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Speed up this loop a bit, based on some observations that Nate made, and

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add some comments.  This loop really needs to be reevaluated!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22966 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-08-22 16:55:22 +00:00
parent ce5fcc30ae
commit f8355d9846
1 changed files with 34 additions and 8 deletions
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42
lib/CodeGen/RegAllocLinearScan.cpp
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@ -603,6 +603,8 @@ void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
unsigned RA::getFreePhysReg(LiveInterval* cur)
{
std::vector<unsigned> inactiveCounts(mri_->getNumRegs(), 0);
unsigned MaxInactiveCount = 0;
for (IntervalPtrs::iterator i = inactive_.begin(), e = inactive_.end();
i != e; ++i) {
unsigned reg = i->first->reg;
@ -610,19 +612,43 @@ unsigned RA::getFreePhysReg(LiveInterval* cur)
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
++inactiveCounts[reg];
MaxInactiveCount = std::max(MaxInactiveCount, inactiveCounts[reg]);
}
const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
unsigned freeReg = 0;
for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_),
e = rc->allocation_order_end(*mf_); i != e; ++i) {
unsigned reg = *i;
if (prt_->isRegAvail(reg) &&
(!freeReg || inactiveCounts[freeReg] < inactiveCounts[reg]))
freeReg = reg;
unsigned FreeReg = 0;
unsigned FreeRegInactiveCount = 0;
// Scan for the first available register.
TargetRegisterClass::iterator I = rc->allocation_order_begin(*mf_);
TargetRegisterClass::iterator E = rc->allocation_order_end(*mf_);
for (; I != E; ++I)
if (prt_->isRegAvail(*I)) {
FreeReg = *I;
FreeRegInactiveCount = inactiveCounts[FreeReg];
break;
}
// If there are no free regs, or if this reg has the max inactive count,
// return this register.
if (FreeReg == 0 || FreeRegInactiveCount == MaxInactiveCount) return FreeReg;
// Continue scanning the registers, looking for the one with the highest
// inactive count. Alkis found that this reduced register pressure very
// slightly on X86 (in rev 1.94 of this file), though this should probably be
// reevaluated now.
for (; I != E; ++I) {
unsigned Reg = *I;
if (prt_->isRegAvail(Reg) && FreeRegInactiveCount < inactiveCounts[Reg]) {
FreeReg = Reg;
FreeRegInactiveCount = inactiveCounts[Reg];
if (FreeRegInactiveCount == MaxInactiveCount)
break; // We found the one with the max inactive count.
}
}
return freeReg;
return FreeReg;
}
FunctionPass* llvm::createLinearScanRegisterAllocator() {