Enable high-performing z/OS XL C/C++ programs for optimized business software solutions

IBM® z/OS® V1.11 XL C/C++

Highlights

Deliversperformance

improvementsoverz/OSV1.10XL

C/C++byexploitingthelatest

advancementsinoptimization

andhardwaretechnology

Leveragessystemprogramming

capabilitieswithnewsub-options

totheMETALCPROLOGand

EPILOGcompileroptions

Exploitstheflexibilityandpower

ofmodule-leveldebuggingwith

thenewdebugutilityCDADBGLD

andsource-leveldebuggingwith

thenewdbgld–coption

Reducesapplicationeffortand

improvesproductivitythrough

newcompileroptions

software

The IBM z/OS XL C/C++ compiler

is designed to help you create and

maintain critical business applications

written in C or C++, maximize

application performance, and

improve developer productivity. The

IBM z/OS XL C/C++ compiler can

transform C or C++ source code to

fully exploit IBM System z® hardware.

Enhanced features help you leverage

hardware advancements through

built-in functions, performance-tuned

libraries, and language constructs

that simplify system programming

and boost application run time

performance.

IBM works constantly to improve

compiler components, including front-

ends, high-level optimizers, and low-

level optimizers. By upgrading your

compiler, you can keep up with new

language standards and extensions,

advancements in hardware

technology, usability features,

and advances in optimization with

minimal or no source code changes.

Compilers offer a cost-effective way

to get more out of existing technology

and stay ahead of competitors on the

technology curve.

.

Delivers application perform-ance improvements by exploiting System z hardware The z/OS V1.11 XL C/C++ compiler

exploits System z10 hardware through

the PREFETCH option. This option

enables heuristics to automatically

generate System z10 prefetch data

instructions as appropriate. This can

help reduce effects of memory latency

by beginning to fetch data before it is

needed. Additional optimization and

tuning improvements have been made

for the compiler including inlining of

additional destructors to avoid over-

head of function calls. These changes

can improve the performance of

generated code without the need for

changes to the source code. A

performance improvement of over 8%

was observed using code generated

using the z/OS V1.11 XL C/C++ com-

piler with high optimization compared

to code generated using the z/OS V1.10

XL C/C++ compiler1.

Large page (1 MB) support in both

Java™ and Language Environment®

means applications using JVM and XL

C/C++ (in AMODE64) can benefit from

improved memory management.

The new REPORT option makes it

easier to know what types of optimiza-

tion were performed. This option pro-

duces pseudo-C code listings which

show how sections of code have been

optimized in both the IPA-compile and

IPA-bind step, to help you understand

compiler optimizations and tune appli-

cation code for better performance.

Exploits flexibility and power of

module-level debugging and source-

level debugging

In z/OS V1.11 XL C/C++, you now gain

the flexibility and power of module-level

debugging in batch mode through the

new CDADBGLD MVS utility instead of

using z/OS UNIX® System Services.

In addition, the dbgld z/OS UNIX

System Services utility has been

enhanced with a new –c option that

includes the source code of the pro-

gram within the debug information in a

debug side file. This makes it possible

to step through the program even

when the original source code is not

available at debugging time, as might

occur on a production system when

the source code resides on a different

system used for development.

These two utilities enable IBM Debug

Tool and z/OS dbx to exploit deferred

loading of debug information, greatly

improving debugger load time.

Reduces application effort and

improves productivity with new

compiler options

z/OS XL C/C++ continually strives to

improve usability to make it easier for

you to work with the compiler, and thus

be more productive.

The MAKEDEP option reduces the

complexity of builds and streamlines the

build process by analyzing source files

and determining source dependencies.

The SHOWMACROS compiler option

controls how macro definitions are

emitted within preprocessor output

(PPONLY option or –E), to make it

easier for you to debug complex macro

expansions and to determine which

feature test macros are in effect.

The RTCHECK compiler option

instructs the compiler to exploit com-

pare-and-trap instructions for specific

run time checks. Valid sub-options are:

• BOUNDS, to trap when subscript-

ing past the boundaries of objects of

known size

• DIVZERO, to trap on integer divide-

by-zeros

• NULLPTR, to trap on an attempt to

dereference a null pointer

• ALL, all of the above

1. This is based on internal IBM lab measurements using the ILP32, XPLINK, ARCH(8), TUNE(8), HGPR, O3, HOT, and IPA(LEVEL(2)) with PDF compiler options. Performance results for specific applications will vary; some factors affecting performance are the source code and the compiler options specified.

