bjoernager/rust
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Auto merge of #86383 - shamatar:slice_len_lowering, r=bjorn3

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Add MIR pass to lower call to `core::slice::len` into `Len` operand

During some larger experiment with range analysis I've found that code like `let l = slice.len()` produces different MIR then one found in bound checks. This optimization pass replaces terminators that are calls to `core::slice::len` with just a MIR operand and Goto terminator.

It uses some heuristics to remove the outer borrow that is made to call `core::slice::len`, but I assume it can be eliminated, just didn't find how.

Would like to express my gratitude to `@oli-obk` who helped me a lot on Zullip
This commit is contained in:
bors 2021-06-21 22:24:13 +00:00
commit 4573a4a879
8 changed files with 185 additions and 1 deletions
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2
compiler/rustc_hir/src/lang_items.rs
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@ -310,6 +310,8 @@ language_item_table! {
Try, sym::Try, try_trait, Target::Trait;
SliceLen, sym::slice_len_fn, slice_len_fn, Target::Method(MethodKind::Inherent);
// Language items from AST lowering
TryTraitFromResidual, sym::from_residual, from_residual_fn, Target::Method(MethodKind::Trait { body: false });
TryTraitFromOutput, sym::from_output, from_output_fn, Target::Method(MethodKind::Trait { body: false });