增加优化标志时,如何更改二进制文件？

我已经编制了不同的优化参数相同的程序:-O0,-O1,-O2,和-O3.我用过gcc和icc.您可以在下面看到make文件的一个片段:

build-gcc-O3: CXX = g++
build-gcc-O3: BIN_POST_NAME = -gcc-O3
build-gcc-O3: OPT_FLAGS = -O3
build-gcc-O3: fluidsGL

build-icc-O0: CXX = $(INTEL_ICPC)
build-icc-O0: BIN_POST_NAME = -icc-O0
build-icc-O0: OPT_FLAGS = -O0
build-icc-O0: fluidsGL

fluidsGL: fluidsGL.o fluidsGL_cpu.o bilinear_interpolation.o defines.o
   $(CXX) $(CXXFLAGS) $(BINARY_DIR)/defines.o $(BINARY_DIR)/bilinear_interpolation.o $(BINARY_DIR)/fluidsGL_cpu.o $(BINARY_DIR)/fluidsGL.o -o $(BINARY_DIR)/$@$(BIN_POST_NAME)$(DBG_NAME_APPEND) $(OPT_FLAGS) -lGL -lGLU -lGLEW -lglut -lfftw3f

运行make后,输出看起来很好.例如,这是icc的make结果命令-O3:

"/opt/intel/compilers_and_libraries/linux/bin/intel64/icpc" -Wall bin/defines.o bin/bilinear_interpolation.o bin/fluidsGL_cpu.o bin/fluidsGL.o -o bin/fluidsGL-icc-O3 -O3 -lGL -lGLU -lGLEW -lglut -lfftw3f

编译后,fluidGL-gcc-O0和fluidsGL-gcc-O3(以及fluidGL-icc-O0 vs fluidsGL-icc-O3)二进制文件需要相同的磁盘空间,这对我来说似乎很奇怪:

$ ls -la bin/ 
total 728
drwxrwxr-x 3 jesus jesus  4096 ene 18 09:56 .
drwxrwxr-x 7 jesus jesus  4096 ene 18 09:31 ..
-rw-rw-r-- 1 jesus jesus  4200 ene 18 09:56 bilinear_interpolation.o
-rw-rw-r-- 1 jesus jesus  5608 ene 18 09:56 defines.o
-rw-rw-r-- 1 jesus jesus 14952 ene 18 09:56 fluidsGL_cpu.o
-rwxrwxr-x 1 jesus jesus 30780 ene 18 09:56 fluidsGL-gcc-O0
-rwxrwxr-x 1 jesus jesus 43940 ene 18 09:56 fluidsGL-gcc-O0-dbg
-rwxrwxr-x 1 jesus jesus 44272 ene 18 09:56 fluidsGL-gcc-O0-dbg-gprof
-rwxrwxr-x 1 jesus jesus 30780 ene 18 09:56 fluidsGL-gcc-O1
-rwxrwxr-x 1 jesus jesus 30780 ene 18 09:56 fluidsGL-gcc-O2
-rwxrwxr-x 1 jesus jesus 30780 ene 18 09:56 fluidsGL-gcc-O3
-rwxrwxr-x 1 jesus jesus 71151 ene 18 09:56 fluidsGL-icc-O0
-rwxrwxr-x 1 jesus jesus 71151 ene 18 09:56 fluidsGL-icc-O1
-rwxrwxr-x 1 jesus jesus 71151 ene 18 09:56 fluidsGL-icc-O2
-rwxrwxr-x 1 jesus jesus 71151 ene 18 09:56 fluidsGL-icc-O3
-rw-rw-r-- 1 jesus jesus 34664 ene 18 09:56 fluidsGL.o

但即使使用diff来比较文件也没有显示输出,这意味着二进制文件是完全相同的二进制文件:

$ diff bin/fluidsGL-gcc-O0 bin/fluidsGL-gcc-O3
$ diff bin/fluidsGL-icc-O0 bin/fluidsGL-icc-O3
$

这是编译器的正常行为还是我犯了建筑错误？

该-Ox标志(这里x是优化级)是编译器优化,但你没有真正重新编译.您只是重新链接已编译的object(.o)文件.

确保将-Ox标志添加到目标文件的编译命令,并执行完全干净的重建.