Modify makefiles for GCC Applications

Intel® oneAPI DPC++/C++ Compiler

Developer Guide and Reference

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ID 767253

Date 3/31/2025

Version

Public

Modify makefiles for GCC Applications

If you use makefiles to build your GCC* application, you need to change the value for the GCC compiler variable to use the Intel® oneAPI DPC++/C++ Compiler. 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 makefiles for the Intel® oneAPI DPC++/C++ Compiler

In the following example, the name of the compiler is changed to use icpx:


# Use Intel oneAPI DPC++/C++ Compiler
  CC = icpx

# 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® oneAPI DPC++/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® oneAPI DPC++/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® oneAPI DPC++/C++ Compiler. The following example is modified to use the Intel® oneAPI DPC++/C++ Compiler and GCC together:


# Use Intel oneAPI DPC++/C++ Compiler
  CC = icpx
# Use gcc for files that cannot be compiled by icpx
  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

An example output of make using a modified makefile:


icpx -c -std=c99 area_main.c
gcc -c -O2 -fno-asm -std=c99 area_functions.c
icpx 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 LLVM-provided tools. To use them in your makefile, simply replace references to ld with lld-link and references to ar with llvm-ar, or use the Intel® oneAPI DPC++/C++ Compiler to link as shown in the following example:


# Use Intel oneAPI DPC++/C++ Compiler 
  CC =icpx
# 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® oneAPI DPC++/C++ Compiler

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Developer Guide and Reference

Modify makefiles for GCC Applications

Modified makefiles for the Intel® oneAPI DPC++/C++ Compiler

Use IPO in makefiles