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piggy-back the next shift directly onto the reduce

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This commit is contained in:
Sven M. Hallberg 2013-06-21 15:06:31 +02:00
parent bbbaf1634c
commit 7cd143c0c4
1 changed files with 13 additions and 8 deletions
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21
src/backends/lr.c
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@ -268,12 +268,7 @@ bool h_lrengine_step(HLREngine *engine, const HLRAction *action)
assert(action->type == HLR_SHIFT || action->type == HLR_REDUCE);
if(action->type == HLR_SHIFT) {
h_slist_push(left, (void *)(uintptr_t)engine->state);
h_slist_drop(right); // symbol (discard)
h_slist_push(left, h_slist_drop(right)); // semantic value
engine->state = action->nextstate;
} else {
if(action->type == HLR_REDUCE) {
assert(action->type == HLR_REDUCE);
size_t len = action->production.length;
HCFChoice *symbol = action->production.lhs;
@ -318,8 +313,18 @@ bool h_lrengine_step(HLREngine *engine, const HLRAction *action)
// this is LR, building a right-most derivation bottom-up, so no reduce can
// follow a reduce. we can also assume no conflict follows for GLR if we
// use LALR tables, because only terminal symbols (lookahead) get reduces.
const HLRAction *next = h_lr_lookup(engine->table, engine->state, symbol);
assert(next == NULL || next->type == HLR_SHIFT);
action = h_lr_lookup(engine->table, engine->state, symbol);
if(action == NULL)
return false; // no handle after reduce; terminate
assert(action->type == HLR_SHIFT);
}
// this could be the original action, or a shift piggy-backed onto reduce
if(action->type == HLR_SHIFT) {
h_slist_push(left, (void *)(uintptr_t)engine->state);
h_slist_drop(right); // symbol (discard)
h_slist_push(left, h_slist_drop(right)); // semantic value
engine->state = action->nextstate;
}
return true;