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Don't give up on coalescing A and B when we find
A = X B = X Instead, proceed as if we had found A = X B = A git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134199 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1187,6 +1187,65 @@ static unsigned ComputeUltimateVN(VNInfo *VNI,
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return ThisValNoAssignments[VN] = UltimateVN;
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}
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// Find out if we have something like
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// A = X
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// B = X
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// if so, we can pretend this is actually
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// A = X
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// B = A
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// which allows us to coalesce A and B.
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// MI is the definition of B. LR is the life range of A that includes
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// the slot just before B. If we return true, we add "B = X" to DupCopies.
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static bool RegistersDefinedFromSameValue(const TargetRegisterInfo &tri,
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CoalescerPair &CP, MachineInstr *MI,
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LiveRange *LR,
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SmallVector<MachineInstr*, 8> &DupCopies) {
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// FIXME: This is very conservative. For example, we don't handle
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// physical registers.
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if (!MI->isFullCopy() || CP.isPartial() || CP.isPhys())
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return false;
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unsigned Dst = MI->getOperand(0).getReg();
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unsigned Src = MI->getOperand(1).getReg();
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if (!TargetRegisterInfo::isVirtualRegister(Src) ||
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!TargetRegisterInfo::isVirtualRegister(Dst))
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return false;
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unsigned A = CP.getDstReg();
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unsigned B = CP.getSrcReg();
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if (B == Dst)
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std::swap(A, B);
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assert(Dst == A);
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VNInfo *Other = LR->valno;
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if (!Other->isDefByCopy())
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return false;
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const MachineInstr *OtherMI = Other->getCopy();
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if (!OtherMI->isFullCopy())
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return false;
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unsigned OtherDst = OtherMI->getOperand(0).getReg();
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unsigned OtherSrc = OtherMI->getOperand(1).getReg();
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if (!TargetRegisterInfo::isVirtualRegister(OtherSrc) ||
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!TargetRegisterInfo::isVirtualRegister(OtherDst))
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return false;
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assert(OtherDst == B);
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if (Src != OtherSrc)
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return false;
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DupCopies.push_back(MI);
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return true;
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}
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/// JoinIntervals - Attempt to join these two intervals. On failure, this
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/// returns false.
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bool RegisterCoalescer::JoinIntervals(CoalescerPair &CP) {
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@ -1242,6 +1301,8 @@ bool RegisterCoalescer::JoinIntervals(CoalescerPair &CP) {
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DenseMap<VNInfo*, VNInfo*> RHSValsDefinedFromLHS;
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SmallVector<VNInfo*, 16> NewVNInfo;
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SmallVector<MachineInstr*, 8> DupCopies;
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LiveInterval &LHS = li_->getOrCreateInterval(CP.getDstReg());
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DEBUG({ dbgs() << "\t\tLHS = "; LHS.print(dbgs(), tri_); dbgs() << "\n"; });
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@ -1257,15 +1318,18 @@ bool RegisterCoalescer::JoinIntervals(CoalescerPair &CP) {
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if (VNI->hasRedefByEC())
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return false;
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// DstReg is known to be a register in the LHS interval. If the src is
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// from the RHS interval, we can use its value #.
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if (!CP.isCoalescable(VNI->getCopy()))
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continue;
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// Figure out the value # from the RHS.
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LiveRange *lr = RHS.getLiveRangeContaining(VNI->def.getPrevSlot());
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// The copy could be to an aliased physreg.
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if (!lr) continue;
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// DstReg is known to be a register in the LHS interval. If the src is
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// from the RHS interval, we can use its value #.
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MachineInstr *MI = VNI->getCopy();
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if (!CP.isCoalescable(MI) &&
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!RegistersDefinedFromSameValue(*tri_, CP, MI, lr, DupCopies))
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continue;
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LHSValsDefinedFromRHS[VNI] = lr->valno;
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}
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@ -1281,15 +1345,18 @@ bool RegisterCoalescer::JoinIntervals(CoalescerPair &CP) {
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if (VNI->hasRedefByEC())
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return false;
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// DstReg is known to be a register in the RHS interval. If the src is
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// from the LHS interval, we can use its value #.
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if (!CP.isCoalescable(VNI->getCopy()))
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continue;
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// Figure out the value # from the LHS.
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LiveRange *lr = LHS.getLiveRangeContaining(VNI->def.getPrevSlot());
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// The copy could be to an aliased physreg.
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if (!lr) continue;
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// DstReg is known to be a register in the RHS interval. If the src is
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// from the LHS interval, we can use its value #.
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MachineInstr *MI = VNI->getCopy();
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if (!CP.isCoalescable(MI) &&
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!RegistersDefinedFromSameValue(*tri_, CP, MI, lr, DupCopies))
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continue;
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RHSValsDefinedFromLHS[VNI] = lr->valno;
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}
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@ -1394,6 +1461,24 @@ bool RegisterCoalescer::JoinIntervals(CoalescerPair &CP) {
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if (RHSValNoAssignments.empty())
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RHSValNoAssignments.push_back(-1);
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for (SmallVector<MachineInstr*, 8>::iterator I = DupCopies.begin(),
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E = DupCopies.end(); I != E; ++I) {
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MachineInstr *MI = *I;
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// We have pretended that the assignment to B in
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// A = X
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// B = X
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// was actually a copy from A. Now that we decided to coalesce A and B,
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// transform the code into
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// A = X
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// X = X
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// and mark the X as coalesced to keep the illusion.
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unsigned Src = MI->getOperand(1).getReg();
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MI->getOperand(0).substVirtReg(Src, 0, *tri_);
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markAsJoined(MI);
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}
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// If we get here, we know that we can coalesce the live ranges. Ask the
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// intervals to coalesce themselves now.
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LHS.join(RHS, &LHSValNoAssignments[0], &RHSValNoAssignments[0], NewVNInfo,
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