From bf3e3c162e2bd199effd17412813d8271dba40ee Mon Sep 17 00:00:00 2001
From: "Sven M. Hallberg" <pesco@khjk.org>
Date: Fri, 21 Jun 2013 15:31:37 +0200
Subject: [PATCH] don't even touch the right stack on piggy-back shifts
---
src/backends/lr.c | 26 ++++++++++++++------------
1 file changed, 14 insertions(+), 12 deletions(-)
diff --git a/src/backends/lr.c b/src/backends/lr.c
index 03264b5c..33d597b8 100644
--- a/src/backends/lr.c
+++ b/src/backends/lr.c
@@ -269,7 +269,6 @@ bool h_lrengine_step(HLREngine *engine, const HLRAction *action)
assert(action->type == HLR_SHIFT || action->type == HLR_REDUCE);
if(action->type == HLR_REDUCE) {
- assert(action->type == HLR_REDUCE);
size_t len = action->production.length;
HCFChoice *symbol = action->production.lhs;
@@ -306,21 +305,24 @@ bool h_lrengine_step(HLREngine *engine, const HLRAction *action)
if(symbol->action)
value = (HParsedToken *)symbol->action(make_result(arena, value));
- // push result (value, symbol) onto the right stack
- h_slist_push(right, value);
- h_slist_push(right, symbol);
-
// 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.
- action = h_lr_lookup(engine->table, engine->state, symbol);
- if(action == NULL)
- return false; // no handle after reduce; terminate
+ const HLRAction *next = h_lr_lookup(engine->table, engine->state, symbol);
+ if(next) {
+ assert(next->type == HLR_SHIFT);
+
+ // piggy-back the shift onto here, never touching the right stack
+ h_slist_push(left, (void *)(uintptr_t)engine->state);
+ h_slist_push(left, value);
+ engine->state = next->nextstate;
+ } else {
+ // fallback
+ h_slist_push(right, value);
+ h_slist_push(right, symbol);
+ }
+ } else {
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
--
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