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Rollup merge of #69922 - RalfJung:less-intrinsic, r=oli-obk

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implement zeroed and uninitialized with MaybeUninit

This is the second attempt of doing such a change (first PR: https://github.com/rust-lang/rust/pull/62150). The last change [got reverted](https://github.com/rust-lang/rust/pull/63343) because it [caused](https://github.com/rust-lang/rust/issues/62825) some [issues](https://github.com/rust-lang/rust/issues/52898#issuecomment-512182438) in [code that incorrectly used these functions](https://github.com/erlepereira/x11-rs/issues/99).

Since then, the [problematic code has been fixed](https://github.com/erlepereira/x11-rs/pull/101), and rustc [gained a lint](https://github.com/rust-lang/rust/pull/63346) that is able to detect many misuses of these functions statically and a [dynamic check that panics](https://github.com/rust-lang/rust/pull/66059) instead of causing UB for some incorrect uses.

Fixes https://github.com/rust-lang/rust/issues/62825
This commit is contained in:
Mazdak Farrokhzad 2020-03-17 12:16:16 +01:00 • committed by GitHub
commit 7a7ca8238f
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10 changed files with 18 additions and 113 deletions
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22
src/librustc_codegen_llvm/intrinsic.rs
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@ -195,26 +195,8 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
.unwrap();
OperandRef::from_const(self, ty_name, ret_ty).immediate_or_packed_pair(self)
}
"init" => {
let ty = substs.type_at(0);
if !self.layout_of(ty).is_zst() {
// Just zero out the stack slot.
// If we store a zero constant, LLVM will drown in vreg allocation for large
// data structures, and the generated code will be awful. (A telltale sign of
// this is large quantities of `mov [byte ptr foo],0` in the generated code.)
memset_intrinsic(
self,
false,
ty,
llresult,
self.const_u8(0),
self.const_usize(1),
);
}
return;
}
// Effectively no-ops
"uninit" | "forget" => {
// Effectively no-op
"forget" => {
return;
}
"offset" => {