1. HPC User Forum: Back-End Compiler Technology Panel
Luiz DeRose
Programming Environment Director
Cray Inc.

2. Luiz DeRose (ldr@cray.com) © Cray Inc.
Are compiler code generation techniques going to transition along with the hardware transition from multi-core to many-core and hybrid systems and at what speed?
Multi-core to many-core
The hard part is determining if it can go 2-wide
From there, going n-wide is straightforward
The next release of the Cray Compiler will support Automatic Parallelism for “n-Cores”
Hybrid systems will take more work and more time
April 21, 2009
Luiz DeRose © Cray Inc.

3. Luiz DeRose (ldr@cray.com) © Cray Inc.
What information do you need from a Compiler Intermediate Format to efficiently utilize multi-core, many-core and hybrid systems that is not available from traditional languages like C, C++, or F90? Are you looking at directive-based or library-based approaches or is there another approach that you like?
The parallelism concepts should be fully-integrated into the IR
UPC and CAF need to be optimized like any ordinary references
OpenMP needs to be treated as part of the language, not as an add-on
Our approach is:
Fully automatic utilization of parallel resources, whatever and wherever they are
Use of language extensions (e.g. UPC) to guide this parallelization
Use of directives as necessary for tuning, parallel placement, and OpenMP
Use of user-called libraries as a last resort
But fully automatic is our principal approach, without the need for hand-inserted directives or library calls
April 21, 2009
Luiz DeRose © Cray Inc.

4. Luiz DeRose (ldr@cray.com) © Cray Inc.
Is embedded global memory addressing (like Co-Array Fortran) to be widely available and supported even on distributed memory systems?
YES! (after all, we invented it!)
UPC & CoArray Fortran are already fully optimized and integrated into the Cray Compiler
No preprocessor involved
The Cray X86 Compiler already supports the proposed Fortran 2008 Co-Arrays
April 21, 2009
Luiz DeRose © Cray Inc.

5. Luiz DeRose (ldr@cray.com) © Cray Inc.
What kind of hybrid systems or processor extensions are going to be supported by your compiler's code generation suite?
yes
April 21, 2009
Luiz DeRose © Cray Inc.

6. Luiz DeRose (ldr@cray.com) © Cray Inc.
What new run-time libraries will be available to utilize multi-core, many-core, and hybrid systems and will they work seamlessly through dynamic linking?
OpenMP supports nested parallelism and, depending on the application, scales nicely
Automatic Parallelism on the Cray X86 Compiler interacts with the OpenMP runtime library
Dynamic linking tends to have a negative impact on performance, sometimes very significantly
However, we have in our road map to support DSO
So, it will be available for those users that are willing to take the performance hit,
April 21, 2009
Luiz DeRose © Cray Inc.