clang及参数和生成中间代码

    Clang是一个C语言、C++、Objective-C、Objective-C++语言的轻量级编译器。源代码发布于BSD协议下。Clang将支持其普通lambda表达式、返回类型的简化处理以及更好的处理constexpr关键字。
    Clang是一个C++编写、基于LLVM、发布于LLVM BSD许可证下的C/C++/Objective-C/Objective-C++编译器。它与GNU C语言规范几乎完全兼容(当然,也有部分不兼容的内容,包括编译命令选项也会有点差异),并在此基础上增加了额外的语法特性,比如C函数重载(通过__attribute__((overloadable))来修饰函数),其目标(之一)就是超越GCC。

Clang 的开发背景
由于 GNU 编译器套装 (GCC) 系统庞大,而且 Apple 大量使用的 Objective-C 在 GCC 中优先级较低,同时 GCC 作为一个纯粹的编译系统,与 IDE 配合并不优秀,Apple 决定从零开始写 C family 的前端,也就是基于 LLVM 的 Clang 了。Clang 由 Apple 公司开发,源代码授权使用 BSD 的开源授权。

相比于 GCC,Clang 具有如下优点:
编译速度快:在某些平台上,Clang 的编译速度显著的快过 GCC。
占用内存小:Clang 生成的 AST 所占用的内存是 GCC 的五分之一左右。
模块化设计:Clang 采用基于库的模块化设计,易于 IDE 集成及其他用途的重用。
诊断信息可读性强:在编译过程中,Clang 创建并保留了大量详细的元数据 (metadata),有利于调试和错误报告。
设计清晰简单,容易理解,易于扩展增强。与代码基础古老的 GCC 相比,学习曲线平缓。

当前 Clang 还处在不断完善过程中,相比于 GCC, Clang 在以下方面还需要加强:
支持更多语言:GCC 除了支持 C/C++/Objective-C, 还支持 Fortran/Pascal/Java/Ada/Go 和其他语言。Clang 目前支持的语言有 C/C++/Objective-C/Objective-C++。
加强对 C++ 的支持:Clang 对 C++ 的支持依然落后于 GCC,Clang 还需要加强对 C++ 提供全方位支持。
支持更多平台:GCC 流行的时间比较长,已经被广泛使用,对各种平台的支持也很完备。Clang 目前支持的平台有 Linux/Windows/Mac OS。
命令行

zzx:clang zzx$ clang -help
OVERVIEW: clang LLVM compiler

USAGE: clang [options] 

OPTIONS:
  -###                    Print (but do not run) the commands to run for this compilation
  --analyzer-output 
                          Static analyzer report output format (html|plist|plist-multi-file|plist-html|text).
  --analyze               Run the static analyzer
  -arcmt-migrate-emit-errors
                          Emit ARC errors even if the migrator can fix them
  -arcmt-migrate-report-output 
                          Output path for the plist report
  -cl-denorms-are-zero    OpenCL only. Allow denormals to be flushed to zero.
  -cl-fast-relaxed-math   OpenCL only. Sets -cl-finite-math-only and -cl-unsafe-math-optimizations, and defines __FAST_RELAXED_MATH__.
  -cl-finite-math-only    OpenCL only. Allow floating-point optimizations that assume arguments and results are not NaNs or +-Inf.
  -cl-fp32-correctly-rounded-divide-sqrt
                          OpenCL only. Specify that single precision floating-point divide and sqrt used in the program source are correctly rounded.
  -cl-kernel-arg-info     OpenCL only. Generate kernel argument metadata.
  -cl-mad-enable          OpenCL only. Allow use of less precise MAD computations in the generated binary.
  -cl-no-signed-zeros     OpenCL only. Allow use of less precise no signed zeros computations in the generated binary.
  -cl-opt-disable         OpenCL only. This option disables all optimizations. By default optimizations are enabled.
  -cl-single-precision-constant
                          OpenCL only. Treat double precision floating-point constant as single precision constant.
