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Optimization/simplification of 'getbaseline'

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By producing absolute line information at regular intervals, a simple
division can compute the correct entry for a given instruction.
This commit is contained in:
Roberto Ierusalimschy
2021-02-02 14:43:55 -03:00
parent 949187b049
commit e500892e18
3 changed files with 19 additions and 24 deletions
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35
ldebug.c
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@@ -46,10 +46,14 @@ static int currentpc (CallInfo *ci) {
/*
** Get a "base line" to find the line corresponding to an instruction.
** For that, search the array of absolute line info for the largest saved
** instruction smaller or equal to the wanted instruction. A special
** case is when there is no absolute info or the instruction is before
** the first absolute one.
** Base lines are regularly placed at MAXIWTHABS intervals, so usually
** an integer division gets the right place. When the source file has
** large sequences of empty/comment lines, it may need extra entries,
** so the original estimate needs a correction.
** The assertion that the estimate is a lower bound for the correct base
** is valid as long as the debug info has been generated with the same
** value for MAXIWTHABS or smaller. (Previous releases use a little
** smaller value.)
*/
static int getbaseline (const Proto *f, int pc, int *basepc) {
if (f->sizeabslineinfo == 0 || pc < f->abslineinfo[0].pc) {
@@ -57,20 +61,11 @@ static int getbaseline (const Proto *f, int pc, int *basepc) {
return f->linedefined;
}
else {
unsigned int i;
if (pc >= f->abslineinfo[f->sizeabslineinfo - 1].pc)
i = f->sizeabslineinfo - 1; /* instruction is after last saved one */
else { /* binary search */
unsigned int j = f->sizeabslineinfo - 1; /* pc < anchorlines[j] */
i = 0; /* abslineinfo[i] <= pc */
while (i < j - 1) {
unsigned int m = (j + i) / 2;
if (pc >= f->abslineinfo[m].pc)
i = m;
else
j = m;
}
}
int i = cast_uint(pc) / MAXIWTHABS - 1; /* get an estimate */
/* estimate must be a lower bond of the correct base */
lua_assert(i < f->sizeabslineinfo && f->abslineinfo[i].pc <= pc);
while (i + 1 < f->sizeabslineinfo && pc >= f->abslineinfo[i + 1].pc)
i++; /* low estimate; adjust it */
*basepc = f->abslineinfo[i].pc;
return f->abslineinfo[i].line;
}
@@ -303,8 +298,8 @@ static void collectvalidlines (lua_State *L, Closure *f) {
sethvalue2s(L, L->top, t); /* push it on stack */
api_incr_top(L);
setbtvalue(&v); /* boolean 'true' to be the value of all indices */
for (i = 0; i < p->sizelineinfo; i++) { /* for all lines with code */
currentline = nextline(p, currentline, i);
for (i = 0; i < p->sizelineinfo; i++) { /* for all instructions */
currentline = nextline(p, currentline, i); /* get its line */
luaH_setint(L, t, currentline, &v); /* table[line] = true */
}
}