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Named Return Value Optimization

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This commit is contained in:
Alexey Prokhin
2011-09-13 12:01:51 +04:00
parent 0e754b5acd
commit 9a9999854f
6 changed files with 55 additions and 23 deletions
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43
gen/llvmhelpers.cpp
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@@ -1007,10 +1007,48 @@ DValue* DtoDeclarationExp(Dsymbol* declaration)
Logger::println("has nestedref set");
assert(vd->ir.irLocal);
DtoNestedInit(vd);
// is it already allocated?
} else if(vd->ir.irLocal) {
// nothing to do...
}
// normal stack variable, allocate storage on the stack if it has not already been done
else if(!vd->ir.irLocal && !vd->isRef()) {
#if DMDV2
/* Named Return Value Optimization (NRVO):
T f(){
T ret; // &ret == hidden pointer
ret = ...
return ret; // NRVO.
}
*/
else if (gIR->func()->retArg && gIR->func()->decl->nrvo_can && gIR->func()->decl->nrvo_var == vd) {
vd->ir.irLocal = new IrLocal(vd);
vd->ir.irLocal->value = gIR->func()->retArg;
}
#endif
// normal stack variable, allocate storage on the stack if it has not already been done
else if(!vd->isRef()) {
vd->ir.irLocal = new IrLocal(vd);
#if DMDV2
/* NRVO again:
T t = f(); // t's memory address is taken hidden pointer
*/
ExpInitializer *ei = 0;
if (vd->type->toBasetype()->ty == Tstruct && vd->init &&
!!(ei = vd->init->isExpInitializer()))
{
if (ei->exp->op == TOKconstruct) {
AssignExp *ae = (AssignExp*)ei->exp;
if (ae->e2->op == TOKcall) {
CallExp *ce = (CallExp *)ae->e2;
TypeFunction *tf = (TypeFunction *)ce->e1->type->toBasetype();
if (tf->ty == Tfunction && tf->retStyle() == RETstack) {
vd->ir.irLocal->value = ce->toElem(gIR)->getLVal();
goto Lexit;
}
}
}
}
#endif
const LLType* lltype = DtoType(vd->type);
@@ -1039,6 +1077,7 @@ DValue* DtoDeclarationExp(Dsymbol* declaration)
DtoInitializer(vd->ir.irLocal->value, vd->init); // TODO: Remove altogether?
#if DMDV2
Lexit:
/* Mark the point of construction of a variable that needs to be destructed.
*/
if (vd->edtor && !vd->noscope)