2

The SKIPSRC compiler option improves

the readability of the source listing by

excluding non-compiled statements

from compiler listings, for example,

code which is “#ifdef’ed out”. SKIPSRC

makes it easier to look at the listings

and understand them, which can be

very beneficial when working with

header files and source files with large

segments of non-compiled code.

Enables system programming using

Metal C

System programming allows for devel-

opment of freestanding programs that

do not depend on any supplied run

time environment, such as Language

Environment. These programs obtain

the system services that they need by

calling assembler services directly.

You can use the Metal C feature of z/OS

XL C in place of assembler for devel-

opment of system programs. Metal C

includes the following capabilities:

• The __asm keyword allows you to

specify assembly instructions in

C code.

• The METAL compiler option allows

you to use the MVS system linkage

conventions.

• The PROLOG and EPILOG compiler

options and the #pragma prolog()

and #pragma epilog() preprocessor

directives allow you to specify

custom HLASM prolog and epilog

code, to implement custom function

linkage conventions if required.

System programs (written in C) exploit

the same advancements in hardware

and advances in performance optimi-

zation realized by application programs

coded in C.

z/OS V1.11 XL C/C++ delivers new

sub-options to the existing METAL

C PROLOG and EPILOG compiler

options:

• The EXTERN sub option indicates

that the PROLOG/EPILOG code is to

apply only to functions with

external linkage.

• The ALL sub option indicates that the

PROLOG/EPILOG code is to apply to

both external linkage and static link-

age functions.

Leverages the decimal floating-

point unit

It is estimated that 55 percent of

numeric data in commercial databases

is decimal data. Traditional floating-

point arithmetic is not sufficient for

commercial software. It often leads to

unexpected results for values that are

inherently decimal, such as monetary

values and percentages. Currently,

many decimal arithmetic calculations

are carried out in software, which is

typically estimated to be 10 to 100

times slower than hardware.

IBM z10 processors now leverage a

decimal floating-point (DFP) unit. This

is designed to bring significant per-

formance and accuracy improvements

to commercial software that operates

on decimal data. The z/OS XL C/C++

compiler exploits the DFP unit.

Enables easier porting of C/C++ appli-

cations to z/OS

To facilitate porting to z/OS XL C/C++,

our latest z/OS V1.11 XL C/C++ compiler

supports code that exploits Unicode

literals and character types, and also

adds two new features enhancing GCC

compatibility: GCC statement expres-

sion constructs and zero-extent

array members.

z/OS V1.11 XL C/C++ enhances the

Standard C++ Library with selected

features of the Technical Report on C++

Library Extensions (TR1).

In addition, this release of the compiler

introduces support for a number of

selected features of the emerging C++0x

standard including extended friend dec-

larations, external templates and name

lookup in template base class.

3

Figure1: z10 processor.

Get more return on your IT investment

The IBM z/OS XL C/C++ compiler

bridges your applications with the

hardware architectures, doing the

heavy lifting for you, hiding the increas-

ing complexities of processor architec-

ture, and greatly improving developer

productivity. By relying on the compiler,

you can concentrate on high value

tasks, creating better quality and better

performing applications.

State-of-the-art compilation technology

enables you to exploit new features

found in the latest hardware with

minimal source code changes. The

compiler determines the best way to

transform and optimize code genera-

tion for the systems your applications

will run on.

Standards compliance

The IBM z/OS XL C/C++ compiler con-

forms to ISO C89 and C99 standards.

The compiler also supports C++98

with the 2003 Technical Corrigendum

1 updates. To handle applications with

mixed C and C++ code and to include

header files that contain C99 language

constructs, XL C++ also supports a

subset of C99.

Augmenting the standardized lan-

guage levels, the IBM z/OS XL C/C++

compiler has implemented selected

GNU C and C++ language extensions.

The z/OS XL C/C++ compiler has also

introduced a subset of C++0x, the

working draft of the next C++ pro-

gramming standard, by implementing

features frequently requested by users.

