Modifying Your makefile

If you use makefiles to build your gcc* application, you need to change the value for the GCC compiler variable to use the Intel® C++ Compiler. You may also want to review the options specified by CFLAGS. For example:

Sample gcc* makefile

# Use gcc compiler 
  CC = gcc 

# Compile-time flags 
  CFLAGS = -O2 -std=c99 
all: area_app 

area_app: area_main.o area_functions.o
    $(CC) area_main.o area_functions.o -o area 

area_main.o: area_main.c
    $(CC) -c $(CFLAGS) area_main.c 

area_functions.o: area_functions.c
    $(CC) -c -fno-asm $(CFLAGS) area_functions.c 

clean: rm -rf *o area

Sample makefile modified for the Intel® C/C++ Compiler

# Use Intel C Compiler 
  CC = icc 

# Compile-time flags 
  CFLAGS = -std=c99 
all: area_app 

area_app: area_main.o area_functions.o
    $(CC) area_main.o area_functions.o -o area 

area_main.o: area_main.c
    $(CC) -c $(CFLAGS) area_main.c 

area_functions.o: area_functions.c
    $(CC) -c -fno-asm $(CFLAGS) area_functions.c 

clean: rm -rf *o area

If your gcc* code includes features that are not supported with the Intel® C++ Compiler (compiler options, language extensions, macros, pragmas, and so on), you can compile those sources separately with gcc* if necessary.

In the above makefile, area_functions.c is an example of a source file that includes features unique to gcc*. Because the Intel® C++ Compiler uses the O2 option by default and gcc* uses option O0 as the default, we instruct gcc* to compile at option O2. We also include the -fno-asm switch from the original makefile because this switch is not supported with the Intel® C++ Compiler.

Sample makefile modified for using the Intel® C/C++ Compiler and gcc together
# Use Intel C Compiler 
  CC = icc 
# Use gcc for files that cannot be compiled by icc
  GCC = gcc
# Compile-time flags 
  CFLAGS = -std=c99 
all: area_app 

area_app: area_main.o area_functions.o
    $(CC) area_main.o area_functions.o -o area 

area_main.o: area_main.c
    $(CC) -c $(CFLAGS) area_main.c 

area_functions.o: area_functions.c
    $(GCC) -c -O2 -fno-asm $(CFLAGS) area_functions.c 

clean: rm -rf *o area

Output of make using a modified makefile

icc -c -std=c99 area_main.c
gcc -c -O2 -fno-asm -std=c99 area_functions.c
icc area_main.o area_functions.o -o area

Using IPO in Makefiles

By default, IPO generates "dummy" object files containing Interprocedural information used by the compiler. To link or create static libraries with these object files requires special Intel®-provided tools. To use them in your makefile, simply replace references to "ld" with "xild" and references to "ar" with "xiar", or use icc or icpc to link as shown below.

Sample makefile modified for the Intel® C/C++ Compiler with IPO
# Use Intel C Compiler 
  CC = icc 

# Compile-time flags 
  CFLAGS = -std=c99 -ipo
all: area_app 

area_app: area_main.o area_functions.o
    $(CC) area_main.o area_functions.o -o area 

area_main.o: area_main.c
    $(CC) -c $(CFLAGS) area_main.c 

area_functions.o: area_functions.c
    $(CC) -c $(CFLAGS) area_functions.c 

clean: rm -rf *o area

Para obtener información más completa sobre las optimizaciones del compilador, consulte nuestro Aviso de optimización.