Skip to content
Switch branches/tags
Go to file
Cannot retrieve contributors at this time

OMR Compiler Options

The OMR Compiler Technology provides a number of options that allow you to take some control over its run-time behavior. This document contains the following:

Setting options

OMR Compiler options are either set through command line options or environment variables. If the OMR Compiler is being used as part of a language VM then the options can only be set through the VM command line arguments using the -Xjit argument followed by the options, or through environment variables in some cases, such as TR_dumpGraphs.

Compiler options may be set using the TR_Options environment variable, for example:

TR_Options='traceFull,log=log' ./testjit

Language environments may also accept options on their command-line, but the implementation is environment-specific. For example, the OpenJ9 Java VM accepts JIT command-line options as:

java -Xjit:count=0,traceFull,log=log HelloWorld

Option Sets

It is possible to apply a set of compiler options ("option sets") to a specific method or group of methods. Furthermore, it is possible to apply different option sets to different (groups of) methods. An option set can be defined on the command line by enclosing the desired set of parameters in parentheses and preceding it with a method filter expression in braces. For example, to apply the option set count=0,optlevel=hot only to the method that matches the signature HelloWorld.main([Ljava/lang/String;)V add the following to the TR_Options environment variable or -Xjit command-line:


The option example below makes the compiler compile all methods at the warm optimization level, and traces the compilation of all method signatures that start with Frobnicate and Brobnicate in two different log files.


Option sets can also be defined in a limit file, if one is used, by adding a non-zero integer immediately after the initial plus sign on the line with the selected method(s). The integer corresponds to the option set number which can be set on the command line in lieu of a method filter expression.

For example, to apply count=0,optLevel=hot to method HelloWorld.main([Ljava/lang/String;)V, you could assign the number 1 to the option set in the command line:


and have the line corresponding to the method in the limit file beginning with +1:

+1 (hot) HelloWorld.main([Ljava/lang/String;)V @ 0x10C11DA4-0x10C11DDD

Note that some parameters are always applied globally and are illegal within option sets. The compiler will fail to start up if an option set contains such parameters.

Options list

This section contains a subset of options available for controlling the runtime behavior of the compiler. This section does not exhaustively list all the options or their categories. To see all of the available options to control the compiler, please see the options listed in <omr-root-dir>/compiler/control/OMROptions.cpp and <omr-root-dir>/compiler/env/FEBase.cpp

The purpose of listing the options in this document is to give you an insight into the level of control you have over the compiler through the options rather than acting as a reference. The options are categorized in subsections to help you understand the general pattern (eg. optimizer-specific options, trace-specific options, etc).

Code Generation Options

Option Description
bcLimit=nnn bytecode size limit
code=nnn code cache size, in KB
codetotal=nnn total code memory limit, in KB
noExceptions fail compilation for methods with exceptions
noregmap generate GC maps without register maps

Optimization Options

Option Description
acceptHugeMethods allow processing of really large methods
count=nnn number of invocations before compiling methods without loops
disableCFGSimplification disable Control Flow Graph simplification
disableDeadTreeElimination disable dead tree elimination
disableGlobalDSE disable global dead store elimination
disableGRA disable IL based global register allocator
disableInlining disable IL inlining
disableLiveRegisterAnalysis disable live register analysis
disableLoopUnroller disable loop unroller
disableOpts={regex} list of optimizations to disable
disableOptTransformations={regex} list of optimizer transformations to disable
disableTreeCleansing disable tree cleansing
disableVirtualInlining disable inlining of virtual methods
dontInline={regex} list of methods to not inline
firstOptIndex=nnn index of the first optimization to perform
firstOptTransformationIndex=nnn index of the first optimization transformation to perform
ignoreIEEE allow non-IEEE compliant optimizations
insertDebuggingCounters=nnn Insert instrumentation for debugging counters
lastOptIndex=nnn index of the last optimization to perform
lastOptTransformationIndex=nnn index of the last optimization transformation to perform
numRestrictedGPRs=nnn number of restricted GPRS (0-5). Currently z only
onlyInline={regex} list of methods that can be inlined
optLevel=level compile all methods at specified level (cold, warm, hot, veryHot, scorching)
paranoidOptCheck check the trees and cfgs after every optimization phase

Logging and Trace Options

Option Description
debugCounters= Activate dynamic Debug counters
firstVlogLine=nnn first vlog line to be written
lastVlogLine=nnn last vlog line to be written
log=filename write log output to filename
optDetails log all optimizer transformations
stats dump statistics at end of run
traceBC dump bytecodes
traceBin dump binary instructions
traceBlockSplitter trace block splitter
traceCG dump output of code generation passes
traceFull turn on all trace options
traceGlobalDSE trace global dead store elimination
traceInlining trace IL inlining
traceOpts={regex} list of optimizations to trace
traceOptTrees dump trees after each optimization
tracePRE trace partial redudndancy elimination
traceRedundantMonitorElimination trace redundant monitor elimination
traceRegisterPressureDetails include extra register pressure annotations in register pressure simulation and tree evaluation traces
traceTrees dump trees after each compilation phase
verbose write compiled method names to vlog file or stdout in limitfile format
verbose={regex} list of verbose output to write to vlog or stdout
version display the jit build version
vlog=filename write verbose output to filename

Debugging Options

Option Description
breakAfterCompile raise trap when method compilation ends
breakBeforeCompile raise trap when method compilation begins
breakOnBBStart raise trap on BBStarts of method
breakOnCreate={regex} raise trap when creating an item whose name (given by enumerate) matches regex
breakOnEntry insert entry breakpoint instruction in generated code
breakOnLoad break after the options have been processed
breakOnOpts={regex} raise trap when performing opts with matching regex
debugBeforeCompile invoke the debugger when method compilation begins
debugOnEntry invoke the debugger at the entry of a method
exclude=xxx do not compile methods beginning with xxx
limit=xxx only compile methods beginning with xxx
maskAddresses remove addresses from trace file
noRecompile do not recompile even when counts allow it
stopOnFailure stop compilation if exceed memory threshold
tlhPrefetch enable software prefetch on allocation for X86
tossCode throw code and data away after compiling