…cialization, r=Darksonn
iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>
`StepBy<Range<{integer}>>` already has a fast path that converts the range
into a yield-count before iteration, avoiding per-step overflow checks and
enabling better loop structure for the optimizer. `StepBy<RangeIter<{integer}>>`
did not benefit from the same optimization even though `RangeIter<T>` is a thin
newtype wrapper around `legacy::Range<T>`.
## Changes
- `library/core/src/range/iter.rs`: make `RangeIter<A>.0` `pub(crate)` so the
  step_by adapter can access the inner legacy range's start/end fields.
- `library/core/src/iter/adapters/step_by.rs`: add `spec_int_ranges_new!` and
  `spec_int_ranges_new_r!` macros that mirror the existing `spec_int_ranges!` /
  `spec_int_ranges_r!` implementations. Forward specialization covers `u8 u16
  u32 u64 usize` (pointer-width-gated for u32/u64); backward specialization is
  limited to `u8 u16 usize` since `RangeIter<u32>` / `RangeIter<u64>` do not
  implement `ExactSizeIterator`.
- `library/coretests/tests/iter/adapters/step_by.rs`: add
  `test_step_by_new_range_iter` covering forward, backward, and interleaved
  iteration via the new-range iterator.
## Motivation
Fixes rust-lang#157754. The inner loop for `core::range::Range::from(0..n).into_iter().step_by(2)` currently generates noticeably worse assembly than the equivalent `(0..n).step_by(2)` because specialization did not cover `RangeIter`.
r? libs

…uwer
Rollup of 25 pull requests
Successful merges:
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158404 (trait_solver: normalize next-gen region constraints)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159785 (Share _Unwind_Exception definition between native and wasm)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)

…uwer
Rollup of 25 pull requests
Successful merges:
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158404 (trait_solver: normalize next-gen region constraints)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159785 (Share _Unwind_Exception definition between native and wasm)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)

…uwer
Rollup of 25 pull requests
Successful merges:
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158404 (trait_solver: normalize next-gen region constraints)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159785 (Share _Unwind_Exception definition between native and wasm)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)

…cialization, r=Darksonn
iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>
`StepBy<Range<{integer}>>` already has a fast path that converts the range
into a yield-count before iteration, avoiding per-step overflow checks and
enabling better loop structure for the optimizer. `StepBy<RangeIter<{integer}>>`
did not benefit from the same optimization even though `RangeIter<T>` is a thin
newtype wrapper around `legacy::Range<T>`.
## Changes
- `library/core/src/range/iter.rs`: make `RangeIter<A>.0` `pub(crate)` so the
  step_by adapter can access the inner legacy range's start/end fields.
- `library/core/src/iter/adapters/step_by.rs`: add `spec_int_ranges_new!` and
  `spec_int_ranges_new_r!` macros that mirror the existing `spec_int_ranges!` /
  `spec_int_ranges_r!` implementations. Forward specialization covers `u8 u16
  u32 u64 usize` (pointer-width-gated for u32/u64); backward specialization is
  limited to `u8 u16 usize` since `RangeIter<u32>` / `RangeIter<u64>` do not
  implement `ExactSizeIterator`.
- `library/coretests/tests/iter/adapters/step_by.rs`: add
  `test_step_by_new_range_iter` covering forward, backward, and interleaved
  iteration via the new-range iterator.
## Motivation
Fixes rust-lang#157754. The inner loop for `core::range::Range::from(0..n).into_iter().step_by(2)` currently generates noticeably worse assembly than the equivalent `(0..n).step_by(2)` because specialization did not cover `RangeIter`.
r? libs

…uwer
Rollup of 25 pull requests
Successful merges:
 - #159825 (codegen: handle OperandValue::Uninit in codegen_return_terminator)
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158404 (trait_solver: normalize next-gen region constraints)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)

…uwer
Rollup of 25 pull requests
Successful merges:
 - #159825 (codegen: handle OperandValue::Uninit in codegen_return_terminator)
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158404 (trait_solver: normalize next-gen region constraints)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)

…cialization, r=Darksonn
iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>
`StepBy<Range<{integer}>>` already has a fast path that converts the range
into a yield-count before iteration, avoiding per-step overflow checks and
enabling better loop structure for the optimizer. `StepBy<RangeIter<{integer}>>`
did not benefit from the same optimization even though `RangeIter<T>` is a thin
newtype wrapper around `legacy::Range<T>`.
## Changes
- `library/core/src/range/iter.rs`: make `RangeIter<A>.0` `pub(crate)` so the
  step_by adapter can access the inner legacy range's start/end fields.
- `library/core/src/iter/adapters/step_by.rs`: add `spec_int_ranges_new!` and
  `spec_int_ranges_new_r!` macros that mirror the existing `spec_int_ranges!` /
  `spec_int_ranges_r!` implementations. Forward specialization covers `u8 u16
  u32 u64 usize` (pointer-width-gated for u32/u64); backward specialization is
  limited to `u8 u16 usize` since `RangeIter<u32>` / `RangeIter<u64>` do not
  implement `ExactSizeIterator`.
- `library/coretests/tests/iter/adapters/step_by.rs`: add
  `test_step_by_new_range_iter` covering forward, backward, and interleaved
  iteration via the new-range iterator.
## Motivation
Fixes rust-lang#157754. The inner loop for `core::range::Range::from(0..n).into_iter().step_by(2)` currently generates noticeably worse assembly than the equivalent `(0..n).step_by(2)` because specialization did not cover `RangeIter`.
r? libs

