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switch to limiting the number of init/uninit chunks

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This commit is contained in:
Erik Desjardins 2022-02-19 01:17:31 -05:00
parent b7e5597491
commit d5769e9843
5 changed files with 16 additions and 26 deletions
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30
compiler/rustc_codegen_llvm/src/consts.rs
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@ -37,7 +37,7 @@ pub fn const_alloc_to_llvm<'ll>(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) ->
alloc: &'a Allocation,
range: Range<usize>,
) {
let mut chunks = alloc
let chunks = alloc
.init_mask()
.range_as_init_chunks(Size::from_bytes(range.start), Size::from_bytes(range.end));
@ -53,32 +53,20 @@ pub fn const_alloc_to_llvm<'ll>(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) ->
}
};
// Generating partially-uninit consts is limited to small allocations,
// Generating partially-uninit consts is limited to small numbers of chunks,
// to avoid the cost of generating large complex const expressions.
// For example, `[(u32, u8); 1024 * 1024]` contains uninit padding in each element,
// and would result in `{ [5 x i8] zeroinitializer, [3 x i8] undef, ...repeat 1M times... }`.
let allow_partially_uninit =
match cx.sess().opts.debugging_opts.partially_uninit_const_threshold {
Some(max) => range.len() <= max,
None => false,
};
let max = cx.sess().opts.debugging_opts.uninit_const_chunk_threshold;
let allow_uninit_chunks = chunks.clone().take(max.saturating_add(1)).count() <= max;
if allow_partially_uninit {
if allow_uninit_chunks {
llvals.extend(chunks.map(chunk_to_llval));
} else {
let llval = match (chunks.next(), chunks.next()) {
(Some(chunk), None) => {
// exactly one chunk, either fully init or fully uninit
chunk_to_llval(chunk)
}
_ => {
// partially uninit, codegen as if it was initialized
// (using some arbitrary value for uninit bytes)
let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(range);
cx.const_bytes(bytes)
}
};
llvals.push(llval);
// If this allocation contains any uninit bytes, codegen as if it was initialized
// (using some arbitrary value for uninit bytes).
let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(range);
llvals.push(cx.const_bytes(bytes));
}
}