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Speed up SSA liveness analysis #264

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Merged
jserv merged 1 commit into from
Aug 26, 2025
Merged

Speed up SSA liveness analysis #264

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71 changes: 63 additions & 8 deletions src/ssa.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2003,16 +2003,50 @@ void compute_live_in(basic_block_t *bb)

int merge_live_in(var_t *live_out[], int live_out_idx, basic_block_t *bb)
{
for (int i = 0; i < bb->live_in_idx; i++) {
int found = 0;
for (int j = 0; j < live_out_idx; j++) {
if (live_out[j] == bb->live_in[i]) {
found = 1;
break;
/* Early exit for empty live_in */
if (bb->live_in_idx == 0)
return live_out_idx;

/* Optimize for common case of small sets */
if (live_out_idx < 16) {
/* For small sets, simple linear search is fast enough */
for (int i = 0; i < bb->live_in_idx; i++) {
int found = 0;
for (int j = 0; j < live_out_idx; j++) {
if (live_out[j] == bb->live_in[i]) {
found = 1;
break;
}
}
if (!found && live_out_idx < MAX_ANALYSIS_STACK_SIZE)
live_out[live_out_idx++] = bb->live_in[i];
}
} else {
/* For larger sets, check bounds and use optimized loop */
for (int i = 0; i < bb->live_in_idx; i++) {
int found = 0;
var_t *var = bb->live_in[i];
/* Unroll inner loop for better performance */
int j;
for (j = 0; j + 3 < live_out_idx; j += 4) {
if (live_out[j] == var || live_out[j + 1] == var ||
live_out[j + 2] == var || live_out[j + 3] == var) {
found = 1;
break;
}
}
/* Handle remaining elements */
if (!found) {
for (; j < live_out_idx; j++) {
if (live_out[j] == var) {
found = 1;
break;
}
}
}
if (!found && live_out_idx < MAX_ANALYSIS_STACK_SIZE)
live_out[live_out_idx++] = var;
}
if (!found)
live_out[live_out_idx++] = bb->live_in[i];
}
return live_out_idx;
}
Expand All @@ -2022,6 +2056,7 @@ bool recompute_live_out(basic_block_t *bb)
var_t *live_out[MAX_ANALYSIS_STACK_SIZE];
int live_out_idx = 0;

/* Compute union of successor live_in sets */
if (bb->next) {
compute_live_in(bb->next);
live_out_idx = merge_live_in(live_out, live_out_idx, bb->next);
Expand All @@ -2035,12 +2070,32 @@ bool recompute_live_out(basic_block_t *bb)
live_out_idx = merge_live_in(live_out, live_out_idx, bb->else_);
}

/* Quick check: if sizes differ, sets must be different */
if (bb->live_out_idx != live_out_idx) {
memcpy(bb->live_out, live_out, HOST_PTR_SIZE * live_out_idx);
bb->live_out_idx = live_out_idx;
return true;
}

/* Size is same, need to check if contents are identical */
/* Optimize by checking if first few elements match (common case) */
if (live_out_idx > 0) {
/* Quick check first element */
bool first_found = false;
for (int j = 0; j < bb->live_out_idx; j++) {
if (live_out[0] == bb->live_out[j]) {
first_found = true;
break;
}
}
if (!first_found) {
memcpy(bb->live_out, live_out, HOST_PTR_SIZE * live_out_idx);
bb->live_out_idx = live_out_idx;
return true;
}
}

/* Full comparison */
for (int i = 0; i < live_out_idx; i++) {
int same = 0;
for (int j = 0; j < bb->live_out_idx; j++) {
Expand Down