forked from OSchip/llvm-project
614 lines
15 KiB
Plaintext
614 lines
15 KiB
Plaintext
=pod
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=head1 NAME
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clang - the Clang C, C++, and Objective-C compiler
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=head1 SYNOPSIS
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B<clang> [B<-c>|B<-S>|B<-E>] B<-std=>I<standard> B<-g>
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[B<-O0>|B<-O1>|B<-O2>|B<-O3>|B<-Ofast>|B<-Os>|B<-Oz>|B<-O>|B<-O4>]
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B<-W>I<warnings...> B<-pedantic>
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B<-I>I<dir...> B<-L>I<dir...>
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B<-D>I<macro[=defn]>
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B<-f>I<feature-option...>
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B<-m>I<machine-option...>
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B<-o> I<output-file>
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B<-stdlib=>I<library>
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I<input-filenames>
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=head1 DESCRIPTION
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B<clang> is a C, C++, and Objective-C compiler which encompasses preprocessing,
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parsing, optimization, code generation, assembly, and linking. Depending on
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which high-level mode setting is passed, Clang will stop before doing a full
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link. While Clang is highly integrated, it is important to understand the
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stages of compilation, to understand how to invoke it. These stages are:
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=over
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=item B<Driver>
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The B<clang> executable is actually a small driver which controls the overall
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execution of other tools such as the compiler, assembler and linker. Typically
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you do not need to interact with the driver, but you transparently use it to run
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the other tools.
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=item B<Preprocessing>
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This stage handles tokenization of the input source file, macro expansion,
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#include expansion and handling of other preprocessor directives. The output of
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this stage is typically called a ".i" (for C), ".ii" (for C++), ".mi" (for
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Objective-C) , or ".mii" (for Objective-C++) file.
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=item B<Parsing and Semantic Analysis>
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This stage parses the input file, translating preprocessor tokens into a parse
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tree. Once in the form of a parser tree, it applies semantic analysis to compute
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types for expressions as well and determine whether the code is well formed. This
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stage is responsible for generating most of the compiler warnings as well as
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parse errors. The output of this stage is an "Abstract Syntax Tree" (AST).
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=item B<Code Generation and Optimization>
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This stage translates an AST into low-level intermediate code (known as "LLVM
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IR") and ultimately to machine code. This phase is responsible for optimizing
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the generated code and handling target-specific code generation. The output of
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this stage is typically called a ".s" file or "assembly" file.
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Clang also supports the use of an integrated assembler, in which the code
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generator produces object files directly. This avoids the overhead of generating
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the ".s" file and of calling the target assembler.
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=item B<Assembler>
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This stage runs the target assembler to translate the output of the compiler
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into a target object file. The output of this stage is typically called a ".o"
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file or "object" file.
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=item B<Linker>
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This stage runs the target linker to merge multiple object files into an
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executable or dynamic library. The output of this stage is typically called an
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"a.out", ".dylib" or ".so" file.
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=back
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The Clang compiler supports a large number of options to control each of these
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stages. In addition to compilation of code, Clang also supports other tools:
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B<Clang Static Analyzer>
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The Clang Static Analyzer is a tool that scans source code to try to find bugs
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through code analysis. This tool uses many parts of Clang and is built into the
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same driver. Please see L<http://clang-analyzer.llvm.org> for more details
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on how to use the static analyzer.
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=head1 OPTIONS
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=head2 Stage Selection Options
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=over
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=item B<-E>
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Run the preprocessor stage.
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=item B<-fsyntax-only>
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Run the preprocessor, parser and type checking stages.
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=item B<-S>
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Run the previous stages as well as LLVM generation and optimization stages and
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target-specific code generation, producing an assembly file.
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=item B<-c>
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Run all of the above, plus the assembler, generating a target ".o" object file.
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=item B<no stage selection option>
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If no stage selection option is specified, all stages above are run, and the
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linker is run to combine the results into an executable or shared library.
