Perform two more constructor/destructor code-size optimizations:
1) emit base destructors as aliases to their unique base class destructors
under some careful conditions. This is enabled for the same targets that can
support complete-to-base aliases, i.e. not darwin.
2) Emit non-variadic complete constructors for classes with no virtual bases
as calls to the base constructor. This is enabled on all targets and in
theory can trigger in situations that the alias optimization can't (mostly
involving virtual bases, mostly not yet supported).
These are bundled together because I didn't think it worthwhile to split them,
not because they really need to be.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@96842 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGClass.cpp b/lib/CodeGen/CGClass.cpp
index d30d218..99c6dfd 100644
--- a/lib/CodeGen/CGClass.cpp
+++ b/lib/CodeGen/CGClass.cpp
@@ -891,31 +891,80 @@
}
}
+/// Checks whether the given constructor is a valid subject for the
+/// complete-to-base constructor delegation optimization, i.e.
+/// emitting the complete constructor as a simple call to the base
+/// constructor.
+static bool IsConstructorDelegationValid(const CXXConstructorDecl *Ctor) {
+
+ // Currently we disable the optimization for classes with virtual
+ // bases because (1) the addresses of parameter variables need to be
+ // consistent across all initializers but (2) the delegate function
+ // call necessarily creates a second copy of the parameter variable.
+ //
+ // The limiting example (purely theoretical AFAIK):
+ // struct A { A(int &c) { c++; } };
+ // struct B : virtual A {
+ // B(int count) : A(count) { printf("%d\n", count); }
+ // };
+ // ...although even this example could in principle be emitted as a
+ // delegation since the address of the parameter doesn't escape.
+ if (Ctor->getParent()->getNumVBases()) {
+ // TODO: white-list trivial vbase initializers. This case wouldn't
+ // be subject to the restrictions below.
+
+ // TODO: white-list cases where:
+ // - there are no non-reference parameters to the constructor
+ // - the initializers don't access any non-reference parameters
+ // - the initializers don't take the address of non-reference
+ // parameters
+ // - etc.
+ // If we ever add any of the above cases, remember that:
+ // - function-try-blocks will always blacklist this optimization
+ // - we need to perform the constructor prologue and cleanup in
+ // EmitConstructorBody.
+
+ return false;
+ }
+
+ // We also disable the optimization for variadic functions because
+ // it's impossible to "re-pass" varargs.
+ if (Ctor->getType()->getAs<FunctionProtoType>()->isVariadic())
+ return false;
+
+ return true;
+}
+
/// EmitConstructorBody - Emits the body of the current constructor.
void CodeGenFunction::EmitConstructorBody(FunctionArgList &Args) {
const CXXConstructorDecl *Ctor = cast<CXXConstructorDecl>(CurGD.getDecl());
CXXCtorType CtorType = CurGD.getCtorType();
+ // Before we go any further, try the complete->base constructor
+ // delegation optimization.
+ if (CtorType == Ctor_Complete && IsConstructorDelegationValid(Ctor)) {
+ EmitDelegateCXXConstructorCall(Ctor, Ctor_Base, Args);
+ return;
+ }
+
Stmt *Body = Ctor->getBody();
- // Some of the optimizations we want to do can't be done with
- // function try blocks.
+ // Enter the function-try-block before the constructor prologue if
+ // applicable.
CXXTryStmtInfo TryInfo;
- bool isTryBody = (Body && isa<CXXTryStmt>(Body));
- if (isTryBody)
+ bool IsTryBody = (Body && isa<CXXTryStmt>(Body));
+
+ if (IsTryBody)
TryInfo = EnterCXXTryStmt(*cast<CXXTryStmt>(Body));
unsigned CleanupStackSize = CleanupEntries.size();
- // Emit the constructor prologue, i.e. the base and member initializers.
-
- // TODO: for non-variadic complete-object constructors without a
- // function try block for a body, we can get away with just emitting
- // the vbase initializers, then calling the base constructor.
+ // Emit the constructor prologue, i.e. the base and member
+ // initializers.
EmitCtorPrologue(Ctor, CtorType);
// Emit the body of the statement.
- if (isTryBody)
+ if (IsTryBody)
EmitStmt(cast<CXXTryStmt>(Body)->getTryBlock());
else if (Body)
EmitStmt(Body);
@@ -933,7 +982,7 @@
// constructed.
EmitCleanupBlocks(CleanupStackSize);
- if (isTryBody)
+ if (IsTryBody)
ExitCXXTryStmt(*cast<CXXTryStmt>(Body), TryInfo);
}
@@ -1406,6 +1455,71 @@
EmitCXXMemberCall(D, Callee, ReturnValueSlot(), This, VTT, ArgBeg, ArgEnd);
}
+void
+CodeGenFunction::EmitDelegateCXXConstructorCall(const CXXConstructorDecl *Ctor,
+ CXXCtorType CtorType,
+ const FunctionArgList &Args) {
+ CallArgList DelegateArgs;
+
+ FunctionArgList::const_iterator I = Args.begin(), E = Args.end();
+ assert(I != E && "no parameters to constructor");
+
+ // this
+ DelegateArgs.push_back(std::make_pair(RValue::get(LoadCXXThis()),
+ I->second));
+ ++I;
+
+ // vtt
+ if (llvm::Value *VTT = GetVTTParameter(*this, GlobalDecl(Ctor, CtorType))) {
+ QualType VoidPP = getContext().getPointerType(getContext().VoidPtrTy);
+ DelegateArgs.push_back(std::make_pair(RValue::get(VTT), VoidPP));
+
+ if (CGVtableInfo::needsVTTParameter(CurGD)) {
+ assert(I != E && "cannot skip vtt parameter, already done with args");
+ assert(I->second == VoidPP && "skipping parameter not of vtt type");
+ ++I;
+ }
+ }
+
+ // Explicit arguments.
+ for (; I != E; ++I) {
+
+ const VarDecl *Param = I->first;
+ QualType ArgType = Param->getType(); // because we're passing it to itself
+
+ // StartFunction converted the ABI-lowered parameter(s) into a
+ // local alloca. We need to turn that into an r-value suitable
+ // for EmitCall.
+ llvm::Value *Local = GetAddrOfLocalVar(Param);
+ RValue Arg;
+
+ // For the most part, we just need to load the alloca, except:
+ // 1) aggregate r-values are actually pointers to temporaries, and
+ // 2) references to aggregates are pointers directly to the aggregate.
+ // I don't know why references to non-aggregates are different here.
+ if (ArgType->isReferenceType()) {
+ const ReferenceType *RefType = ArgType->getAs<ReferenceType>();
+ if (hasAggregateLLVMType(RefType->getPointeeType()))
+ Arg = RValue::getAggregate(Local);
+ else
+ // Locals which are references to scalars are represented
+ // with allocas holding the pointer.
+ Arg = RValue::get(Builder.CreateLoad(Local));
+ } else {
+ if (hasAggregateLLVMType(ArgType))
+ Arg = RValue::getAggregate(Local);
+ else
+ Arg = RValue::get(EmitLoadOfScalar(Local, false, ArgType));
+ }
+
+ DelegateArgs.push_back(std::make_pair(Arg, ArgType));
+ }
+
+ EmitCall(CGM.getTypes().getFunctionInfo(Ctor, CtorType),
+ CGM.GetAddrOfCXXConstructor(Ctor, CtorType),
+ ReturnValueSlot(), DelegateArgs, Ctor);
+}
+
void CodeGenFunction::EmitCXXDestructorCall(const CXXDestructorDecl *DD,
CXXDtorType Type,
llvm::Value *This) {