buildOptionsInc.adoc

Compiler Options

The compiler options are categorized as pre-processor options, options for math intrinsics, options that control optimization and miscellaneous options. This specification defines a standard set of options that must be supported by the OpenCL C compiler when building program executables online or offline. These may be extended by a set of vendor- or platform specific options.

Preprocessor Options

These options control the OpenCL C preprocessor which is run on each program source before actual compilation.

-D options are processed in the order they are given in the options argument to clBuildProgram or clCompileProgram.

-D name

Predefine name as a macro, with definition 1.

-D name=definition

The contents of definition are tokenized and processed as if they appeared during translation phase three in a '#define' directive. In particular, the definition will be truncated by embedded newline characters.

-I dir

Add the directory dir to the list of directories to be searched for header files.

Math Intrinsics Options

These options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness.

-cl-single-precision-constant

Treat double precision floating-point constant as single precision constant.

-cl-denorms-are-zero

This option controls how single precision and double precision denormalized numbers are handled. If specified as a build option, the single precision denormalized numbers may be flushed to zero; double precision denormalized numbers may also be flushed to zero if the optional extension for double precsion is supported. This is intended to be a performance hint and the OpenCL compiler can choose not to flush denorms to zero if the device supports single precision (or double precision) denormalized numbers.

This option is ignored for single precision numbers if the device does not support single precision denormalized numbers i.e. CL_FP_DENORM bit is not set in CL_DEVICE_SINGLE_FP_CONFIG.

This option is ignored for double precision numbers if the device does not support double precision or if it does support double precison but not double precision denormalized numbers i.e. CL_FP_DENORM bit is not set in CL_DEVICE_DOUBLE_FP_CONFIG.

This flag only applies for scalar and vector single precision floating-point variables and computations on these floating-point variables inside a program. It does not apply to reading from or writing to image objects.

-cl-fp32-correctly-rounded-divide-sqrt

The -cl-fp32-correctly-rounded-divide-sqrt build option to clBuildProgram or clCompileProgram allows an application to specify that single precision floating-point divide (x/y and 1/x) and sqrt used in the program source are correctly rounded. If this build option is not specified, the minimum numerical accuracy of single precision floating-point divide and sqrt are as defined in section 7.4 of the OpenCL specification.

This build option can only be specified if the CL_FP_CORRECTLY_ROUNDED_DIVIDE_SQRT is set in CL_DEVICE_SINGLE_FP_CONFIG (as defined in in the table of allowed values for param_name for clGetDeviceInfo) for devices that the program is being build. clBuildProgram or clCompileProgram will fail to compile the program for a device if the -cl-fp32-correctly-rounded-divide-sqrt option is specified and CL_FP_CORRECTLY_ROUNDED_DIVIDE_SQRT is not set for the device.

Optimization Options

These options control various sorts of optimizations. Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program.

-cl-opt-disable

This option disables all optimizations. The default is optimizations are enabled.

The following options control compiler behavior regarding floating-point arithmetic. These options trade off between performance and correctness and must be specifically enabled. These options are not turned on by default since it can result in incorrect output for programs which depend on an exact implementation of IEEE 754 rules/specifications for math functions.

-cl-mad-enable

Allow a * b + c to be replaced by a mad. The mad computes a * b + c with reduced accuracy. For example, some OpenCL devices implement mad as truncate the result of a * b before adding it to c.

-cl-no-signed-zeros

Allow optimizations for floating-point arithmetic that ignore the signedness of zero. IEEE 754 arithmetic specifies the distinct behavior of +0.0 and -0.0 values, which then prohibits simplification of expressions such as x+0.0 or 0.0*x (even with -clfinite-math only). This option implies that the sign of a zero result isn’t significant.

-cl-unsafe-math-optimizations

Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid, (b) may violate IEEE 754 standard and (c) may violate the OpenCL numerical compliance requirements as defined in section 7.4 for single precision and double precision floating-point, and edge case behavior in section 7.5. This option includes the -cl-no-signed-zeros and -cl-mad-enable options.

-cl-finite-math-only

Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or ±∞. This option may violate the OpenCL numerical compliance requirements defined in section 7.4 for single precision and double precision floating point, and edge case behavior in section 7.5.

-cl-fast-relaxed-math

Sets the optimization options -cl-finite-math-only and -cl-unsafe-math-optimizations. This allows optimizations for floating-point arithmetic that may violate the IEEE 754 standard and the OpenCL numerical compliance requirements defined in the specification in section 7.4 for single-precision and double precision floating-point, and edge case behavior in section 7.5. This option also relaxes the precision of commonly used math functions (refer to table 7.2 defined in section 7.4). This option causes the preprocessor macro FAST_RELAXED_MATH to be defined in the OpenCL program.