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=back
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=head2 Language Selection and Mode Options
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=over
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=item B<-x> I<language>
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Treat subsequent input files as having type I<language>.
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=item B<-std>=I<language>
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Specify the language standard to compile for.
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=item B<-stdlib>=I<library>
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Specify the C++ standard library to use; supported options are libstdc++ and
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libc++.
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=item B<-ansi>
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Same as B<-std=c89>.
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=item B<-ObjC++>
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Treat source input files as Objective-C++ inputs.
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=item B<-ObjC>
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Treat source input files as Objective-C inputs.
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=item B<-trigraphs>
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Enable trigraphs.
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=item B<-ffreestanding>
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Indicate that the file should be compiled for a freestanding, not a hosted,
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environment.
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=item B<-fno-builtin>
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Disable special handling and optimizations of builtin functions like strlen and
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malloc.
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=item B<-fmath-errno>
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Indicate that math functions should be treated as updating errno.
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=item B<-fpascal-strings>
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Enable support for Pascal-style strings with "\pfoo".
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=item B<-fms-extensions>
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Enable support for Microsoft extensions.
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=item B<-fmsc-version=>
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Set _MSC_VER. Defaults to 1300 on Windows. Not set otherwise.
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=item B<-fborland-extensions>
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Enable support for Borland extensions.
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=item B<-fwritable-strings>
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Make all string literals default to writable. This disables uniquing of
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strings and other optimizations.
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=item B<-flax-vector-conversions>
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Allow loose type checking rules for implicit vector conversions.
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=item B<-fblocks>
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Enable the "Blocks" language feature.
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=item B<-fobjc-gc-only>
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Indicate that Objective-C code should be compiled in GC-only mode, which only
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works when Objective-C Garbage Collection is enabled.
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=item B<-fobjc-gc>
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Indicate that Objective-C code should be compiled in hybrid-GC mode, which works
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with both GC and non-GC mode.
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=item B<-fobjc-abi-version>=I<version>
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Select the Objective-C ABI version to use. Available versions are 1 (legacy
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"fragile" ABI), 2 (non-fragile ABI 1), and 3 (non-fragile ABI 2).
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=item B<-fobjc-nonfragile-abi-version>=I<version>
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Select the Objective-C non-fragile ABI version to use by default. This will only
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be used as the Objective-C ABI when the non-fragile ABI is enabled (either via
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-fobjc-nonfragile-abi, or because it is the platform default).
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=item B<-fobjc-nonfragile-abi>
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Enable use of the Objective-C non-fragile ABI. On platforms for which this is
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the default ABI, it can be disabled with B<-fno-objc-nonfragile-abi>.
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=back
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=head2 Target Selection Options
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Clang fully supports cross compilation as an inherent part of its design.
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Depending on how your version of Clang is configured, it may have support for
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a number of cross compilers, or may only support a native target.
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=over
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=item B<-arch> I<architecture>
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Specify the architecture to build for.
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=item B<-mmacosx-version-min>=I<version>
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When building for Mac OS X, specify the minimum version supported by your
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application.
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=item B<-miphoneos-version-min>
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When building for iPhone OS, specify the minimum version supported by your
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application.
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=item B<-march>=I<cpu>
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Specify that Clang should generate code for a specific processor family member
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and later. For example, if you specify -march=i486, the compiler is allowed to
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generate instructions that are valid on i486 and later processors, but which
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may not exist on earlier ones.
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=back
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=head2 Code Generation Options
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=over
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=item B<-O0> B<-O1> B<-O2> B<-O3> B<-Ofast> B<-Os> B<-Oz> B<-O> B<-O4>
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Specify which optimization level to use:
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=over
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=item B<-O0>
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Means "no optimization": this level compiles the fastest and
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generates the most debuggable code.
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=item B<-O1>
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Somewhere between B<-O0> and B<-O2>.
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=item B<-O2>
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Moderate level of optimization which enables most optimizations.
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=item B<-O3>
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Like B<-O2>, except that it enables optimizations that take longer to perform
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or that may generate larger code (in an attempt to make the program run faster).