  -cl-std=         OpenCL language standard to compile for.
  -cl-strict-aliasing     OpenCL only. This option is added for compatibility with OpenCL 1.0.
  -cl-unsafe-math-optimizations
                          OpenCL only. Allow unsafe floating-point optimizations.  Also implies -cl-no-signed-zeros and -cl-mad-enable.
  --cuda-compile-host-device
                          Compile CUDA code for both host and device (default).  Has no effect on non-CUDA compilations.
  --cuda-device-only      Compile CUDA code for device only
  --cuda-gpu-arch= CUDA GPU architecture (e.g. sm_35).  May be specified more than once.
  --cuda-host-only        Compile CUDA code for host only.  Has no effect on non-CUDA compilations.
  --cuda-noopt-device-debug
                          Enable device-side debug info generation. Disables ptxas optimizations.
  --cuda-path=     CUDA installation path
  -cxx-isystem 
                          Add directory to the C++ SYSTEM include search path
  -c                      Only run preprocess, compile, and assemble steps
  -dD                     Print macro definitions in -E mode in addition to normal output
  -dependency-dot  Filename to write DOT-formatted header dependencies to
  -dependency-file 
                          Filename (or -) to write dependency output to
  -dM                     Print macro definitions in -E mode instead of normal output
  -emit-ast               Emit Clang AST files for source inputs
  -emit-llvm              Use the LLVM representation for assembler and object files
  -E                      Only run the preprocessor
  -faltivec               Enable AltiVec vector initializer syntax
  -fansi-escape-codes     Use ANSI escape codes for diagnostics
  -fapinotes-cache-path=
                          Specify the API notes cache path
  -fapinotes-modules      Enable module-based external API notes support
  -fapinotes-swift-version=
                          Specify the Swift version to use when filtering API notes
  -fapinotes              Enable external API notes support
  -fapple-kext            Use Apple's kernel extensions ABI
  -fapple-pragma-pack     Enable Apple gcc-compatible #pragma pack handling
  -fapplication-extension Restrict code to those available for App Extensions
  -fblocks                Enable the 'blocks' language feature
  -fborland-extensions    Accept non-standard constructs supported by the Borland compiler
  -fbuild-session-file=
                          Use the last modification time of  as the build session timestamp
  -fbuild-session-timestamp= in seconds>
                          Time when the current build session started
  -fcolor-diagnostics     Use colors in diagnostics
  -fcomment-block-commands=
                          Treat each comma separated argument in  as a documentation comment block command
  -fcoverage-mapping      Generate coverage mapping to enable code coverage analysis
  -fcuda-approx-transcendentals
                          Use approximate transcendental functions
  -fcuda-flush-denormals-to-zero
                          Flush denormal floating point values to zero in CUDA device mode.
  -fcxx-exceptions        Enable C++ exceptions
  -fdata-sections         Place each data in its own section (ELF Only)
  -fdebug-prefix-map=
                          remap file source paths in debug info
  -fdebug-types-section   Place debug types in their own section (ELF Only)
  -fdeclspec              Allow __declspec as a keyword
  -fdelayed-template-parsing
                          Parse templated function definitions at the end of the translation unit
  -fdiagnostics-parseable-fixits
                          Print fix-its in machine parseable form
  -fdiagnostics-print-source-range-info
                          Print source range spans in numeric form
  -fdiagnostics-show-hotness
                          Enable profile hotness information in diagnostic line
  -fdiagnostics-show-note-include-stack
                          Display include stacks for diagnostic notes
  -fdiagnostics-show-option
                          Print option name with mappable diagnostics
  -fdiagnostics-show-template-tree
                          Print a template comparison tree for differing templates
  -fdollars-in-identifiers
                          Allow '$' in identifiers
  -fembed-bitcode-marker  Embed placeholder LLVM IR data as a marker
  -fembed-bitcode=                          Embed LLVM bitcode (option: off, all, bitcode, marker)
  -fembed-bitcode         Embed LLVM IR bitcode as data
  -femit-all-decls        Emit all declarations, even if unused
  -femulated-tls          Use emutls functions to access thread_local variables
  -fexceptions            Enable support for exception handling
  -ffast-math             Allow aggressive, lossy floating-point optimizations
  -ffixed-r9              Reserve the r9 register (ARM only)
  -ffixed-x18             Reserve the x18 register (AArch64 only)
  -ffp-contract=   Form fused FP ops (e.g. FMAs): fast (everywhere) | on (according to FP_CONTRACT pragma, default) | off (never fuse)
  -ffreestanding          Assert that the compilation takes place in a freestanding environment
  -ffunction-sections     Place each function in its own section (ELF Only)
  -fgnu-keywords          Allow GNU-extension keywords regardless of language standard
  -fgnu-runtime           Generate output compatible with the standard GNU Objective-C runtime
  -fgnu89-inline          Use the gnu89 inline semantics
  -fimplicit-module-maps  Implicitly search the file system for module map files.
