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[CodeGen][typeid] Emit typeinfo directly if type is known at compile-time

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Differential Revision: https://reviews.llvm.org/D87425
This commit is contained in:
Zequan Wu 2020-09-14 10:57:23 -07:00
parent 69f98311ca
commit f975ae4867
4 changed files with 23 additions and 4 deletions
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4
clang/include/clang/AST/ExprCXX.h
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@ -858,6 +858,10 @@ public:
/// evaluated, per C++11 [expr.typeid]p3.
bool isPotentiallyEvaluated() const;
/// Best-effort check if the expression operand refers to a most derived
/// object. This is not a strong guarantee.
bool isMostDerived(ASTContext &Context) const;
bool isTypeOperand() const { return Operand.is<TypeSourceInfo *>(); }
/// Retrieves the type operand of this typeid() expression after

12
clang/lib/AST/ExprCXX.cpp
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@ -146,6 +146,18 @@ bool CXXTypeidExpr::isPotentiallyEvaluated() const {
return false;
}
bool CXXTypeidExpr::isMostDerived(ASTContext &Context) const {
assert(!isTypeOperand() && "Cannot call isMostDerived for typeid(type)");
const Expr *E = getExprOperand()->IgnoreParenNoopCasts(Context);
if (const auto *DRE = dyn_cast<DeclRefExpr>(E)) {
QualType Ty = DRE->getDecl()->getType();
if (!Ty->isPointerType() && !Ty->isReferenceType())
return true;
}
return false;
}
QualType CXXTypeidExpr::getTypeOperand(ASTContext &Context) const {
assert(isTypeOperand() && "Cannot call getTypeOperand for typeid(expr)");
Qualifiers Quals;

3
clang/lib/CodeGen/CGExprCXX.cpp
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@ -2199,7 +2199,8 @@ llvm::Value *CodeGenFunction::EmitCXXTypeidExpr(const CXXTypeidExpr *E) {
// polymorphic class type, the result refers to a std::type_info object
// representing the type of the most derived object (that is, the dynamic
// type) to which the glvalue refers.
if (E->isPotentiallyEvaluated())
// If the operand is already most derived object, no need to look up vtable.
if (E->isPotentiallyEvaluated() && !E->isMostDerived(getContext()))
return EmitTypeidFromVTable(*this, E->getExprOperand(),
StdTypeInfoPtrTy);

8
clang/test/CodeGenCXX/microsoft-abi-typeid.cpp
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@ -46,9 +46,11 @@ const std::type_info* test4_typeid() { return &typeid(b); }
const std::type_info* test5_typeid() { return &typeid(v); }
// CHECK: define dso_local %struct.type_info* @"?test5_typeid@@YAPBUtype_info@@XZ"()
// CHECK: [[RT:%.*]] = call i8* @__RTtypeid(i8* bitcast (%struct.V* @"?v@@3UV@@A" to i8*))
// CHECK-NEXT: [[RET:%.*]] = bitcast i8* [[RT]] to %struct.type_info*
// CHECK-NEXT: ret %struct.type_info* [[RET]]
// CHECK: ret %struct.type_info* bitcast (%rtti.TypeDescriptor7* @"??_R0?AUV@@@8" to %struct.type_info*)
const std::type_info *test6_typeid() { return &typeid((V &)v); }
// CHECK: define dso_local %struct.type_info* @"?test6_typeid@@YAPBUtype_info@@XZ"()
// CHECK: ret %struct.type_info* bitcast (%rtti.TypeDescriptor7* @"??_R0?AUV@@@8" to %struct.type_info*)
namespace PR26329 {
struct Polymorphic {