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=item B<-Ofast>
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Enables all the optimizations from B<-O3> along with other aggressive
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optimizations that may violate strict compliance with language standards.
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=item B<-Os>
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Like B<-O2> with extra optimizations to reduce code size.
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=item B<-Oz>
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Like B<-Os> (and thus B<-O2>), but reduces code size further.
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=item B<-O>
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Equivalent to B<-O2>.
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=item B<-O4> and higher
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Currently equivalent to B<-O3>
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=back
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=item B<-g>
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Generate debug information. Note that Clang debug information works best at
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B<-O0>.
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=item B<-fstandalone-debug> B<-fno-standalone-debug>
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Clang supports a number of optimizations to reduce the size of debug
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information in the binary. They work based on the assumption that the
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debug type information can be spread out over multiple compilation
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units. For instance, Clang will not emit type definitions for types
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that are not needed by a module and could be replaced with a forward
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declaration. Further, Clang will only emit type info for a dynamic
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C++ class in the module that contains the vtable for the class.
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The B<-fstandalone-debug> option turns off these optimizations. This
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is useful when working with 3rd-party libraries that don't come with
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debug information. Note that Clang will never emit type information
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for types that are not referenced at all by the program.
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=item B<-fexceptions>
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Enable generation of unwind information, this allows exceptions to be thrown
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through Clang compiled stack frames. This is on by default in x86-64.
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=item B<-ftrapv>
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Generate code to catch integer overflow errors. Signed integer overflow is
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undefined in C, with this flag, extra code is generated to detect this and abort
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when it happens.
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=item B<-fvisibility>
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This flag sets the default visibility level.
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=item B<-fcommon>
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This flag specifies that variables without initializers get common linkage. It
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can be disabled with B<-fno-common>.
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=item B<-ftls-model>
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Set the default thread-local storage (TLS) model to use for thread-local
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variables. Valid values are: "global-dynamic", "local-dynamic", "initial-exec"
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and "local-exec". The default is "global-dynamic". The default model can be
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overridden with the tls_model attribute. The compiler will try to choose a more
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efficient model if possible.
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=item B<-flto> B<-emit-llvm>
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Generate output files in LLVM formats, suitable for link time optimization. When
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used with B<-S> this generates LLVM intermediate language assembly files,
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otherwise this generates LLVM bitcode format object files (which may be passed
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to the linker depending on the stage selection options).
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=cut
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##=item B<-fnext-runtime> B<-fobjc-nonfragile-abi> B<-fgnu-runtime>
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##These options specify which Objective-C runtime the code generator should
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##target. FIXME: we don't want people poking these generally.
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=pod
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=back
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=head2 Driver Options
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=over
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=item B<-###>
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Print (but do not run) the commands to run for this compilation.
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=item B<--help>
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Display available options.
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=item B<-Qunused-arguments>
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Don't emit warning for unused driver arguments.
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=item B<-Wa,>I<args>
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Pass the comma separated arguments in I<args> to the assembler.
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=item B<-Wl,>I<args>
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Pass the comma separated arguments in I<args> to the linker.
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=item B<-Wp,>I<args>
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Pass the comma separated arguments in I<args> to the preprocessor.
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=item B<-Xanalyzer> I<arg>
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Pass I<arg> to the static analyzer.
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=item B<-Xassembler> I<arg>
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Pass I<arg> to the assembler.
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=item B<-Xlinker> I<arg>
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Pass I<arg> to the linker.
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=item B<-Xpreprocessor> I<arg>
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Pass I<arg> to the preprocessor.
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=item B<-o> I<file>
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Write output to I<file>.
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=item B<-print-file-name>=I<file>
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Print the full library path of I<file>.
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=item B<-print-libgcc-file-name>
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Print the library path for "libgcc.a".
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=item B<-print-prog-name>=I<name>
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Print the full program path of I<name>.
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=item B<-print-search-dirs>
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Print the paths used for finding libraries and programs.