  -finline-functions      Inline suitable functions
  -finline-hint-functions Inline functions wich are (explicitly or implicitly) marked inline
  -finstrument-functions  Generate calls to instrument function entry and exit
  -fintegrated-as         Enable the integrated assembler
  -flto-jobs=      Controls the backend parallelism of -flto=thin (default of 0 means the number of threads will be derived from the number of CPUs detected)
  -flto=           Set LTO mode to either 'full' or 'thin'
  -flto                   Enable LTO in 'full' mode
  -fmath-errno            Require math functions to indicate errors by setting errno
  -fmax-type-align=
                          Specify the maximum alignment to enforce on pointers lacking an explicit alignment
  -fmodule-file=    Load this precompiled module file
  -fmodule-map-file=
                          Load this module map file
  -fmodule-name=    Specify the name of the module to build
  -fmodules-cache-path=
                          Specify the module cache path
  -fmodules-decluse       Require declaration of modules used within a module
  -fmodules-disable-diagnostic-validation
                          Disable validation of the diagnostic options when loading the module
  -fmodules-ignore-macro=
                          Ignore the definition of the given macro when building and loading modules
  -fmodules-prune-after=
                          Specify the interval (in seconds) after which a module file will be considered unused
  -fmodules-prune-interval=
                          Specify the interval (in seconds) between attempts to prune the module cache
  -fmodules-search-all    Search even non-imported modules to resolve references
  -fmodules-strict-decluse
                          Like -fmodules-decluse but requires all headers to be in modules
  -fmodules-user-build-path 
                          Specify the module user build path
  -fmodules-validate-once-per-build-session
                          Don't verify input files for the modules if the module has been successfully validated or loaded during this build session
  -fmodules-validate-system-headers
                          Validate the system headers that a module depends on when loading the module
  -fmodules               Enable the 'modules' language feature
  -fms-compatibility-version=
                          Dot-separated value representing the Microsoft compiler version number to report in _MSC_VER (0 = don't define it (default))
  -fms-compatibility      Enable full Microsoft Visual C++ compatibility
  -fms-extensions         Accept some non-standard constructs supported by the Microsoft compiler
  -fmsc-version=   Microsoft compiler version number to report in _MSC_VER (0 = don't define it (default))
  -fno-access-control     Disable C++ access control
  -fno-apinotes-modules   Disable module-based external API notes support
  -fno-apinotes           Disable external API notes support
  -fno-assume-sane-operator-new
                          Don't assume that C++'s global operator new can't alias any pointer
  -fno-autolink           Disable generation of linker directives for automatic library linking
  -fno-builtin-    Disable implicit builtin knowledge of a specific function
  -fno-builtin            Disable implicit builtin knowledge of functions
  -fno-common             Compile common globals like normal definitions
  -fno-constant-cfstrings Disable creation of CodeFoundation-type constant strings
  -fno-coverage-mapping   Disable code coverage analysis
  -fno-declspec           Disallow __declspec as a keyword
  -fno-diagnostics-fixit-info
                          Do not include fixit information in diagnostics
  -fno-dollars-in-identifiers
                          Disallow '$' in identifiers
  -fno-elide-constructors Disable C++ copy constructor elision
  -fno-elide-type         Do not elide types when printing diagnostics
  -fno-gnu-inline-asm     Disable GNU style inline asm
  -fno-integrated-as      Disable the integrated assembler
  -fno-jump-tables        Do not use jump tables for lowering switches
  -fno-lax-vector-conversions
                          Disallow implicit conversions between vectors with a different number of elements or different element types
  -fno-lto                Disable LTO mode (default)
  -fno-merge-all-constants
                          Disallow merging of constants
  -fno-objc-infer-related-result-type
                          do not infer Objective-C related result type based on method family
  -fno-operator-names     Do not treat C++ operator name keywords as synonyms for operators
  -fno-preserve-as-comments
                          Do not preserve comments in inline assembly
  -fno-profile-generate   Disable generation of profile instrumentation.
