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read_locals: save some memory for redundant locals #32

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read_locals: save some memory for redundant locals #32

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37 changes: 37 additions & 0 deletions lib/module.c
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Original file line number Diff line number Diff line change
Expand Up @@ -819,6 +819,7 @@ read_locals(const uint8_t **pp, const uint8_t *ep, struct func *func,

uint32_t i;
struct localchunk *chunk = chunks;
struct localchunk *prev = NULL;
for (i = 0; i < vec_count; i++) {
uint32_t count;
uint8_t u8;
Expand Down Expand Up @@ -847,10 +848,46 @@ read_locals(const uint8_t **pp, const uint8_t *ep, struct func *func,
*/
continue;
}
/*
* some tools (wasm-opt?) sometimes generate
* locals like:
*
* 00aac9 func[31]:
* 00aaca: 01 7f | local[16] type=i32
* 00aacc: 01 7f | local[17] type=i32
* 00aace: 01 7f | local[18] type=i32
* 00aad0: 01 7f | local[19] type=i32
* 00aad2: 01 7f | local[20] type=i32
* 00aad4: 01 7f | local[21] type=i32
* 00aad6: 01 7f | local[22] type=i32
* 00aad8: 01 7f | local[23] type=i32
* 00aada: 01 7f | local[24] type=i32
* 00aadc: 01 7f | local[25] type=i32
*
* the following logic is intended to pack it.
*/
if (prev != NULL && prev->type == u8 &&
UINT32_MAX - prev->n >= count) {
prev->n += count;
continue;
}
chunk->n = count;
chunk->type = u8;
prev = chunk;
chunk++;
}
assert(chunk <= chunks + vec_count);
/*
* shrink the array in case we "packed" locals above.
* REVISIT: is this worth a realloc?
*/
if (chunk < chunks + vec_count) {
void *shrinked =
realloc(chunks, (uintptr_t)chunk - (uintptr_t)chunks);
if (shrinked != NULL) {
chunks = shrinked;
}
}
lt->localchunks = chunks;
lt->nlocals = nlocals;
#if defined(TOYWASM_USE_LOCALTYPE_CELLIDX)
Expand Down