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Change the way we choose a free register: instead of picking the first

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free allocatable register, we prefer the a free one with the most uses
of inactive intervals. This causes less spills and performes a bit
better compared to gcc:

Program                 | GCC/LLC (Before)| GCC/LLC (After)
164.gzip/164.gzip       | 0.59            | 0.60
175.vpr/175.vpr         | 0.57            | 0.58
176.gcc/176.gcc         | 0.59            | 0.61
181.mcf/181.mcf         | 0.94            | 0.95
186.crafty/186.crafty   | 0.62            | 0.62
197.parser/197.parser   | 0.89            | 0.88
252.eon/252.eon         | 0.61            | 0.66
253.perlbmk/253.perlbmk | 0.79            | 0.84
254.gap/254.gap         | 0.81            | 0.81
255.vortex/255.vortex   | 0.92            | 0.93
256.bzip2/256.bzip2     | 0.69            | 0.69
300.twolf/300.twolf     | 0.91            | 0.90


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16147 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Alkis Evlogimenos 2004-09-02 21:23:32 +00:00
parent 679ff31e93
commit 84f5bcb013
1 changed files with 14 additions and 3 deletions
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17
lib/CodeGen/RegAllocLinearScan.cpp
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@ -522,15 +522,26 @@ void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
unsigned RA::getFreePhysReg(LiveInterval* cur)
{
std::vector<unsigned> inactiveCounts(mri_->getNumRegs(), 0);
for (IntervalPtrs::iterator i = inactive_.begin(), e = inactive_.end();
i != e; ++i) {
unsigned reg = (*i)->reg;
if (MRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
++inactiveCounts[reg];
}
const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
unsigned freeReg = 0;
for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
i != rc->allocation_order_end(*mf_); ++i) {
unsigned reg = *i;
if (prt_->isRegAvail(reg))
return reg;
if (prt_->isRegAvail(reg) &&
(!freeReg || inactiveCounts[freeReg] < inactiveCounts[reg]))
freeReg = reg;
}
return 0;
return freeReg;
}
FunctionPass* llvm::createLinearScanRegisterAllocator() {