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tables: avoid warnings and save bits

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The yydefgoto table uses -1 as an invalid for an impossible case (we
never use yydefgoto[0], since it corresponds to the reduction to
$accept, which never happens).  Since yydefgoto is a table of state
numbers, this -1 forces a signed type uselessly, which (1) might
trigger compiler warnings when storing a value from yydefgoto into a
state number (nonnegative), and (2) wastes bits which might result in
using a int16 where a uint8 suffices.

Reported by Jot Dot <jotdot@shaw.ca>.
https://lists.gnu.org/r/bug-bison/2020-11/msg00027.html

* src/tables.c (default_goto): Use 0 rather than -1 as invalid value.
* tests/regression.at: Adjust.
This commit is contained in:
Akim Demaille
2020-12-02 21:39:26 +01:00
parent 89d2b69c1b
commit 1d3df34671
4 changed files with 29 additions and 10 deletions
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9
src/tables.c
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@@ -512,7 +512,14 @@ default_goto (symbol_number sym, size_t state_count[])
{
const goto_number begin = goto_map[sym - ntokens];
const goto_number end = goto_map[sym - ntokens + 1];
state_number res = -1;
/* In the case this symbol is never reduced to ($accept), use state
0. We used to use -1, but as a result the yydefgoto table must
be signed, which (1) might trigger compiler warnings when storing
a value from yydefgoto into a state number (nonnegative), and (2)
wastes bits which might result in using a int16 where a uint8
suffices. */
state_number res = 0;
if (begin != end)
{