llvm-project/libc/common_libc_tuners.cmake

# ------------------------------------------------------------------------------
# Common tuning option definitions.
# ------------------------------------------------------------------------------

set(LIBC_COMMON_TUNE_OPTIONS "")

option(LIBC_UNSAFE_STRING_WIDE_READ "Functions searching for the first character in a string such as strlen will read the string as int sized blocks instead of bytes. This relies on undefined behavior and may fail on some systems, but improves performance on long strings." OFF)
if(LIBC_UNSAFE_STRING_WIDE_READ)
  if(LLVM_USE_SANITIZER)
    message(FATAL_ERROR "LIBC_UNSAFE_STRING_WIDE_READ is set at the same time as a sanitizer. LIBC_UNSAFE_STRING_WIDE_READ causes strlen and memchr to read beyond the end of their target strings, which is undefined behavior caught by sanitizers.")
  else()
    list(APPEND LIBC_COMMON_TUNE_OPTIONS "-DLIBC_COPT_UNSAFE_STRING_WIDE_READ")
    endif()
endif()
[libc] add unsafe mode to strlen The only safe way to implement strlen involves reading the string one char at a time. It is faster to read in larger blocks, but this leads to reading beyond the string boundary, which is undefined behavior. This patch adds an implementation and flag to use this fast but unsafe version of strlen. Reviewed By: sivachandra Differential Revision: https://reviews.llvm.org/D129808 2022-07-15 06:17:18 +08:00			`# ------------------------------------------------------------------------------`
			`# Common tuning option definitions.`
			`# ------------------------------------------------------------------------------`

			`set(LIBC_COMMON_TUNE_OPTIONS "")`

			`option(LIBC_UNSAFE_STRING_WIDE_READ "Functions searching for the first character in a string such as strlen will read the string as int sized blocks instead of bytes. This relies on undefined behavior and may fail on some systems, but improves performance on long strings." OFF)`
			`if(LIBC_UNSAFE_STRING_WIDE_READ)`
			`if(LLVM_USE_SANITIZER)`
			`message(FATAL_ERROR "LIBC_UNSAFE_STRING_WIDE_READ is set at the same time as a sanitizer. LIBC_UNSAFE_STRING_WIDE_READ causes strlen and memchr to read beyond the end of their target strings, which is undefined behavior caught by sanitizers.")`
			`else()`
[libc][NFC] Make tuning macros start with LIBC_COPT_ Rename preprocessor definitions that control tuning of llvm libc. Differential Revision: https://reviews.llvm.org/D143913 2023-02-13 22:52:26 +08:00			`list(APPEND LIBC_COMMON_TUNE_OPTIONS "-DLIBC_COPT_UNSAFE_STRING_WIDE_READ")`
[libc] add unsafe mode to strlen The only safe way to implement strlen involves reading the string one char at a time. It is faster to read in larger blocks, but this leads to reading beyond the string boundary, which is undefined behavior. This patch adds an implementation and flag to use this fast but unsafe version of strlen. Reviewed By: sivachandra Differential Revision: https://reviews.llvm.org/D129808 2022-07-15 06:17:18 +08:00			`endif()`
			`endif()`