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Auto merge of rust-lang#123778 - jhorstmann:optimize-upper-lower-auto…
…-vectorization, r=the8472 Improve autovectorization of to_lowercase / to_uppercase functions Refactor the code in the `convert_while_ascii` helper function to make it more suitable for auto-vectorization and also process the full ascii prefix of the string. The generic case conversion logic will only be invoked starting from the first non-ascii character. The runtime on a microbenchmark with a small ascii-only input decreases from ~55ns to ~18ns per iteration. The new implementation also reduces the amount of unsafe code and encapsulates all unsafe inside the helper function. Fixes rust-lang#123712
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tests/codegen/issues/issue-123712-str-to-lower-autovectorization.rs
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//@ only-x86_64 | ||
//@ compile-flags: -C opt-level=3 | ||
#![crate_type = "lib"] | ||
#![no_std] | ||
#![feature(str_internals)] | ||
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extern crate alloc; | ||
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/// Ensure that the ascii-prefix loop for `str::to_lowercase` and `str::to_uppercase` uses vector | ||
/// instructions. | ||
/// | ||
/// The llvm ir should be the same for all targets that support some form of simd. Only targets | ||
/// without any simd instructions would see scalarized ir. | ||
/// Unfortunately, there is no `only-simd` directive to only run this test on only such platforms, | ||
/// and using test revisions would still require the core libraries for all platforms. | ||
// CHECK-LABEL: @lower_while_ascii | ||
// CHECK: [[A:%[0-9]]] = load <16 x i8> | ||
// CHECK-NEXT: [[B:%[0-9]]] = icmp slt <16 x i8> [[A]], zeroinitializer | ||
// CHECK-NEXT: [[C:%[0-9]]] = bitcast <16 x i1> [[B]] to i16 | ||
#[no_mangle] | ||
pub fn lower_while_ascii(s: &str) -> (alloc::string::String, &str) { | ||
alloc::str::convert_while_ascii(s, u8::to_ascii_lowercase) | ||
} |