cargo: Ensure 'perf' doesn't enable 'std' implicitly

regex-automata/Cargo.toml

@@ -44,7 +44,7 @@ perf = ["perf-inline", "perf-literal"]
 perf-inline = []
 perf-literal = ["perf-literal-substring", "perf-literal-multisubstring"]
 perf-literal-substring = ["aho-corasick?/perf-literal", "dep:memchr"]
-perf-literal-multisubstring = ["std", "dep:aho-corasick"]
+perf-literal-multisubstring = ["dep:aho-corasick"]
 
 # Enables all Unicode features. This expands if new Unicode features are added.
 unicode = [

regex-automata/src/lib.rs

@@ -451,6 +451,10 @@ useful in trying to understand what the meta regex engine is doing.
 
 ### Performance features
 
+**Note**:
+  To get performance benefits offered by the SIMD, `std` must be enabled.
+  None of the `perf-*` features will enable `std` implicitly.
+
 * **perf** - Enables all of the below features.
 * **perf-inline** - When enabled, `inline(always)` is used in (many) strategic
 locations to help performance at the expense of longer compile times and

src/lib.rs

@@ -1183,6 +1183,10 @@ default are noted.
 
 ### Performance features
 
+**Note**:
+  To get performance benefits offered by the SIMD, `std` must be enabled.
+  None of the `perf-*` features will enable `std` implicitly.
+
 * **perf** -
   Enables all performance related features except for `perf-dfa-full`. This
   feature is enabled by default is intended to cover all reasonable features