#pragma GCC diagnostic ignored "-Wunused-parameter"和#pragma GCC diagnostic ignored "-Wdeprecated-declarations"极其有用
Suppressing Warnings in GCC and Clang (nelkinda.com)
GCC Command Line Options 下面列出一些有趣的：
--help={target|optimizers|warnings|params|[^]{joined|separate|undocumented}}[,...] Display specific types of command line options
-dumpspecs Display all of the built in spec strings
-print-search-dirs Display the directories in the compiler's search path
-print-sysroot Display the target libraries directory
-pipe Use pipes rather than intermediate files
-time Time the execution of each subprocess
--sysroot=<directory> Use <directory> as the root directory for headers and libraries
-B <directory> Add <directory> to the compiler's search paths
-v Display the programs invoked by the compiler
-E Preprocess only; do not compile, assemble or link
-S Compile only; do not assemble or link
-m128bit-long-double sizeof(long double) is 16
-m96bit-long-double sizeof(long double) is 12
-m32 Generate 32bit i386 code
-m3dnow Support 3DNow! built-in functions
-m3dnowa Support Athlon 3Dnow! built-in functions
-m64 Generate 64bit x86-64 code
-mabm Support code generation of Advanced Bit Manipulation (ABM) instructions.
-mavx Support MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2 and AVX built-in functions and code generation
-mwin32 Set Windows defines
-mwindows Create GUI application
-fPIC Generate position-independent code if possible (large mode)
-fPIE Generate position-independent code for executables if possible (large mode)
-pie Create a position independent executable
-shared Create a shared library
-g Generate debug information in default format
-ggdb Generate debug information in default extended format
-p Enable function profiling
-O<number> Set optimization level to <number>
-Os Optimize for space rather than speed
-Ofast Disregard strict standards compliance. -Ofast enables all -O3 optimizations.
Optimize Options (Using the GNU Compiler Collection (GCC)) 没有-O4，最高就是3:
