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Cut down unnecessary zero'ing when value-initializing arrays of C++ objects. 

-C++ objects with user-declared constructor don't need zero'ing.
-We can zero-initialize arrays of C++ objects in "bulk" now, in which case don't zero-initialize each object again.

llvm-svn: 130453
This commit is contained in:
Argyrios Kyrtzidis 2011-04-28 22:57:55 +00:00
parent e69c748328
commit 03535265ef
3 changed files with 27 additions and 3 deletions
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11
clang/lib/CodeGen/CGExprAgg.cpp
View File

@ -811,7 +811,16 @@ static void CheckAggExprForMemSetUse(AggValueSlot &Slot, const Expr *E,
// If the slot is already known to be zeroed, nothing to do. Don't mess with
// volatile stores.
if (Slot.isZeroed() || Slot.isVolatile() || Slot.getAddr() == 0) return;
// C++ objects with a user-declared constructor don't need zero'ing.
if (CGF.getContext().getLangOptions().CPlusPlus)
if (const RecordType *RT = CGF.getContext()
.getBaseElementType(E->getType())->getAs<RecordType>()) {
const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
if (RD->hasUserDeclaredConstructor())
return;
}
// If the type is 16-bytes or smaller, prefer individual stores over memset.
std::pair<CharUnits, CharUnits> TypeInfo =
CGF.getContext().getTypeInfoInChars(E->getType());

5
clang/lib/CodeGen/CGExprCXX.cpp
View File

@ -370,8 +370,9 @@ CodeGenFunction::EmitCXXConstructExpr(const CXXConstructExpr *E,
// If we require zero initialization before (or instead of) calling the
// constructor, as can be the case with a non-user-provided default
// constructor, emit the zero initialization now.
if (E->requiresZeroInitialization())
// constructor, emit the zero initialization now, unless destination is
// already zeroed.
if (E->requiresZeroInitialization() && !Dest.isZeroed())
EmitNullInitialization(Dest.getAddr(), E->getType());
// If this is a call to a trivial default constructor, do nothing.

14
clang/test/CodeGenCXX/value-init.cpp
View File

@ -101,23 +101,37 @@ struct Test3 : public Test { };
// CHECK: define void @_ZN6PR98011fEv
void f() {
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98014TestC1Ei
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98014TestC1Ev
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98014TestC1Ev
Test partial[3] = { 1 };
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98014TestC1Ev
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98014TestC1Ev
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98014TestC1Ev
Test empty[3] = {};
// CHECK: call void @llvm.memset.p0i8.i64
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98015Test2C1Ev
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98015Test2C1Ev
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98015Test2C1Ev
Test2 empty2[3] = {};
// CHECK: call void @llvm.memset.p0i8.i64
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98015Test3C1Ev
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98015Test3C1Ev
// CHECK-NOT: call void @llvm.memset.p0i8.i64
// CHECK: call void @_ZN6PR98015Test3C1Ev
Test3 empty3[3] = {};
}