  -fno-profile-instr-generate
                          Disable generation of profile instrumentation.
  -fno-profile-instr-use  Disable using instrumentation data for profile-guided optimization
  -fno-reroll-loops       Turn off loop reroller
  -fno-rtti               Disable generation of rtti information
  -fno-sanitize-blacklist Don't use blacklist file for sanitizers
  -fno-sanitize-cfi-cross-dso
                          Disable control flow integrity (CFI) checks for cross-DSO calls.
  -fno-sanitize-coverage=
                          Disable specified features of coverage instrumentation for Sanitizers
  -fno-sanitize-memory-track-origins
                          Disable origins tracking in MemorySanitizer
  -fno-sanitize-recover=
                          Disable recovery for specified sanitizers
  -fno-sanitize-stats     Disable sanitizer statistics gathering.
  -fno-sanitize-trap=
                          Disable trapping for specified sanitizers
  -fno-short-wchar        Force wchar_t to be an unsigned int
  -fno-show-column        Do not include column number on diagnostics
  -fno-show-source-location
                          Do not include source location information with diagnostics
  -fno-signed-char        Char is unsigned
  -fno-signed-zeros       Allow optimizations that ignore the sign of floating point zeros
  -fno-spell-checking     Disable spell-checking
  -fno-stack-protector    Disable the use of stack protectors
  -fno-standalone-debug   Limit debug information produced to reduce size of debug binary
  -fno-threadsafe-statics Do not emit code to make initialization of local statics thread safe
  -fno-trigraphs          Do not process trigraph sequences
  -fno-unroll-loops       Turn off loop unroller
  -fno-use-cxa-atexit     Don't use __cxa_atexit for calling destructors
  -fno-use-init-array     Don't use .init_array instead of .ctors
  -fobjc-arc-exceptions   Use EH-safe code when synthesizing retains and releases in -fobjc-arc
  -fobjc-arc              Synthesize retain and release calls for Objective-C pointers
  -fobjc-exceptions       Enable Objective-C exceptions
  -fobjc-gc-only          Use GC exclusively for Objective-C related memory management
  -fobjc-gc               Enable Objective-C garbage collection
  -fobjc-runtime=  Specify the target Objective-C runtime kind and version
  -fobjc-weak             Enable ARC-style weak references in Objective-C
  -fopenmp-targets=
                          Specify comma-separated list of triples OpenMP offloading targets to be supported
  -foptimization-record-file=
                          Specify the file name of any generated YAML optimization record
  -fpack-struct=   Specify the default maximum struct packing alignment
  -fpascal-strings        Recognize and construct Pascal-style string literals
  -fpcc-struct-return     Override the default ABI to return all structs on the stack
  -fplugin=      Load the named plugin (dynamic shared object)
  -fprebuilt-module-path=<directory>
                          Specify the prebuilt module path
  -fprofile-generate=
                          Generate instrumented code to collect execution counts into /default.profraw (overridden by LLVM_PROFILE_FILE env var)
  -fprofile-generate      Generate instrumented code to collect execution counts into default.profraw (overridden by LLVM_PROFILE_FILE env var)
  -fprofile-instr-generate=
                          Generate instrumented code to collect execution counts into  (overridden by LLVM_PROFILE_FILE env var)
  -fprofile-instr-generate
                          Generate instrumented code to collect execution counts into default.profraw file (overriden by '=' form of option or LLVM_PROFILE_FILE env var)
  -fprofile-instr-use=
                          Use instrumentation data for profile-guided optimization
  -fprofile-sample-use=
                          Enable sample-based profile guided optimizations
  -fprofile-use=
                          Use instrumentation data for profile-guided optimization. If pathname is a directory, it reads from /default.profdata. Otherwise, it reads from file .
