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wasm: Generate Str literals with capacity

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Brian Carroll 2022-03-09 08:26:15 +00:00
parent 19c46916d9
commit 0c6fef0ba3
1 changed files with 22 additions and 8 deletions
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30
compiler/gen_wasm/src/backend.rs
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@ -654,30 +654,44 @@ impl<'a> WasmBackend<'a> {
location.local_and_offset(self.storage.stack_frame_pointer);
let len = string.len();
if len < 8 {
let mut stack_mem_bytes = [0; 8];
stack_mem_bytes[0..len].clone_from_slice(string.as_bytes());
stack_mem_bytes[7] = 0x80 | (len as u8);
let str_as_int = i64::from_le_bytes(stack_mem_bytes);
if len < 12 {
// Construct the bytes of the small string
let mut bytes = [0; 12];
bytes[0..len].clone_from_slice(string.as_bytes());
bytes[11] = 0x80 | (len as u8);
// Write all 8 bytes at once using an i64
// Str is normally two i32's, but in this special case, we can get away with fewer instructions
// Transform into two integers, to minimise number of instructions
let bytes_split: &([u8; 8], [u8; 4]) = unsafe { std::mem::transmute(&bytes) };
let int64 = i64::from_le_bytes(bytes_split.0);
let int32 = i32::from_le_bytes(bytes_split.1);
// Write the integers to memory
self.code_builder.get_local(local_id);
self.code_builder.i64_const(str_as_int);
self.code_builder.i64_const(int64);
self.code_builder.i64_store(Align::Bytes4, offset);
self.code_builder.get_local(local_id);
self.code_builder.i32_const(int32);
self.code_builder.i32_store(Align::Bytes4, offset + 8);
} else {
let bytes = string.as_bytes();
let (linker_sym_index, elements_addr) =
self.store_bytes_in_data_section(bytes, sym);
// ptr
self.code_builder.get_local(local_id);
self.code_builder
.i32_const_mem_addr(elements_addr, linker_sym_index);
self.code_builder.i32_store(Align::Bytes4, offset);
// len
self.code_builder.get_local(local_id);
self.code_builder.i32_const(string.len() as i32);
self.code_builder.i32_store(Align::Bytes4, offset + 4);
// capacity
self.code_builder.get_local(local_id);
self.code_builder.i32_const(string.len() as i32);
self.code_builder.i32_store(Align::Bytes4, offset + 8);
};
}
_ => invalid_error(),