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Diffstat (limited to 'docs/UsersManual.rst')
| -rw-r--r-- | docs/UsersManual.rst | 72 |
1 files changed, 61 insertions, 11 deletions
diff --git a/docs/UsersManual.rst b/docs/UsersManual.rst index 90f16ee0d431..fc5af4ecd5b1 100644 --- a/docs/UsersManual.rst +++ b/docs/UsersManual.rst @@ -73,7 +73,7 @@ Basic Usage Intro to how to use a C compiler for newbies. compile + link compile then link debug info enabling optimizations -picking a language to use, defaults to C99 by default. Autosenses based +picking a language to use, defaults to C11 by default. Autosenses based on extension. using a makefile Command Line Options @@ -481,7 +481,7 @@ TODO: Generate this from tblgen. Define one anchor per warning group. Warn about an unusable copy constructor when binding a reference to a temporary. - This option, which defaults to on, enables warnings about binding a + This option enables warnings about binding a reference to a temporary when the temporary doesn't have a usable copy constructor. For example: @@ -531,8 +531,6 @@ control the crash diagnostics. The -fno-crash-diagnostics flag can be helpful for speeding the process of generating a delta reduced test case. -.. _opt_rpass: - Options to Emit Optimization Reports ------------------------------------ @@ -979,6 +977,8 @@ are listed below. - ``-fsanitize=function``: Indirect call of a function through a function pointer of the wrong type (Linux, C++ and x86/x86_64 only). - ``-fsanitize=integer-divide-by-zero``: Integer division by zero. + - ``-fsanitize=nonnull-attribute``: Passing null pointer as a function + parameter which is declared to never be null. - ``-fsanitize=null``: Use of a null pointer or creation of a null reference. - ``-fsanitize=object-size``: An attempt to use bytes which the @@ -988,6 +988,8 @@ are listed below. more problems at higher optimization levels. - ``-fsanitize=return``: In C++, reaching the end of a value-returning function without returning a value. + - ``-fsanitize=returns-nonnull-attribute``: Returning null pointer + from a function which is declared to never return null. - ``-fsanitize=shift``: Shift operators where the amount shifted is greater or equal to the promoted bit-width of the left hand side or less than zero, or where the left hand side is negative. For a @@ -1031,10 +1033,6 @@ are listed below. Extra features of UndefinedBehaviorSanitizer: - - ``-fno-sanitize-recover``: By default, after a sanitizer diagnoses - an issue, it will attempt to continue executing the program if there - is a reasonable behavior it can give to the faulting operation. This - option causes the program to abort instead. - ``-fsanitize-undefined-trap-on-error``: Causes traps to be emitted rather than calls to runtime libraries when a problem is detected. This option is intended for use in cases where the sanitizer runtime @@ -1054,6 +1052,17 @@ are listed below. program. The ``-fsanitize=undefined`` checks can be combined with other sanitizers. +**-f[no-]sanitize-recover=check1,check2,...** + + Controls which checks enabled by ``-fsanitize=`` flag are non-fatal. + If the check is fatal, program will halt after the first error + of this kind is detected and error report is printed. + + By default, non-fatal checks are those enabled by UndefinedBehaviorSanitizer, + except for ``-fsanitize=return`` and ``-fsanitize=unreachable``. Some + sanitizers (e.g. :doc:`AddressSanitizer`) may not support recovery, + and always crash the program after the issue is detected. + .. option:: -fno-assume-sane-operator-new Don't assume that the C++'s new operator is sane. @@ -1113,6 +1122,37 @@ are listed below. This option restricts the generated code to use general registers only. This only applies to the AArch64 architecture. +**-f[no-]max-unknown-pointer-align=[number]** + Instruct the code generator to not enforce a higher alignment than the given + number (of bytes) when accessing memory via an opaque pointer or reference. + This cap is ignored when directly accessing a variable or when the pointee + type has an explicit “aligned” attribute. + + The value should usually be determined by the properties of the system allocator. + Some builtin types, especially vector types, have very high natural alignments; + when working with values of those types, Clang usually wants to use instructions + that take advantage of that alignment. However, many system allocators do + not promise to return memory that is more than 8-byte or 16-byte-aligned. Use + this option to limit the alignment that the compiler can assume for an arbitrary + pointer, which may point onto the heap. + + This option does not affect the ABI alignment of types; the layout of structs and + unions and the value returned by the alignof operator remain the same. + + This option can be overridden on a case-by-case basis by putting an explicit + “aligned” alignment on a struct, union, or typedef. For example: + + .. code-block:: console + + #include <immintrin.h> + // Make an aligned typedef of the AVX-512 16-int vector type. + typedef __v16si __aligned_v16si __attribute__((aligned(64))); + + void initialize_vector(__aligned_v16si *v) { + // The compiler may assume that ‘v’ is 64-byte aligned, regardless of the + // value of -fmax-unknown-pointer-align. + } + Profile Guided Optimization --------------------------- @@ -1441,9 +1481,12 @@ Differences between various standard modes ------------------------------------------ clang supports the -std option, which changes what language mode clang -uses. The supported modes for C are c89, gnu89, c94, c99, gnu99 and -various aliases for those modes. If no -std option is specified, clang -defaults to gnu99 mode. +uses. The supported modes for C are c89, gnu89, c94, c99, gnu99, c11, +gnu11, and various aliases for those modes. If no -std option is +specified, clang defaults to gnu11 mode. Many C99 and C11 features are +supported in earlier modes as a conforming extension, with a warning. Use +``-pedantic-errors`` to request an error if a feature from a later standard +revision is used in an earlier mode. Differences between all ``c*`` and ``gnu*`` modes: @@ -1481,6 +1524,11 @@ Differences between ``*89`` and ``*99`` modes: in ``*89`` modes. - Some warnings are different. +Differences between ``*99`` and ``*11`` modes: + +- Warnings for use of C11 features are disabled. +- ``__STDC_VERSION__`` is defined to ``201112L`` rather than ``199901L``. + c94 mode is identical to c89 mode except that digraphs are enabled in c94 mode (FIXME: And ``__STDC_VERSION__`` should be defined!). @@ -1874,6 +1922,8 @@ Execute ``clang-cl /?`` to see a list of supported options: /WX Treat warnings as errors /w Disable all warnings /Zi Enable debug information + /Zp Set the default maximum struct packing alignment to 1 + /Zp<value> Specify the default maximum struct packing alignment /Zs Syntax-check only OPTIONS: |