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Zero-initialize small strings using memset

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This commit is contained in:
Richard Feldman 2020-09-16 01:18:08 -04:00
parent 8e630fc9fc
commit bec7254d92
1 changed files with 18 additions and 0 deletions
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18
compiler/gen/src/llvm/build.rs
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@ -366,6 +366,24 @@ pub fn build_exp_literal<'a, 'ctx, 'env>(
"alloca_small_str",
);
// Zero out all the bytes. If we don't do this, then
// small strings would have uninitialized bytes, which could
// cause string equality checks to fail randomly.
//
// We're running memset over *all* the bytes, even though
// the final one is about to be manually overridden, on
// the theory that LLVM will optimize the memset call
// into two instructions to move appropriately-sized
// zero integers into the appropriate locations instead
// of doing any iteration.
//
// TODO: look at the compiled output to verify this theory!
env.call_memset(
array_alloca,
ctx.i8_type().const_zero(),
env.ptr_int().const_int(env.small_str_bytes() as u64, false),
);
let final_byte = (str_literal.len() as u8) | 0b1000_0000;
let final_byte_ptr = unsafe {