Provides powerful, no hassle applica-

tion programming

Well written and thoroughly debugged

code, fully conformant to its language

standard, can take maximum advan-

tage of the optimizing technology in

IBM z/OS XL C/C++ for a potential

dramatic increase in performance.

The optimization and hardware feature

support in IBM z/OS XL C/C++ can

improve your productivity as the com-

piler can generate code that exploits

the leading-edge performance in new

hardware, often with minimal source

code changes.

IBM z/OS XL C/C++ supports several

levels of increasingly aggressive code

transformations. Advanced optimization

techniques, such as inter-procedural

analysis (IPA) and profile-directed

feedback (PDF), are available at high

levels of optimization that can result

in significant performance improve-

ments. IPA analyzes and optimizes

your application as a whole, rather than

on a file-by-file basis. PDF generates

information that instructs the optimizer

to focus on trade-offs that favor code

that executes more frequently.

Flexible compiler architecture

The following series of component

diagrams illustrate how compiling at

various optimization levels affects the

compiler transformation of source code

into executables. Compile-time options

allow you to inform the compiler of your

preferences for balancing the trade-

offs for high application performance:

precision, code size, compilation time,

and system resources.

What happens at NOOPT

Compiling at NOOPT, the default opti-

mization level, the compiler checks the

application source code for algorithmic

correctness, exposes problems such

as uninitialized variables and improper

casting, and saves all debug informa-

tion. The intermediate code generated

from the compiler front-end passes

directly to the back-end, where basic

optimizations such as redundant code

elimination and constant folding are

performed before binding. Specifying

-qarch with –qnoopt sets the target

architecture for the application and

can result in better performance as

the compiler exploits features of the

target architecture. A clean compi-

lation at NOOPT signifies that the

compiler has structured the source

code to take advantage of -qarch and

-qtune settings at higher -O levels. The

–qarch and –qtune options instruct the

compiler to generate code for optimal

execution on a given microprocessor

or architectural family.

4

What happens at -O2

Recompiling at –O2 exposes the

source code to comprehensive low-

level transformations that apply to the

subprogram or compilation unit scope.

At –O2, the compiler back-end per-

forms, for example, more optimizations

on loops, and identifies and removes

unnecessary code constructs and

redundant computations. The compiler

strives to balance improved perform-

ance while limiting the impact on com-

pilation time and system resources. The

target architecture, indicated by –qarch

and –qtune, is more important at –O2,

as the compiler optimizes to exploit the

features of the hardware.

What happens at -O3

Recompiling at –O3 provides more

intense low-level transformations

that removes many of the limitations

present at –O2. Optimizations at –O3

encompass larger program regions

and attempt more in-depth analysis,

while balancing the trade-offs in com-

pilation time and memory resources.

While not all applications contain

opportunities for the optimizer to pro-

vide a measurable increase in perform-

ance, most applications can benefit

from this kind of analysis.

5

Figure2: Compiling at –noopt or –O2.

Generates

C front-end C++ front-end

Back-end Optimizedobjects Other objects

Output

Intermediate language

Intermediatelanguage

Binder

Module and DLL

What happens at -O4

Optimization at –O4 builds on that

of –O3 by triggering inter-procedural

analysis (IPA), which strives to optimize

the entire application as a unit. With IPA

specified on both the compile and bind

steps, the compiler performs multiple

iterations through the optimizer and the

back-end, with trade-offs in compile

time, especially on the bind step. Appli-

cations that contain many frequently

used routines are most likely to benefit

from IPA. Profile-directed feedback

(PDF), which iteratively refines a profile

of how often branches are taken

and blocks of code are executed in

the application, requires IPA. PDF is

designed to tune an application for a

particular usage scenario.

What happens at -O5

The highest optimization level cur-

rently available to the z/OS XL C/C++

compiler is -O5. This initiates aggres-

sive optimization and the highest level

of inter-procedural analysis currently

available. The -O5 optimization proc-

ess begins with the front-end emitting

an intermediate language which IPA

6

Figure3: Compiling at –O3.

