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Unroll first iteration of ExprSelect loop to avoid thunk allocation
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infinisil committed Oct 21, 2020
1 parent e8fbaf6 commit 48511ea
Showing 1 changed file with 58 additions and 7 deletions.
65 changes: 58 additions & 7 deletions src/libexpr/eval.cc
Expand Up @@ -1172,14 +1172,40 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
// TODO: Probably use pos2 throughout this function
Pos * pos2 = 0;

// TODO: [Why] can't this be stack allocated. Same for evalAttr
Value * vAttrs = e->maybeThunk(state, env);
Value vTmp;
Value * vAttrs = &vTmp;

try {

for (auto & i : attrPath) {
auto i = attrPath.begin();

// In the first loop iteration, we evaluate an attribute of an Expr, and not a Value
// So by unrolling this, we can avoid a thunk allocation by using e->evalAttr instead of evalValueAttr
nrLookups++;
Symbol name = getName(*i, state, env);
Attr * attr = e->evalAttr(state, env, *vAttrs, name);
if (!attr) {
if (def) {
def->eval(state, env, v);
return;
} else {
// Depending on the reason of j being null we throw an error
// If it wasn't an attribute set, this should trigger
state.forceAttrs(*vAttrs, pos);
// Otherwise the attribute set will have missed the name we wanted
throwEvalError(pos, "attribute '%1%' missing", name);
}
}
vAttrs = attr->value;
pos2 = attr->pos;
if (state.countCalls && pos2) state.attrSelects[*pos2]++;

++i;


for (;i < attrPath.end(); ++i) {
nrLookups++;
Symbol name = getName(i, state, env);
Symbol name = getName(*i, state, env);
Attr * attr = state.evalValueAttr(*vAttrs, name, pos);
if (!attr) {
if (def) {
Expand Down Expand Up @@ -1213,13 +1239,38 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
Attr * ExprSelect::evalAttr(EvalState & state, Env & env, Value & v, const Symbol & name)
{
Pos * pos2 = 0;
Value * vAttrs = e->maybeThunk(state, env);
Value vTmp;
Value * vAttrs = &vTmp;

try {

for (auto & i : attrPath) {
auto i = attrPath.begin();

// In the first loop iteration, we evaluate an attribute of an Expr, and not a Value
// So by unrolling this, we can avoid a thunk allocation by using e->evalAttr instead of evalValueAttr
nrLookups++;
Symbol name2 = getName(*i, state, env);
Attr * attr = e->evalAttr(state, env, *vAttrs, name2);
if (!attr) {
if (def) {
return def->evalAttr(state, env, v, name);
} else {
// Depending on the reason of j being null we throw an error
// If it wasn't an attribute set, this should trigger
state.forceAttrs(*vAttrs, pos);
// Otherwise the attribute set will have missed the name we wanted
throwEvalError(pos, "attribute '%1%' missing", name);
}
}
vAttrs = attr->value;
pos2 = attr->pos;
if (state.countCalls && pos2) state.attrSelects[*pos2]++;

++i;

for (;i < attrPath.end(); ++i) {
nrLookups++;
Symbol name2 = getName(i, state, env);
Symbol name2 = getName(*i, state, env);
Attr * attr = state.evalValueAttr(*vAttrs, name2, pos);
if (!attr) {
if (def) {
Expand Down

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