Function setAllocateOnStack

src/ast/ast_escape_analysis.cpp:226–257

set the stack-allocation flag on the fresh-alloc init expression; returns true if it changed it. only the shapes the codegen tiers can stack-allocate: a plain `new T()` (no initializer call, no dim) over a plain struct, and `new T(f=v)` which lowers to an ascend over a make-struct. capped by size. classes / constructors / handles are excluded: their construction has semantics (ctor invocation, rtt

    // capped by size. classes / constructors / handles are excluded: their construction has semantics
    // (ctor invocation, rtti) that the plain in-frame build does not reproduce (breaks under JIT).
    static bool setAllocateOnStack ( Expression * init ) {
        if ( init && init->rtti_isNewExpr() ) {
            auto en = (ExprNew *) init;
            auto st = en->typeexpr ? en->typeexpr->structType : nullptr;
            bool persistent = st && st->persistent;
            bool isClass = st && st->isClass;
            // use the non-asserting 64-bit size: a malformed/oversized type (e.g. in invalid_types.das)
            // yields a huge value that simply fails the cap, instead of tripping the size<=0x7fffffff assert
            bool fits = en->typeexpr && en->typeexpr->getBaseSizeOf64() <= uint64_t(MAX_STACK_ALLOC_SIZE);
            if ( !en->initializer && en->typeexpr && en->typeexpr->dim.empty() && !persistent && !isClass && fits && !en->allocate_on_stack ) {
                en->allocate_on_stack = true; return true;
            }
        } else if ( init && init->rtti_isAscend() ) {
            auto ea = (ExprAscend *) init;
            bool plainStruct = false;
            if ( ea->subexpr && ea->subexpr->rtti_isMakeStruct() ) {
                auto mks = (ExprMakeStruct *) ea->subexpr;
                auto st = mks->makeType ? mks->makeType->structType : nullptr;
                // note: isNewClass means "make-struct produced by a `new`" (set for plain structs too),
                // NOT "is a class" - the class signal is the constructor / forceClass / structType->isClass
                plainStruct = !mks->constructor && !mks->isNewHandle
                    && !mks->forceClass && !( st && st->isClass );
            }
            bool persistent = ea->subexpr && ea->subexpr->type && ea->subexpr->type->structType
                && ea->subexpr->type->structType->persistent;
            bool fits = ea->subexpr && ea->subexpr->type && ea->subexpr->type->getSizeOf64() <= uint64_t(MAX_STACK_ALLOC_SIZE);
            if ( plainStruct && !persistent && fits && !ea->allocate_on_stack ) {
                ea->allocate_on_stack = true; return true;
            }
        }
        return false;
    }

    static bool initIsAllocatedOnStack ( Expression * init ) {
        if ( init && init->rtti_isNewExpr() ) return ((ExprNew *)init)->allocate_on_stack;