User Guide

© 2021 IBM Corporation
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IBM
®
Power
®
Power10 Quick-start Guide – GNU Compiler Collection (GCC)
Availability
• The GCC compilers are available on all Enterprise Linux distributions and on
AIX.
• The installed GCC version is 8.4 on RHEL 8 and 7.4 on SLES 15. RHEL 9 is
expected to ship GCC 11.2.
• There are several ways to obtain a sufficiently recent version of GCC when
the default compilers for the distribution are too old to support Power10.
• Red Hat supports the GCC Toolset
[1] for this purpose.
• SUSE provides the Development Tools Module. [2]
• IBM provides the latest compilers and libraries via the Advance Toolchain. [3]
Compatibility and New Features on Power10
• Applications compiled with earlier versions of GCC to run on POWER8 or
POWER9 processors will run compatibly on Power10 processors.
• GCC 11.2 or later is recommended to exploit all new features available in
Power ISA 3.1 and implemented in Power10 processors.
• GCC 11.2 provides access to the Matrix Multiply Assist (MMA) feature
provided by Power10 processors.
[5]
• MMA programs can be compiled using any of the GCC, LLVM, and Open XL
compilers, provided you use sufficiently recent releases.
Languages
• C (gcc), C++ (g++), and Fortran (gfortran), along with others such as Go
(gccgo), D (gdc), and Ada (gnat).
• Only gcc, g++, and gfortran are usually installed by default.
• The golang compiler
[4] is the preferred alternative for building Go programs
on Power.
IBM Advance Toolchain
• The Advance Toolchain provides Power-optimized system libraries along
with the compilers, debuggers, and other tools.
• Building code with the Advance Toolchain can produce the most highly
optimized code possible on the latest processors.
IBM Recommended and Supported Compiler Flags
[6]
-O3 or -Ofast
Aggressive optimization. -Ofast is essentially equivalent to -O3
-ffast-math, which also relaxes restrictions on IEEE floating-
point arithmetic.
-mcpu=power n
Compile using instructions supported by the Powern processor.
For example, to use instructions available only on Power10,
select -mcpu=power10.
-flto
Optional. Perform “link-time” optimization. This optimizes code
across function calls where the caller and called functions exist
in different compilation units, and can often provide a significant
performance boost.
-funroll-loops
Optional. Perform more aggressive duplication of loop bodies
than the compiler normally would. Generally you should omit
this, but on some codes this can provide better performance.
Note:
Although -mcpu=power10 is supported as early as GCC 10.3, GCC 11.2 is preferred
because earlier compilers don’t support every feature implemented in the Power10
processors. Also, objects created using -mcpu=power10 will not run on POWER9 or
earlier processors! However, there are ways to create code that is optimized for
different processor versions.
[7]
[1] Red Hat: Using GCC Toolset. https://access.redhat.com/documentation/en-
us/red_hat_enterprise_linux/8/html/developing_c_and_cpp_applications_in_rhel_8/gcc-toolset_toolsets.
[2] SUSE: Understanding the Development Tools Module. https://www.suse.com/c/suse-linux-essentials-
where-are-the-compilers-understanding-the-development-tools-module/.
[3] Advance Toolchain for Linux on IBM Power Systems. https://www.ibm.com/support/pages/advance-
toolchain-linux-power.
[4] Go Language. https://golang.org.
[5] Matrix-Multiply Assist Best Practices Guide.
http://www.redbooks.ibm.com/redpapers/pdfs/redp5612.pdf.
[6] Using the GNU Compiler Collection. https://gcc.gnu.org/onlinedocs/gcc.pdf.
[7] Target-Specific Optimization with the GNU Indirect Function Mechanism.
https://developer.ibm.com/tutorials/optimized-libraries-for-linux-on-power/#target-specific-optimization-
with-the-gnu-indirect-function-mechanism.