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=item B<-save-temps>
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Save intermediate compilation results.
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=item B<-integrated-as> B<-no-integrated-as>
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Used to enable and disable, respectively, the use of the integrated
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assembler. Whether the integrated assembler is on by default is target
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dependent.
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=item B<-time>
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Time individual commands.
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=item B<-ftime-report>
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Print timing summary of each stage of compilation.
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=item B<-v>
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Show commands to run and use verbose output.
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=back
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=head2 Diagnostics Options
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=over
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=item B<-fshow-column>
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B<-fshow-source-location>
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B<-fcaret-diagnostics>
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B<-fdiagnostics-fixit-info>
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B<-fdiagnostics-parseable-fixits>
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B<-fdiagnostics-print-source-range-info>
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B<-fprint-source-range-info>
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B<-fdiagnostics-show-option>
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B<-fmessage-length>
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These options control how Clang prints out information about diagnostics (errors
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and warnings). Please see the Clang User's Manual for more information.
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=back
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=head2 Preprocessor Options
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=over
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=item B<-D>I<macroname=value>
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Adds an implicit #define into the predefines buffer which is read before the
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source file is preprocessed.
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=item B<-U>I<macroname>
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Adds an implicit #undef into the predefines buffer which is read before the
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source file is preprocessed.
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=item B<-include> I<filename>
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Adds an implicit #include into the predefines buffer which is read before the
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source file is preprocessed.
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=item B<-I>I<directory>
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Add the specified directory to the search path for include files.
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=item B<-F>I<directory>
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Add the specified directory to the search path for framework include files.
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=item B<-nostdinc>
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Do not search the standard system directories or compiler builtin directories
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for include files.
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=item B<-nostdlibinc>
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Do not search the standard system directories for include files, but do search
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compiler builtin include directories.
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=item B<-nobuiltininc>
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Do not search clang's builtin directory for include files.
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=cut
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## TODO, but do we really want people using this stuff?
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#=item B<-idirafter>I<directory>
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#=item B<-iquote>I<directory>
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#=item B<-isystem>I<directory>
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#=item B<-iprefix>I<directory>
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#=item B<-iwithprefix>I<directory>
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#=item B<-iwithprefixbefore>I<directory>
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#=item B<-isysroot>
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=pod
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=back
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=cut
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### TODO someday.
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#=head2 Warning Control Options
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#=over
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#=back
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#=head2 Code Generation and Optimization Options
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#=over
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#=back
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#=head2 Assembler Options
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#=over
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#=back
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#=head2 Linker Options
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#=over
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#=back
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#=head2 Static Analyzer Options
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#=over
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#=back
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=pod
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=head1 ENVIRONMENT
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=over
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=item B<TMPDIR>, B<TEMP>, B<TMP>
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These environment variables are checked, in order, for the location to
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write temporary files used during the compilation process.
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=item B<CPATH>
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If this environment variable is present, it is treated as a delimited
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list of paths to be added to the default system include path list. The
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delimiter is the platform dependent delimitor, as used in the I<PATH>
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environment variable.
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Empty components in the environment variable are ignored.
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=item B<C_INCLUDE_PATH>, B<OBJC_INCLUDE_PATH>, B<CPLUS_INCLUDE_PATH>,
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B<OBJCPLUS_INCLUDE_PATH>
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These environment variables specify additional paths, as for CPATH,
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which are only used when processing the appropriate language.
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=item B<MACOSX_DEPLOYMENT_TARGET>
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If -mmacosx-version-min is unspecified, the default deployment target
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is read from this environment variable. This option only affects darwin
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targets.
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=back
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=head1 BUGS
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To report bugs, please visit L<http://llvm.org/bugs/>. Most bug reports should
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include preprocessed source files (use the B<-E> option) and the full output of
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the compiler, along with information to reproduce.
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=head1 SEE ALSO
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as(1), ld(1)
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=head1 AUTHOR
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Maintained by the Clang / LLVM Team (L<http://clang.llvm.org>).
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=cut
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