Index: include/clang/AST/DeclCXX.h =================================================================== --- include/clang/AST/DeclCXX.h +++ include/clang/AST/DeclCXX.h @@ -357,6 +357,14 @@ /// \brief True when there are private non-static data members. bool HasPublicFields : 1; + /// \brief True is this class has already been checked as candidate + /// for writeonce semantics. + bool IsWriteOnceChecked : 1; + + /// \brief True if instances of this class are candidates + /// for writeonce semantics. + bool IsWriteOnceCandidate : 1; + /// \brief True if this class (or any subobject) has mutable fields. bool HasMutableFields : 1; @@ -766,6 +774,8 @@ return method_iterator(decls_end()); } + bool computeWriteOnceCandidacy() const; + /// Iterator access to constructor members. typedef specific_decl_iterator ctor_iterator; typedef llvm::iterator_range> Index: lib/AST/DeclCXX.cpp =================================================================== --- lib/AST/DeclCXX.cpp +++ lib/AST/DeclCXX.cpp @@ -58,6 +58,8 @@ HasPrivateFields(false), HasProtectedFields(false), HasPublicFields(false), + IsWriteOnceChecked(false), + IsWriteOnceCandidate(false), HasMutableFields(false), HasVariantMembers(false), HasOnlyCMembers(true), @@ -1348,6 +1350,73 @@ return false; } +/// \brief A class is a candidate for 'writeonce' semantics if +/// none of its methods writes to memory. +bool CXXRecordDecl::computeWriteOnceCandidacy() const { + // The class must be defined and concrete. + if (!isCompleteDefinition() || isDependentType()) return false; + + // If this has already been checked, then return the stored value. + if (data().IsWriteOnceChecked) return data().IsWriteOnceCandidate; + + // Otherwise, mark that this is checked. + data().IsWriteOnceChecked = true; + assert(!data().IsWriteOnceCandidate && + "The candidacy should not have been set yet."); + + // Check each method, excluding constructors and destructors. + // NOTE: The invariant intrinsic calls are generated right after the + // construction of a given const object (which must be initialized) + // and right before its destruction at the end of its lifetime. + // Both constructors and destructors modify the allocated memory and + // and will not be called in the middle of an invariant_start/end + // pair, thus may not affect the reduction of loads. So, it does not + // help to handle constructors here as well. + for (auto *M : methods()) { + if (isa(M) || isa(M)) continue; + + // If we already know that this method does not write to memory, skip it. + // NOTE: CodeGenModule::ConstructAttributeList() marks declarations with + // ConstAttr and PureAttr attributes, respectively, as 'readnone' and + // 'readonly' (for LLVM). + if (M->hasAttr() || M->hasAttr()) continue; + + const FunctionDecl *Def = nullptr; + bool IsDefined = M->isDefined(Def); + + // If this is not defined and not virtual, then it may write to memory. + // So it's not a candidate for 'writeonce' semantics. + // If it is purely virtual then it must be overriden and its overriding + // method (in this context) must be a candidate for 'writeonce' semantics. + // Skip it. + if (!IsDefined) { + if (M->isPure()) { + assert(M->isVirtual() && "Not defined and pure implies virtual."); + continue; + } + return false; + } + + // If this is trivial, skip it. + if (Def->hasTrivialBody()) continue; + + // TODO: Any other case? + } + + // Check