Profiled 4glc compiling a 7737 line module (callgrind, since perf is not
permitted here). Two things dominated, and neither was what I expected.
1. A4GL_get_current_comments() declared
char buff[200000]="";
An initialiser on an array that size makes the compiler zero all 200KB on
entry, and the function is called once per command - 53512 times in that
module, about 10GB of memset, 41% of total run time. Everything below
treats buff as a C string (strlen/strcat/strdup), so terminating the first
byte is all that is needed. The redundant strcpy(buff,"") that immediately
followed it goes too.
2. FGLPARSE_allow_token_state() was the linear scan version. The token groups
average about 120 entries, and the lexer calls this for every word that
spells a reserved word, so it was 23% of what remained. states_optimised.c
already generates the same table sorted with a bsearch lookup - it just was
not linked, because WANTKW_C pointed at mk_states.c. It now points at
states_optimised.c, using the absolute path the existing build rule for
that file defines.
7737 lines: 0.58s -> 0.39s
instructions: 21.6G -> 12.9G after (1); (2) took the remainder down
further
Both verified. The comment change was A/B'd on the path that actually uses
comments - A4GL_LEXTYPE=WRITE, which stores them in the .dat for fgllint -
and the output is byte identical apart from the embedded compile timestamp
(one byte, at offset 361, 28 seconds apart between the two runs). The full
aubit4gltest run (-esqli -tui, all 21 ranges) is unchanged at 1098 run, 33
failed, 1065 passed.
What is left is the semantic value stack. The %union carries char str[12288],
so sizeof(YYSTYPE) is 12KB, and bison copies that on every shift
("*++yyvsp = yylval") and every reduction ("yyval = yyvsp[1-yylen]"). That is
now 54% of the remaining time, and YYINITDEPTH 200 also puts a 2.4MB array on
the stack. Making str a pointer would remove most of it, but it touches every
$$.str in the .rule files, so it is not a change to make casually.