Rollup of 25 pull requests
Successful merges:
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #152439 (Fix typos and grammar in library documentation)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)
 - #159878 (bootstrap: Remove obsolete option `build.compiletest-use-stage0-libtest`)

Rollup of 25 pull requests
Successful merges:
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #152439 (Fix typos and grammar in library documentation)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)
 - #159878 (bootstrap: Remove obsolete option `build.compiletest-use-stage0-libtest`)

Rollup of 25 pull requests
Successful merges:
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #152439 (Fix typos and grammar in library documentation)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)
 - #159878 (bootstrap: Remove obsolete option `build.compiletest-use-stage0-libtest`)

Rollup of 25 pull requests
Successful merges:
 - #138618 (Support using const pointers in asm `const` operand)
 - #157962 (Lower paths to functions in const args as ConstKind::Error)
 - #158709 (rustdoc: warn on improperly interleaved HTML/MD)
 - #159174 (Fix implicit_provenance_casts warnings on Xous)
 - #159179 (enable `unreachable_cfg_select_predicates` lint as part of `unused` lint group)
 - #159518 (iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>)
 - #159673 (bootstrap: forward -fdebug-prefix-map when using cc)
 - #159700 (Split non-local `semicolon_in_expressions_from_macros` into a separate lint)
 - #159720 (document #[global_allocator] constraints)
 - #159732 (optimization: don't look for diagnostic/canonical items without rustc_attrs enabled)
 - #159738 (implement `CovariantUnsafeCell`)
 - #159740 (reuse regular exported_non_generic_symbols logic in Miri)
 - #159780 (check `extern "custom"` function pointers)
 - #159786 (rustdoc-js: ignore editor temp files in test folder discovery)
 - #159819 (std::sync::poison: disable auto_cfg on PoisonError::new)
 - #152439 (Fix typos and grammar in library documentation)
 - #155388 (stepping into where-clauses during normalization may be productive)
 - #155914 (when bailing on ambiguity, don't force other results to ambig)
 - #159204 (Add support to caller_location to rustc_public)
 - #159439 (Fix(lib/fs/win): Fall back on Win32 delete for `Dir::remove_file`)
 - #159676 (Update wasm-component-ld to 0.5.27)
 - #159695 (proc_macro: Fix cfg_attr inner attrs in file modules)
 - #159730 (allow accessing the contents of UnsafeCell without going through get)
 - #159809 (Avoid `#[target_features]`)
 - #159878 (bootstrap: Remove obsolete option `build.compiletest-use-stage0-libtest`)

Rollup merge of #159518 - Lfan-ke:fix/step-by-range-iter-specialization, r=Darksonn
iter: extend step_by specialization to cover StepBy<RangeIter<{integer}>>
`StepBy<Range<{integer}>>` already has a fast path that converts the range
into a yield-count before iteration, avoiding per-step overflow checks and
enabling better loop structure for the optimizer. `StepBy<RangeIter<{integer}>>`
did not benefit from the same optimization even though `RangeIter<T>` is a thin
newtype wrapper around `legacy::Range<T>`.
## Changes
- `library/core/src/range/iter.rs`: make `RangeIter<A>.0` `pub(crate)` so the
  step_by adapter can access the inner legacy range's start/end fields.
- `library/core/src/iter/adapters/step_by.rs`: add `spec_int_ranges_new!` and
  `spec_int_ranges_new_r!` macros that mirror the existing `spec_int_ranges!` /
  `spec_int_ranges_r!` implementations. Forward specialization covers `u8 u16
  u32 u64 usize` (pointer-width-gated for u32/u64); backward specialization is
  limited to `u8 u16 usize` since `RangeIter<u32>` / `RangeIter<u64>` do not
  implement `ExactSizeIterator`.
- `library/coretests/tests/iter/adapters/step_by.rs`: add
  `test_step_by_new_range_iter` covering forward, backward, and interleaved
  iteration via the new-range iterator.
## Motivation
Fixes #157754. The inner loop for `core::range::Range::from(0..n).into_iter().step_by(2)` currently generates noticeably worse assembly than the equivalent `(0..n).step_by(2)` because specialization did not cover `RangeIter`.
r? libs