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Disable physical register coalescing when the number of live ranges for the

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physreg becomes ridiculously high.

std::upper_bound may be log(N), but for sufficiently large live intervals, it
becomes log(N)*cachemiss = a long long time.

This patch improves coalescer time by 4500x for a function with 20000
function calls. The generated code is different, but not significantly worse -
the allocator hints are almost as good as physreg coalescing anyway.

llvm-svn: 98023
This commit is contained in:
Jakob Stoklund Olesen 2010-03-09 00:59:48 +00:00
parent 4995bb0450
commit 3d0157ae7e
1 changed files with 12 additions and 0 deletions
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12
lib/CodeGen/SimpleRegisterCoalescing.cpp
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@ -1671,8 +1671,20 @@ bool SimpleRegisterCoalescing::JoinCopy(CopyRec &TheCopy, bool &Again) {
// density, do not join them, instead mark the physical register as its
// allocation preference.
LiveInterval &JoinVInt = SrcIsPhys ? DstInt : SrcInt;
LiveInterval &JoinPInt = SrcIsPhys ? SrcInt : DstInt;
unsigned JoinVReg = SrcIsPhys ? DstReg : SrcReg;
unsigned JoinPReg = SrcIsPhys ? SrcReg : DstReg;
// Don't join with physregs that have a ridiculous number of live
// ranges. The data structure performance is really bad when that
// happens.
if (JoinPInt.ranges.size() > 1000) {
mri_->setRegAllocationHint(JoinVInt.reg, 0, JoinPReg);
++numAborts;
DEBUG(dbgs() << "\tPhysical register too complicated, abort!\n");
return false;
}
const TargetRegisterClass *RC = mri_->getRegClass(JoinVReg);
unsigned Threshold = allocatableRCRegs_[RC].count() * 2;
unsigned Length = li_->getApproximateInstructionCount(JoinVInt);