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Speed up this loop a bit, based on some observations that Nate made, and
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
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@ -603,6 +603,8 @@ void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
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unsigned RA::getFreePhysReg(LiveInterval* cur)
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{
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std::vector<unsigned> inactiveCounts(mri_->getNumRegs(), 0);
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unsigned MaxInactiveCount = 0;
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for (IntervalPtrs::iterator i = inactive_.begin(), e = inactive_.end();
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i != e; ++i) {
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unsigned reg = i->first->reg;
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@ -610,19 +612,43 @@ unsigned RA::getFreePhysReg(LiveInterval* cur)
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"Can only allocate virtual registers!");
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reg = vrm_->getPhys(reg);
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++inactiveCounts[reg];
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MaxInactiveCount = std::max(MaxInactiveCount, inactiveCounts[reg]);
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}
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const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
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unsigned freeReg = 0;
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for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_),
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e = rc->allocation_order_end(*mf_); i != e; ++i) {
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unsigned reg = *i;
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if (prt_->isRegAvail(reg) &&
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(!freeReg || inactiveCounts[freeReg] < inactiveCounts[reg]))
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freeReg = reg;
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unsigned FreeReg = 0;
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unsigned FreeRegInactiveCount = 0;
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// Scan for the first available register.
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TargetRegisterClass::iterator I = rc->allocation_order_begin(*mf_);
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TargetRegisterClass::iterator E = rc->allocation_order_end(*mf_);
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for (; I != E; ++I)
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if (prt_->isRegAvail(*I)) {
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FreeReg = *I;
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FreeRegInactiveCount = inactiveCounts[FreeReg];
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break;
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}
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// If there are no free regs, or if this reg has the max inactive count,
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// return this register.
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if (FreeReg == 0 || FreeRegInactiveCount == MaxInactiveCount) return FreeReg;
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// Continue scanning the registers, looking for the one with the highest
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// inactive count. Alkis found that this reduced register pressure very
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// slightly on X86 (in rev 1.94 of this file), though this should probably be
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// reevaluated now.
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for (; I != E; ++I) {
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unsigned Reg = *I;
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if (prt_->isRegAvail(Reg) && FreeRegInactiveCount < inactiveCounts[Reg]) {
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FreeReg = Reg;
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FreeRegInactiveCount = inactiveCounts[Reg];
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if (FreeRegInactiveCount == MaxInactiveCount)
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break; // We found the one with the max inactive count.
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}
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}
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return freeReg;
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return FreeReg;
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}
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FunctionPass* llvm::createLinearScanRegisterAllocator() {
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