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clang及参数和生成中间代码

汇编

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 compilerUSAGE: 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). --analyzeRun 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-zeroOpenCL only. Allow denormals to be flushed to zero. -cl-fast-relaxed-mathOpenCL only. Sets -cl-finite-math-only and -cl-unsafe-math-optimizations, and defines __FAST_RELAXED_MATH__. -cl-finite-math-onlyOpenCL 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-infoOpenCL only. Generate kernel argument metadata. -cl-mad-enableOpenCL only. Allow use of less precise MAD computations in the generated binary. -cl-no-signed-zerosOpenCL only. Allow use of less precise no signed zeros computations in the generated binary. -cl-opt-disableOpenCL 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-aliasingOpenCL 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-onlyCompile CUDA code for device only --cuda-gpu-arch= CUDA GPU architecture (e.g. sm_35).May be specified more than once. --cuda-host-onlyCompile 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 -cOnly run preprocess, compile, and assemble steps -dDPrint 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 -dMPrint macro definitions in -E mode instead of normal output -emit-astEmit Clang AST files for source inputs -emit-llvmUse the LLVM representation for assembler and object files -EOnly run the preprocessor -faltivecEnable AltiVec vector initializer syntax -fansi-escape-codesUse ANSI escape codes for diagnostics -fapinotes-cache-path= Specify the API notes cache path -fapinotes-modulesEnable module-based external API notes support -fapinotes-swift-version= Specify the Swift version to use when filtering API notes -fapinotesEnable external API notes support -fapple-kextUse Apple's kernel extensions ABI -fapple-pragma-packEnable Apple gcc-compatible #pragma pack handling -fapplication-extension Restrict code to those available for App Extensions -fblocksEnable the 'blocks' language feature -fborland-extensionsAccept 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=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 -mabicallsEnable SVR4-style position-independent code (Mips only) -malign-doubleAlign doubles to two words in structs (x86 only) -mbackchainLink stack frames through backchain on System Z -mcrcAllow use of CRC instructions (ARM only) -MDWrite 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) -mfp32Use 32-bit floating point registers (MIPS only) -mfp64Use 64-bit floating point registers (MIPS only) -MF Write depfile output from -MMD, -MD, -MM, or -M to -mgeneral-regs-onlyGenerate code which only uses the general purpose registers (AArch64 only) -mglobal-mergeEnable merging of globals -MGAdd missing headers to depfile -mhvx-doubleEnable Hexagon Double Vector eXtensions -mhvxEnable Hexagon Vector eXtensions -miamcuUse Intel MCU ABI --migrateRun 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-callsGenerate an indirect jump to enable jumps further than 64M -mmacosx-version-min= Set Mac OS X deployment target -MMDWrite a depfile containing user headers -mms-bitfieldsSet the default structure layout to be compatible with the Microsoft compiler standard -mmsaEnable MSA ASE (MIPS only) -MMLike -MMD, but also implies -E and writes to stdout by default -mno-abicallsDisable SVR4-style position-independent code (Mips only) -mno-fix-cortex-a53-835769 Don't workaround Cortex-A53 erratum 835769 (AArch64 only) -mno-global-mergeDisable merging of globals -mno-hvx-doubleDisable Hexagon Double Vector eXtensions -mno-hvxDisable Hexagon Vector eXtensions -mno-implicit-floatDon'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-callsRestore the default behaviour of not generating long calls -mno-movtDisallow use of movt/movw pairs (ARM only) -mno-ms-bitfieldsDo not set the default structure layout to be compatible with the Microsoft compiler standard -mno-msaDisable MSA ASE (MIPS only) -mno-restrict-itAllow generation of deprecated IT blocks for ARMv8. It is off by default for ARMv8 Thumb mode -mno-unaligned-accessForce all memory accesses to be aligned (AArch32/AArch64 only) -mnocrcDisallow use of CRC instructions (ARM only) -module-dependency-dir Directory to dump module dependencies to -momit-leaf-frame-pointer Omit frame pointer setup for leaf functions -MPCreate phony target for each dependency (other than main file) -mqdsp6-compatEnable hexagon-qdsp6 backward compatibility -MQ Specify name of main file output to quote in depfile -mrelax-all(integrated-as) Relax all machine instructions -mrestrict-itDisallow generation of deprecated IT blocks for ARMv8. It is on by default for ARMv8 Thumb mode. -mrtdMake StdCall calling convention the default -msoft-floatUse software floating point -mstack-alignment= Set the stack alignment -mstack-probe-size= Set the stack probe size -mstackrealignForce 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-accessAllow memory accesses to be unaligned (AArch32/AArch64 only) -MVUse NMake/Jom format for the depfile -MLike -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. -nobuiltinincDisable 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-allEnable 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 -ObjCTreat source input files as Objective-C inputs -o Write output to -pgEnable mcount instrumentation -pipeUse pipes between commands, when possible -print-file-name= Print the full library path of -print-ivar-layoutEnable 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-dirsPrint the paths used for finding libraries and programs -pthreadSupport POSIX threads in generated code -PDisable linemarker output in -E mode -Qunused-argumentsDon't emit warning for unused driver arguments -relocatable-pchWhether to build a relocatable precompiled header -rewrite-legacy-objcRewrite Legacy Objective-C source to C++ -rewrite-objcRewrite 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 -REnable the specified remark -save-stats=Save llvm statistics. -save-statsSave llvm statistics. -save-temps=Save intermediate compilation results. -save-tempsSave 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. -SOnly run preprocess and compilation steps --target=Generate code for the given target -timeTime individual commands -traditional-cppEnable some traditional CPP emulation -trigraphsProcess trigraph sequences -undefundef all system defines --verify-debug-infoVerify the binary representation of debug output -verify-pchLoad and verify that a pre-compiled header file is not stale -vShow commands to run and use verbose output -Wa,Pass the comma separated arguments into the assembler -Wl,Pass the comma separated arguments into the linker -working-directory Resolve file paths relative to the specified directory -Wp,Pass the comma separated arguments into the preprocessor -WEnable the specified warning -wSuppress all warnings -XanalyzerPassto the static analyzer -XassemblerPassto the assembler -XclangPassto the clang compiler -Xcuda-fatbinaryPassto fatbinary invocation -Xcuda-ptxasPassto the ptxas assembler -XlinkerPassto the linker -XpreprocessorPassto the preprocessor -x Treat subsequent input files as having type -zPass -zto 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; }

【clang及参数和生成中间代码】生成中间代码
clang-emit-llvm 2.c -S -o 2.o

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