  -freciprocal-math       Allow division operations to be reassociated
  -freg-struct-return     Override the default ABI to return small structs in registers
  -freroll-loops          Turn on loop reroller
  -fsanitize-address-field-padding=
                          Level of field padding for AddressSanitizer
  -fsanitize-address-use-after-scope
                          Enable use-after-scope detection in AddressSanitizer
  -fsanitize-blacklist=
                          Path to blacklist file for sanitizers
  -fsanitize-cfi-cross-dso
                          Enable control flow integrity (CFI) checks for cross-DSO calls.
  -fsanitize-coverage=
                          Specify the type of coverage instrumentation for Sanitizers
  -fsanitize-memory-track-origins=
                          Enable origins tracking in MemorySanitizer
  -fsanitize-memory-track-origins
                          Enable origins tracking in MemorySanitizer
  -fsanitize-memory-use-after-dtor
                          Enable use-after-destroy detection in MemorySanitizer
  -fsanitize-recover=
                          Enable recovery for specified sanitizers
  -fsanitize-stats        Enable sanitizer statistics gathering.
  -fsanitize-trap= Enable trapping for specified sanitizers
  -fsanitize-undefined-strip-path-components=
                          Strip (or keep only, if negative) a given number of path components when emitting check metadata.
  -fsanitize=      Turn on runtime checks for various forms of undefined or suspicious behavior. See user manual for available checks
  -fsave-optimization-record
                          Generate a YAML optimization record file
  -fshort-enums           Allocate to an enum type only as many bytes as it needs for the declared range of possible values
  -fshort-wchar           Force wchar_t to be a short unsigned int
  -fshow-overloads=
                          Which overload candidates to show when overload resolution fails: best|all; defaults to all
  -fsized-deallocation    Enable C++14 sized global deallocation functions
  -fsjlj-exceptions       Use SjLj style exceptions
  -fslp-vectorize-aggressive
                          Enable the BB vectorization passes
  -fslp-vectorize         Enable the superword-level parallelism vectorization passes
  -fstack-protector-all   Force the usage of stack protectors for all functions
  -fstack-protector-strong
                          Use a strong heuristic to apply stack protectors to functions
  -fstack-protector       Enable stack protectors for functions potentially vulnerable to stack smashing
  -fstandalone-debug      Emit full debug info for all types used by the program
  -fstrict-enums          Enable optimizations based on the strict definition of an enum's value range
  -fstrict-vtable-pointers
                          Enable optimizations based on the strict rules for overwriting polymorphic C++ objects
  -fthinlto-index= Perform ThinLTO importing using provided function summary index
  -ftrap-function= Issue call to specified function rather than a trap instruction
  -ftrapv-handler=
                          Specify the function to be called on overflow
  -ftrapv                 Trap on integer overflow
  -ftrigraphs             Process trigraph sequences
  -funique-section-names  Use unique names for text and data sections (ELF Only)
  -funroll-loops          Turn on loop unroller
  -fuse-init-array        Use .init_array instead of .ctors
  -fveclib=        Use the given vector functions library
  -fvectorize             Enable the loop vectorization passes
  -fvisibility-inlines-hidden
                          Give inline C++ member functions default visibility by default
  -fvisibility-ms-compat  Give global types 'default' visibility and global functions and variables 'hidden' visibility by default
