Alpha>, Hidden;
+def Performance : Package<"performance">;
+
def Security : Package <"security">;
def InsecureAPI : Package<"insecureAPI">, InPackage<Security>;
def SecurityAlpha : Package<"security">, InPackage<Alpha>, Hidden;
@@ -273,6 +275,18 @@
} // end "alpha.deadcode"
//===----------------------------------------------------------------------===//
+// Performance checkers.
+//===----------------------------------------------------------------------===//
+
+let ParentPackage = Performance in {
+
+def PaddingChecker : Checker<"Padding">,
+ HelpText<"Check for excessively padded structs.">,
+ DescFile<"PaddingChecker.cpp">;
+
+} // end: "padding"
+
+//===----------------------------------------------------------------------===//
// Security checkers.
//===----------------------------------------------------------------------===//
Index: lib/StaticAnalyzer/Checkers/CMakeLists.txt
===================================================================
--- lib/StaticAnalyzer/Checkers/CMakeLists.txt
+++ lib/StaticAnalyzer/Checkers/CMakeLists.txt
@@ -57,6 +57,7 @@
ObjCMissingSuperCallChecker.cpp
ObjCSelfInitChecker.cpp
ObjCUnusedIVarsChecker.cpp
+ PaddingChecker.cpp
PointerArithChecker.cpp
PointerSubChecker.cpp
PthreadLockChecker.cpp
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