-cl-uniform-work-group-size

This requires that the global work-size be a multiple of the work-group size specified to clEnqueueNDRangeKernel. Allow optimizations that are made possible by this restriction.

Options to Request or Suppress Warnings

Warnings are diagnostic messages that report constructions which are not inherently erroneous but which are risky or suggest there may have been an error. The following language independent options do not enable specific warnings but control the kinds of diagnostics produced by the OpenCL compiler.

-w

Inhibit all warning messages.

-Werror

Make all warnings into errors.

Options Controlling the OpenCL C Version

The following option controls the version of OpenCL C that the compiler accepts.

-cl-std=

Determine the OpenCL C language version to use. A value for this option must be provided. Valid values are:

CL1.1 - Support all OpenCL C programs that use the OpenCL C language features defined in section 6 of the OpenCL 1.1 specification.

CL1.2 - Support all OpenCL C programs that use the OpenCL C language features defined in section 6 of the OpenCL 1.2 specification.

CL2.0 - Support all OpenCL C programs that use the OpenCL C language features defined in section 6 of the OpenCL 2.0 specification.

Calls to clBuildProgram or clCompileProgram with the -cl-std=CL1.1 option will fail to compile the program for any devices with CL_DEVICE_OPENCL_C_VERSION = OpenCL C 1.0.

Calls to clBuildProgram or clCompileProgram with the -cl-std=CL1.2 option will fail to compile the program for any devices with CL_DEVICE_OPENCL_C_VERSION = OpenCL C 1.0 or OpenCL C 1.1.

Calls to clBuildProgram or clCompileProgram with the -cl-std=CL2.0 option will fail to compile the program for any devices with CL_DEVICE_OPENCL_C_VERSION = OpenCL C 1.0, OpenCL C 1.1, or OpenCL C 1.2.

If the –cl-std build option is not specified, the highest OpenCL C 1.x language version supported by each device is used when compiling the program for each device. Applications are required to specify the –cl-std=CL2.0 option if they want to compile or build their programs with OpenCL C 2.0.

Options enabled by the cl_khr_spir extension

-x spir

Indicates that the binary is in SPIR format.

-spir-std

Specifies the version of the SPIR specification that describes the format and meaning of the binary. For example, if the binary is as described in SPIR version 1.2, then -spir-std=1.2 must be specified. Failing to specify these compile options may result in implementation defined behavior.

Options for Querying Kernel Argument Information

-cl-kernel-arg-info

This option allows the compiler to store information about the arguments of a kernel(s) in the program executable. The argument information stored includes the argument name, its type, the address and access qualifiers used. Refer to description of clGetKernelArgInfo on how to query this information.

Options for debugging your program

-g

This option can currently be used to generate additional errors for the built-in functions that allow you to enqueue commands on a device (refer to section 6.13.17).

Linker Options

This specification defines a standard set of linker options that must be supported by the OpenCL C compiler when linking compiled programs online or offline. These linker options are categorized as library linking options and program linking options. These may be extended by a set of vendor- or platform-specific options.

Library Linking Options

The following options can be specified when creating a library of compiled binaries.

-create-library

Create a library of compiled binaries specified in input_programs argument to clLinkProgram.

-enable-link-options

Allows the linker to modify the library behavior based on one or more link options (described in Program Linking Options, below) when this library is linked with a program executable. This option must be specified with the -create-library option.

Program Linking Options

The following options can be specified when linking a program executable.

• -cl-denorms-are-zero

• -cl-no-signed-zeroes

• -cl-unsafe-math-optimizations

• -cl-finite-math-only

• -cl-fast-relaxed-mat

The linker may apply these options to all compiled program objects specified to clLinkProgram. The linker may apply these options only to libraries which were created with the -enable-link-option.

Separate Compilation and Linking of Programs

OpenCL programs are compiled and linked to support the following:

• Separate compilation and link stages. Program sources can be compiled to generate a compiled binary object and linked in a separate stage with other compiled program objects to the program exectuable.

• Embedded headers. In OpenCL 1.0 and 1.1, the -I build option could be used to specify the list of directories to be searched for headers files that are included by a program source(s). OpenCL 1.2 extends this by allowing the header sources to come from program objects instead of just header files.

• Libraries. The linker can be used to link compiled objects and libraries into a program executable or to create a library of compiled binaries.