Modify Your makefile

Intel® C++ Compiler Classic Developer Guide and Reference

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ID 767249

Date 3/31/2023

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Public

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Modify 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 Classic. You may also want to review the options specified by CFLAGS. For example, a 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

Modified makefile for the Intel® C++ Compiler Classic

In this example, the name of the compiler is changed to use icc

# Use Intel C/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 Classic (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 Classic 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 Classic. The following sample makefile is modified for using the Intel® C++ Compiler Classic and GCC together:

# Use Intel C/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

Use 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 to link as shown in the example:

# Use Intel C/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

Parent topic: Port from GCC* to the Intel® C++ Compiler Classic

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Intel® C++ Compiler Classic Developer Guide and Reference

Modify Your makefile

Modified makefile for the Intel® C++ Compiler Classic