In allocateRegisters() and allocateRegistersMinimal(), we iterate through RefPositions and update regsToFree, delayRegsToFree, regsToMakeInactive, delayRegsToMakeInactive and copyRegsToFree. These are regMaskTP local variables and as such incurs significant regression with more than 64 registers.

This primarily applies to the following

    regMaskTP    regsToFree              = RBM_NONE;
    regMaskTP    delayRegsToFree         = RBM_NONE;
    regMaskTP    regsToMakeInactive      = RBM_NONE;
    regMaskTP    delayRegsToMakeInactive = RBM_NONE;
    regMaskTP    copyRegsToFree          = RBM_NONE;

In order to optimize the operations on these variables, they can be represented by

    struct RegSetMasks
    {
        SingleTypeRegSet    regsToFree              = RBM_NONE;
        SingleTypeRegSet    delayRegsToFree         = RBM_NONE;
        SingleTypeRegSet    regsToMakeInactive      = RBM_NONE;
        SingleTypeRegSet    delayRegsToMakeInactive = RBM_NONE;
        SingleTypeRegSet    copyRegsToFree = RBM_NONE;
    };

and declared as one of following

Option A

    RegSetMasks lowRegSet;
    RegSetMasks highRegSet;
    RegSetMasks *currRegSet = &lowRegSet;

Option B

  RegSetMasks intRegSet;
  RegSetMasks fltRegSet;
  RegSetMasks mskRegSet;

This will reduce the overhead due to operations on regMaskTP since we will be working on SingleTypeRegSet which is a uint64.

Methods from the list of regressed methods this is likely to improve

• allocateRegisters()
• allocateRegistersMinimal()
• freeRegisters()

The effect of switching to more than 64 registers for these methods without an optimization based on profiling is shown below.