  -fvisibility=    Set the default symbol visibility for all global declarations
  -fwhole-program-vtables Enables whole-program vtable optimization. Requires -flto
  -fwrapv                 Treat signed integer overflow as two's complement
  -fwritable-strings      Store string literals as writable data
  -fxray-instruction-threshold= 
                          Sets the minimum function size to instrument with XRay
  -fxray-instrument       Generate XRay instrumentation sleds on function entry and exit
  -fzvector               Enable System z vector language extension
  -F               Add directory to framework include search path
  --gcc-toolchain= Use the gcc toolchain at the given directory
  -gcodeview              Generate CodeView debug information
  -gdwarf-2               Generate source-level debug information with dwarf version 2
  -gdwarf-3               Generate source-level debug information with dwarf version 3
  -gdwarf-4               Generate source-level debug information with dwarf version 4
  -gdwarf-5               Generate source-level debug information with dwarf version 5
  -gline-tables-only      Emit debug line number tables only
  -gmodules               Generate debug info with external references to clang modules or precompiled headers
  -g                      Generate source-level debug information
  -help                   Display available options
  -H                      Show header includes and nesting depth
  -iapinotes-modules 
                          Add directory to the API notes search path referenced by module name
  -idirafter       Add directory to AFTER include search path
  -iframework      Add directory to SYSTEM framework search path
  -imacros          Include macros from file before parsing
  -include-pch      Include precompiled header file
  -include          Include file before parsing
  -index-header-map       Make the next included directory (-I or -F) an indexer header map
  -index-ignore-system-symbols
                          Ignore symbols from system headers
  -index-record-codegen-name
                          Record the codegen name for symbols
  -index-store-path 
                          Enable indexing with the specified data store path
  -iprefix           Set the -iwithprefix/-iwithprefixbefore prefix
  -iquote      Add directory to QUOTE include search path
  -isysroot          Set the system root directory (usually /)
  -isystem-after 
                          Add directory to end of the SYSTEM include search path
  -isystem     Add directory to SYSTEM include search path
  -ivfsoverlay     Overlay the virtual filesystem described by file over the real file system
  -iwithprefixbefore 
                          Set directory to include search path with prefix
  -iwithprefix       Set directory to SYSTEM include search path with prefix
  -iwithsysroot 
                          Add directory to SYSTEM include search path, absolute paths are relative to -isysroot
  -I               Add directory to include search path
  -mabicalls              Enable SVR4-style position-independent code (Mips only)
  -malign-double          Align doubles to two words in structs (x86 only)
  -mbackchain             Link stack frames through backchain on System Z
  -mcrc                   Allow use of CRC instructions (ARM only)
  -MD                     Write a depfile containing user and system headers
  -meabi           Set EABI type, e.g. 4, 5 or gnu (default depends on triple)
  -mfix-cortex-a53-835769 Workaround Cortex-A53 erratum 835769 (AArch64 only)
  -mfp32                  Use 32-bit floating point registers (MIPS only)
  -mfp64                  Use 64-bit floating point registers (MIPS only)
  -MF               Write depfile output from -MMD, -MD, -MM, or -M to 
  -mgeneral-regs-only     Generate code which only uses the general purpose registers (AArch64 only)
  -mglobal-merge          Enable merging of globals
