GRA changes to reduce JIT overhead at warm opt levels

The commit introduces a new option -Xjit:graFreqThresholdAtWarm=<NNN>
that can be used to control the JIT overhead for compilations
performed at warm optimization level or below. The default value
of the threshold is 500. A larger value leads to lower JIT overhead
but also to potentially lower quality of the generated code.
For hot compilations or in situations where we think we can afford
more JIT overhead, the threshold is automatically set to 0.

Signed-off-by: Marius Pirvu <mpirvu@ca.ibm.com>

compiler/control/OMROptions.cpp

@@ -829,6 +829,8 @@ TR::OptionTable OMR::Options::_jitOptions[] = {
    {"GCRresetCount=",       "R<nnn>\tthe value to which the counter is reset to after being tripped by guarded counting recompilations (positive value)",
     TR::Options::setCount, offsetof(OMR::Options,_GCRResetCount), 0, "F%d"},
    {"generateCompleteInlineRanges", "O\tgenerate meta data ranges for each change in inliner depth", SET_OPTION_BIT(TR_GenerateCompleteInlineRanges), "F"},
+   {"graFreqThresholdAtWarm=", "O<nnn>\tgra threshold for block frequency for opt level less of equal to warm",
+        TR::Options::set32BitNumeric, offsetof(OMR::Options, _graFreqThresholdAtWarm), 500, "F%d"},
    {"help",               " \tdisplay this help information", TR::Options::helpOption, 0, 0, "F", NOT_IN_SUBSET},
    {"help=",              " {regex}\tdisplay help for options whose names match {regex}", TR::Options::helpOption, 1, 0, "F", NOT_IN_SUBSET},
    {"highCodeCacheOccupancyBCount=", "R<nnn>\tthe initial invocation count used during high code cache occupancy for methods with loops",
@@ -2678,6 +2680,7 @@ OMR::Options::jitPreProcess()
    _alwaysWorthInliningThreshold = 15;
    _maxLimitedGRACandidates = TR_MAX_LIMITED_GRA_CANDIDATES;
    _maxLimitedGRARegs = TR_MAX_LIMITED_GRA_REGS;
+   _graFreqThresholdAtWarm = 500;
    _counterBucketGranularity = 2;
    _minCounterFidelity = INT_MIN;
    _lastIpaOptTransformationIndex = INT_MAX;

compiler/control/OMROptions.hpp

@@ -1468,6 +1468,7 @@ class OMR_EXTENSIBLE Options
       _insertGCRTrees = false;
       _maxLimitedGRACandidates = 0;
       _maxLimitedGRARegs = 0;
+      _graFreqThresholdAtWarm = 0;
       _enableGPU = 0;
       _isAOTCompile = false;
       _jProfilingMethodRecompThreshold = 0;
@@ -1822,6 +1823,7 @@ class OMR_EXTENSIBLE Options
    int32_t getAlwaysWorthInliningThreshold() const { return _alwaysWorthInliningThreshold; }
    int32_t getMaxLimitedGRACandidates()   { return _maxLimitedGRACandidates; }
    int32_t getMaxLimitedGRARegs()         { return _maxLimitedGRARegs; }
+   int32_t getGRAFreqThresholdAtWarm()    { return _graFreqThresholdAtWarm; }
    int32_t getNumLimitedGRARegsWithheld();
 
    int32_t getProfilingCompNodecountThreshold()  { return _profilingCompNodecountThreshold; }
@@ -2481,6 +2483,7 @@ class OMR_EXTENSIBLE Options
 
    int32_t                     _maxLimitedGRACandidates;
    int32_t                     _maxLimitedGRARegs;
+   int32_t                     _graFreqThresholdAtWarm;
 
    int32_t                     _enableGPU;