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Teach the local allocator to know that live-in values (e.g. arguments) are

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live at function entry.  This prevents it from using arg registers for other
purposes before the arguments are used.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28809 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-06-15 22:21:53 +00:00
parent 8e173de059
commit 44500e3d53
1 changed files with 20 additions and 0 deletions
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20
lib/CodeGen/RegAllocLocal.cpp
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@ -491,6 +491,26 @@ void RA::AllocateBasicBlock(MachineBasicBlock &MBB) {
// loop over each instruction
MachineBasicBlock::iterator MII = MBB.begin();
const TargetInstrInfo &TII = *TM->getInstrInfo();
// If this is the first basic block in the machine function, add live-in
// registers as active.
if (&MBB == &*MF->begin()) {
for (MachineFunction::livein_iterator I = MF->livein_begin(),
E = MF->livein_end(); I != E; ++I) {
unsigned Reg = I->first;
PhysRegsEverUsed[Reg] = true;
PhysRegsUsed[Reg] = 0; // It is free and reserved now
PhysRegsUseOrder.push_back(Reg);
for (const unsigned *AliasSet = RegInfo->getAliasSet(Reg);
*AliasSet; ++AliasSet) {
PhysRegsUseOrder.push_back(*AliasSet);
PhysRegsUsed[*AliasSet] = 0; // It is free and reserved now
PhysRegsEverUsed[*AliasSet] = true;
}
}
}
// Otherwise, sequentially allocate each instruction in the MBB.
while (MII != MBB.end()) {
MachineInstr *MI = MII++;
const TargetInstrDescriptor &TID = TII.get(MI->getOpcode());