  -MG                     Add missing headers to depfile
  -mhvx-double            Enable Hexagon Double Vector eXtensions
  -mhvx                   Enable Hexagon Vector eXtensions
  -miamcu                 Use Intel MCU ABI
  --migrate               Run the migrator
  -mincremental-linker-compatible
                          (integrated-as) Emit an object file which can be used with an incremental linker
  -mios-version-min=
                          Set iOS deployment target
  -mllvm           Additional arguments to forward to LLVM's option processing
  -mlong-calls            Generate an indirect jump to enable jumps further than 64M
  -mmacosx-version-min=
                          Set Mac OS X deployment target
  -MMD                    Write a depfile containing user headers
  -mms-bitfields          Set the default structure layout to be compatible with the Microsoft compiler standard
  -mmsa                   Enable MSA ASE (MIPS only)
  -MM                     Like -MMD, but also implies -E and writes to stdout by default
  -mno-abicalls           Disable SVR4-style position-independent code (Mips only)
  -mno-fix-cortex-a53-835769
                          Don't workaround Cortex-A53 erratum 835769 (AArch64 only)
  -mno-global-merge       Disable merging of globals
  -mno-hvx-double         Disable Hexagon Double Vector eXtensions
  -mno-hvx                Disable Hexagon Vector eXtensions
  -mno-implicit-float     Don't generate implicit floating point instructions
  -mno-incremental-linker-compatible
                          (integrated-as) Emit an object file which cannot be used with an incremental linker
  -mno-long-calls         Restore the default behaviour of not generating long calls
  -mno-movt               Disallow use of movt/movw pairs (ARM only)
  -mno-ms-bitfields       Do not set the default structure layout to be compatible with the Microsoft compiler standard
  -mno-msa                Disable MSA ASE (MIPS only)
  -mno-restrict-it        Allow generation of deprecated IT blocks for ARMv8. It is off by default for ARMv8 Thumb mode
  -mno-unaligned-access   Force all memory accesses to be aligned (AArch32/AArch64 only)
  -mnocrc                 Disallow use of CRC instructions (ARM only)
  -module-dependency-dir <value>
                          Directory to dump module dependencies to
  -momit-leaf-frame-pointer
                          Omit frame pointer setup for leaf functions
  -MP                     Create phony target for each dependency (other than main file)
  -mqdsp6-compat          Enable hexagon-qdsp6 backward compatibility
  -MQ              Specify name of main file output to quote in depfile
  -mrelax-all             (integrated-as) Relax all machine instructions
  -mrestrict-it           Disallow generation of deprecated IT blocks for ARMv8. It is on by default for ARMv8 Thumb mode.
  -mrtd                   Make StdCall calling convention the default
  -msoft-float            Use software floating point
  -mstack-alignment=
                          Set the stack alignment
  -mstack-probe-size=
                          Set the stack probe size
  -mstackrealign          Force realign the stack at entry to every function
  -mthread-model   The thread model to use, e.g. posix, single (posix by default)
  -MT              Specify name of main file output in depfile
  -munaligned-access      Allow memory accesses to be unaligned (AArch32/AArch64 only)
  -MV                     Use NMake/Jom format for the depfile
  -M                      Like -MD, but also implies -E and writes to stdout by default
  --no-cuda-version-check Don't error out if the detected version of the CUDA install is too low for the requested CUDA gpu architecture.
  --no-system-header-prefix=
                          Treat all #include paths starting with  as not including a system header.
