New files
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5262 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/PHIElimination.cpp b/lib/CodeGen/PHIElimination.cpp
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+++ b/lib/CodeGen/PHIElimination.cpp
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+//===-- PhiElimination.cpp - Eliminate PHI nodes by inserting copies ------===//
+//
+// This pass eliminates machine instruction PHI nodes by inserting copy
+// instructions. This destroys SSA information, but is the desired input for
+// some register allocators.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/SSARegMap.h"
+#include "llvm/CodeGen/LiveVariables.h"
+#include "llvm/Target/MachineInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+
+namespace {
+ struct PNE : public MachineFunctionPass {
+ bool runOnMachineFunction(MachineFunction &Fn) {
+ bool Changed = false;
+
+ // Eliminate PHI instructions by inserting copies into predecessor blocks.
+ //
+ for (MachineFunction::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I)
+ Changed |= EliminatePHINodes(Fn, *I);
+
+ //std::cerr << "AFTER PHI NODE ELIM:\n";
+ //Fn.dump();
+ return Changed;
+ }
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addPreserved<LiveVariables>();
+ MachineFunctionPass::getAnalysisUsage(AU);
+ }
+
+ private:
+ /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions
+ /// in predecessor basic blocks.
+ ///
+ bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB);
+ };
+
+ RegisterPass<PNE> X("phi-node-elimination",
+ "Eliminate PHI nodes for register allocation");
+}
+
+const PassInfo *PHIEliminationID = X.getPassInfo();
+
+/// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in
+/// predecessor basic blocks.
+///
+bool PNE::EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB) {
+ if (MBB.front()->getOpcode() != TargetInstrInfo::PHI)
+ return false; // Quick exit for normal case...
+
+ LiveVariables *LV = getAnalysisToUpdate<LiveVariables>();
+ const TargetInstrInfo &MII = MF.getTarget().getInstrInfo();
+ const MRegisterInfo *RegInfo = MF.getTarget().getRegisterInfo();
+
+ while (MBB.front()->getOpcode() == TargetInstrInfo::PHI) {
+ MachineInstr *MI = MBB.front();
+ // Unlink the PHI node from the basic block... but don't delete the PHI yet
+ MBB.erase(MBB.begin());
+
+ assert(MI->getOperand(0).isVirtualRegister() &&
+ "PHI node doesn't write virt reg?");
+
+ unsigned DestReg = MI->getOperand(0).getAllocatedRegNum();
+
+ // Create a new register for the incoming PHI arguments
+ const TargetRegisterClass *RC = MF.getSSARegMap()->getRegClass(DestReg);
+ unsigned IncomingReg = MF.getSSARegMap()->createVirtualRegister(RC);
+
+ // Insert a register to register copy in the top of the current block (by
+ // after any remaining phi nodes) which copies the new incoming register
+ // into the phi node destination.
+ //
+ MachineBasicBlock::iterator AfterPHIsIt = MBB.begin();
+ while ((*AfterPHIsIt)->getOpcode() == TargetInstrInfo::PHI) ++AfterPHIsIt;
+ RegInfo->copyRegToReg(MBB, AfterPHIsIt, DestReg, IncomingReg, RC);
+
+ // Add information to LiveVariables to know that the incoming value is dead
+ if (LV) LV->addVirtualRegisterKill(IncomingReg, *(AfterPHIsIt-1));
+
+ // Now loop over all of the incoming arguments turning them into copies into
+ // the IncomingReg register in the corresponding predecessor basic block.
+ //
+ for (int i = MI->getNumOperands() - 1; i >= 2; i-=2) {
+ MachineOperand &opVal = MI->getOperand(i-1);
+
+ // Get the MachineBasicBlock equivalent of the BasicBlock that is the
+ // source path the phi
+ MachineBasicBlock &opBlock = *MI->getOperand(i).getMachineBasicBlock();
+
+ // Check to make sure we haven't already emitted the copy for this block.
+ // This can happen because PHI nodes may have multiple entries for the
+ // same basic block. It doesn't matter which entry we use though, because
+ // all incoming values are guaranteed to be the same for a particular bb.
+ //
+ // Note that this is N^2 in the number of phi node entries, but since the
+ // # of entries is tiny, this is not a problem.
+ //
+ bool HaveNotEmitted = true;
+ for (int op = MI->getNumOperands() - 1; op != i; op -= 2)
+ if (&opBlock == MI->getOperand(op).getMachineBasicBlock()) {
+ HaveNotEmitted = false;
+ break;
+ }
+
+ if (HaveNotEmitted) {
+ MachineBasicBlock::iterator I = opBlock.end()-1;
+
+ // must backtrack over ALL the branches in the previous block
+ while (MII.isTerminatorInstr((*I)->getOpcode()) && I != opBlock.begin())
+ --I;
+
+ // move back to the first branch instruction so new instructions
+ // are inserted right in front of it and not in front of a non-branch
+ if (!MII.isTerminatorInstr((*I)->getOpcode()))
+ ++I;
+
+ assert(opVal.isVirtualRegister() &&
+ "Machine PHI Operands must all be virtual registers!");
+ RegInfo->copyRegToReg(opBlock, I, IncomingReg, opVal.getReg(), RC);
+ }
+ }
+
+ // really delete the PHI instruction now!
+ delete MI;
+ }
+
+ return true;
+}