Generates

Back-end Optimizedobjects Other objects

Output

Binder

Module and DLL

Optimizer

C front-end C++ front-end

Intermediate languageIntermediate

language

1

Yes

No

Compile step

Legend

Bind step

Optimizer Libraries PDF information(instrumented runs)

Partitions

Back-end Optimizedobjects Other objects

Output

IPA objects

2

Optimizedobjects Other objects

Output

Program isbound with-O4 or -O5?

Binder

Module and DLL

Generates

C front-end C++ front-end

Intermediate languageIntermediate

language

Intermediatelanguage

Intermediatelanguage

Intermediatelanguage

Intermediate language

Intermediate language

Figure4: Compiling at –O4 and –O5.

7

analyzes and transforms. The opti-

mized intermediate language is then

processed by the low-level optimizing

back-end for further optimization and

object code creation.

Compilation at –O5 builds on the

optimizations at –O4, adding deeper

whole-program analysis. Most aggres-

sive transformations are available at

-O5, and the compiler makes full use

of loop optimizations and the assump-

tions resulting from IPA.

License options

To help you optimize software licensing

costs, IBM can assist in identifying the

licenses that best suits your organization.

For additional information on the types of

licenses available for z/OS, see:

http://www-03.ibm.com/systems/z/

resources/swprice/index.html

Ordering Information:

IBM z/OS XL C/C++ is an optional

priced feature of z/OS. z/OS XL C/

C++ is available through the Shopz-

Series web site:

https://www14.software.ibm.com/

webapp/ShopzSeries/ShopzSeries.jsp

where it is listed as “z/OS V1 C/C++

without Debug”.

For more information:To learn more about z/OS V1.11 XL

C/C++, contact your IBM representa-

© Copyright IBM Corporation 2009

IBM Corporation Software Group Route 100 Somers, NY 10589 U.S.A.

Produced in the United States of America 10-09

All Rights Reserved

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UNIX is a registered trademark of The Open Group

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The information contained in this publication is

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efforts were made to verify the completeness

and accuracy of the information contained in this

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Nothing contained in this publication is intended to,

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Feature Benefit

• Exploitsz/Architecture®

Industry language standards compliance

• Facilitatesportingfromoneplatformtoanother.•�ro�i�es compiler �iagnostics to help�ro�i�escompiler�iagnosticstohelpyouachie�ethele�elofconformanceyouwanttoaparticularprogramminglan-guagestan�ar�.•�upports commonly use� ���� an� non-�upportscommonlyuse�����an�non-����languageextensions.

Industry-leading optimizers •Usestechnologyfromthein�ustry-lea�-ing����XLC/C++familyofcompilers,z/O�XLC/C++is�esigne�tooffersu-periorapplicationperformanceonz/O�.

Improved debug information & debug APIs

•Enablestoolpro�i�ers(inclu�ing����DebugTool,Application�erformanceAnalyzer,z/O��bx,aswellasthir�-partytools)tobuil�a��itionalcapabilityan�impro�e�performanceintheirtools.

Improved low-level programming support

•�ro�i�essystemprogrammingcapabilitiesthrough��etalC.With��etalCyoucaninsertHLA���instructionsintoCsource,specifycustomfunctionprologsan�epilogs,an�generateHLA���source,makingiteasiertointegratenewco�ewithexistingHLA���programs.

Exploits hardware support for IEEE 754 decimal floating-point data

•�mpro�estheaccuracyan�performanceof�ecimalfloating-pointcalculationsforcommercialapplications.

Built-in functions •�ro�i�esaccesstothenewestan�mostefficienthar�wareoperationsatthesourcele�el.•�implifiesthe�e�elopmenteffortforcreatingan�maintaininghigh-perfor-manceapplications.

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tive or IBM Business Partner, or visit the

z/OS XL C/C++ Web site at www.ibm.

com/software/awdtools/czos

IBM Service and SupportThe IBM Service and Support

organization is dedicated to providing

responsive platform and cross-plat-

form software support that meets or

exceeds customer expectations. For

complex or code-related problems,

specialized service teams work with

subject matter experts in compiler

development to provide a level of

support excellence that benefits IBM,

a longstanding leader in information

technology. To learn more about sup-

port, visit the z/OS XL C/C++ support

Web site at www.ibm.com/software/

awdtools/czos/support

Designed for IBM platforms

Figure5: Summary of z/OS XL C/C++ compiler features and benefits.