  -nobuiltininc           Disable builtin #include directories
  -nostdinc++             Disable standard #include directories for the C++ standard library
  -ObjC++                 Treat source input files as Objective-C++ inputs
  -objcmt-atomic-property Make migration to 'atomic' properties
  -objcmt-migrate-all     Enable migration to modern ObjC
  -objcmt-migrate-annotation
                          Enable migration to property and method annotations
  -objcmt-migrate-designated-init
                          Enable migration to infer NS_DESIGNATED_INITIALIZER for initializer methods
  -objcmt-migrate-instancetype
                          Enable migration to infer instancetype for method result type
  -objcmt-migrate-literals
                          Enable migration to modern ObjC literals
  -objcmt-migrate-ns-macros
                          Enable migration to NS_ENUM/NS_OPTIONS macros
  -objcmt-migrate-property-dot-syntax
                          Enable migration of setter/getter messages to property-dot syntax
  -objcmt-migrate-property
                          Enable migration to modern ObjC property
  -objcmt-migrate-protocol-conformance
                          Enable migration to add protocol conformance on classes
  -objcmt-migrate-readonly-property
                          Enable migration to modern ObjC readonly property
  -objcmt-migrate-readwrite-property
                          Enable migration to modern ObjC readwrite property
  -objcmt-migrate-subscripting
                          Enable migration to modern ObjC subscripting
  -objcmt-ns-nonatomic-iosonly
                          Enable migration to use NS_NONATOMIC_IOSONLY macro for setting property's 'atomic' attribute
  -objcmt-returns-innerpointer-property
                          Enable migration to annotate property with NS_RETURNS_INNER_POINTER
  -objcmt-whitelist-dir-path=
                          Only modify files with a filename contained in the provided directory path
  -ObjC                   Treat source input files as Objective-C inputs
  -o                Write output to 
  -pg                     Enable mcount instrumentation
  -pipe                   Use pipes between commands, when possible
  -print-file-name= Print the full library path of 
  -print-ivar-layout      Enable Objective-C Ivar layout bitmap print trace
  -print-libgcc-file-name Print the library path for "libgcc.a"
  -print-prog-name= Print the full program path of 
  -print-search-dirs      Print the paths used for finding libraries and programs
  -pthread                Support POSIX threads in generated code
  -P                      Disable linemarker output in -E mode
  -Qunused-arguments      Don't emit warning for unused driver arguments
  -relocatable-pch        Whether to build a relocatable precompiled header
  -rewrite-legacy-objc    Rewrite Legacy Objective-C source to C++
  -rewrite-objc           Rewrite Objective-C source to C++
  -Rpass-analysis= Report transformation analysis from optimization passes whose name matches the given POSIX regular expression
  -Rpass-missed=   Report missed transformations by optimization passes whose name matches the given POSIX regular expression
  -Rpass=          Report transformations performed by optimization passes whose name matches the given POSIX regular expression
  -R              Enable the specified remark
  -save-stats=     Save llvm statistics.
  -save-stats             Save llvm statistics.
  -save-temps=     Save intermediate compilation results.
  -save-temps             Save intermediate compilation results
  -serialize-diagnostics 
                          Serialize compiler diagnostics to a file
  -std=            Language standard to compile for
  -stdlib=         C++ standard library to use
  --system-header-prefix=
                          Treat all #include paths starting with  as including a system header.
  -S                      Only run preprocess and compilation steps
  --target=        Generate code for the given target
  -time                   Time individual commands
  -traditional-cpp        Enable some traditional CPP emulation
  -trigraphs              Process trigraph sequences
  -undef                  undef all system defines
  --verify-debug-info     Verify the binary representation of debug output
  -verify-pch             Load and verify that a pre-compiled header file is not stale
  -v                      Show commands to run and use verbose output
  -Wa,               Pass the comma separated arguments in  to the assembler
  -Wl,               Pass the comma separated arguments in  to the linker
  -working-directory 
                          Resolve file paths relative to the specified directory
  -Wp,               Pass the comma separated arguments in  to the preprocessor
  -W             Enable the specified warning
  -w                      Suppress all warnings
  -Xanalyzer         Pass  to the static analyzer
  -Xassembler        Pass  to the assembler
  -Xclang            Pass  to the clang compiler
  -Xcuda-fatbinary   Pass  to fatbinary invocation
  -Xcuda-ptxas       Pass  to the ptxas assembler
  -Xlinker           Pass  to the linker
  -Xpreprocessor     Pass  to the preprocessor
  -x            Treat subsequent input files as having type 
  -z                 Pass -z  to the linker

生成中间代码

2.c代码

#include 

int main(){
        int i=1024;
void (^blk)(void) = ^{
                printf("i=%d", i); 
        };  
        blk();
        return 0;
}

生成中间代码

clang  -emit-llvm 2.c -S -o 2.o

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