bases + for (const auto &I : bases()) { + const RecordType *Ty = I.getType()->getAs(); + assert(Ty && "No type?"); + CXXRecordDecl *Base = + cast_or_null(Ty->getDecl()->getDefinition()); + + if (!Base || !Base->computeWriteOnceCandidacy()) return false; + } + + data().IsWriteOnceCandidate = true; + return true; +} + void CXXRecordDecl::completeDefinition() { completeDefinition(nullptr); } Index: lib/AST/Type.cpp =================================================================== --- lib/AST/Type.cpp +++ lib/AST/Type.cpp @@ -1937,8 +1937,15 @@ } bool QualType::isWriteOnce(ASTContext &Context) { - return (Context.getLangOpts().CPlusPlus && isConstant(Context) && - !getTypePtr()->isReferenceType()); + // TODO: Include C objects as well? + if (Context.getLangOpts().CPlusPlus && isConstant(Context) && + !getTypePtr()->isReferenceType()) { + if (const CXXRecordDecl *Record = + Context.getBaseElementType(*this)->getAsCXXRecordDecl()) + return Record->computeWriteOnceCandidacy(); + return true; + } + return false; } bool QualType::isPODType(ASTContext &Context) const { Index: test/CodeGenCXX/const-invariant.cpp =================================================================== --- test/CodeGenCXX/const-invariant.cpp +++ test/CodeGenCXX/const-invariant.cpp @@ -167,11 +167,11 @@ // CHECK-NL-CO-OBJ: call void @_ZN1MC{{[0-9]+}}Ei({{.*}}* @_ZL3i_m, {{.*}}) // CHECK-NL-CO-OBJ: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8* bitcast ({{.*}} @_ZL3i_m to i8*), // CHECK-NL-CO-OBJ: call void @_ZN1FC{{[0-9]+}}Ei({{.*}}* @_ZL3i_f, {{.*}}) -// CHECK-NL-CO-OBJ: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8* bitcast ({{.*}} @_ZL3i_f to i8*)) +// CHECK-NL-CO-OBJ-NOT: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8* bitcast ({{.*}} @_ZL3i_f to i8*)) // CHECK-NL-CO-OBJ: call void @_ZN1IC{{[0-9]+}}Ei({{.*}}* @_ZL3i_i, {{.*}}) // CHECK-NL-CO-OBJ: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8* bitcast ({{.*}} @_ZL3i_i to i8*)) // CHECK-NL-CO-OBJ: call void @_ZN2IVC{{[0-9]+}}Ei({{.*}}* @_ZL4i_iv, {{.*}}) -// CHECK-NL-CO-OBJ: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8* bitcast ({{.*}} @_ZL4i_iv to i8*)) +// CHECK-NL-CO-OBJ-NOT: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8* bitcast ({{.*}} @_ZL4i_iv to i8*)) // CHECK-NL-CO-OBJ: call void @_ZN3CIVC{{[0-9]+}}Ei({{.*}}* @_ZL5i_civ, {{.*}}) // CHECK-NL-CO-OBJ: call {{.*}}@llvm.invariant.start(i64 {{[0-9]+}}, i8* bitcast ({{.*}} @_ZL5i_civ to i8*)) @@ -303,11 +303,11 @@ // CHECK-L-CO-OBJ: %i_f = alloca {{.*}} // CHECK-L-CO-OBJ: call void @_ZN1FC{{[0-9]+}}Ei({{.*}}* %i_f, - // CHECK-L-CO-OBJ: call {{.*}}@llvm.invariant.start( + // CHECK-L-CO-OBJ-NOT: call {{.*}}@llvm.invariant.start( bar_f(i_f); foo_f(&i_f); // May change i_f. bar_f(i_f); - // CHECK-L-CO-OBJ: call {{.*}}@llvm.invariant.end( + // CHECK-L-CO-OBJ-NOT: call {{.*}}@llvm.invariant.end( } // Example 1 with type inheriting non-virtual base: @@ -337,11 +337,11 @@ // CHECK-L-CO-OBJ: %i_iv = alloca {{.*}} // CHECK-L-CO-OBJ: call void @_ZN2IVC{{[0-9]+}}Ei({{.*}}* %i_iv, - // CHECK-L-CO-OBJ: call {{.*}}@llvm.invariant.start( + // CHECK-L-CO-OBJ-NOT: call {{.*}}@llvm.invariant.start( bar_iv(i_iv); foo_iv(&i_iv); // Does not change i_iv. bar_iv(i_iv); - // CHECK-L-CO-OBJ: call {{.*}}@llvm.invariant.end( + // CHECK-L-CO-OBJ-NOT: call {{.*}}@llvm.invariant.end( } // Example 1 with type inheriting virtual writeonce base: