Be more clever about calculating live variables through new basic blocks.
When splitting a critical edge, the registers live through the edge are:
- Used in a PHI instruction, or
- Live out from the predecessor, and
- Live in to the successor.
This allows the coalescer to eliminate even more phi joins.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89530 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveVariables.cpp b/lib/CodeGen/LiveVariables.cpp
index 16a79bb..bfc2d08 100644
--- a/lib/CodeGen/LiveVariables.cpp
+++ b/lib/CodeGen/LiveVariables.cpp
@@ -656,35 +656,45 @@
.push_back(BBI->getOperand(i).getReg());
}
+bool LiveVariables::VarInfo::isLiveIn(const MachineBasicBlock &MBB,
+ unsigned Reg,
+ MachineRegisterInfo &MRI) {
+ unsigned Num = MBB.getNumber();
+
+ // Reg is live-through.
+ if (AliveBlocks.test(Num))
+ return true;
+
+ // Registers defined in MBB cannot be live in.
+ const MachineInstr *Def = MRI.getVRegDef(Reg);
+ if (Def && Def->getParent() == &MBB)
+ return false;
+
+ // Reg was not defined in MBB, was it killed here?
+ return findKill(&MBB);
+}
+
/// addNewBlock - Add a new basic block BB as an empty succcessor to DomBB. All
/// variables that are live out of DomBB will be marked as passing live through
/// BB.
void LiveVariables::addNewBlock(MachineBasicBlock *BB,
- MachineBasicBlock *DomBB) {
+ MachineBasicBlock *DomBB,
+ MachineBasicBlock *SuccBB) {
const unsigned NumNew = BB->getNumber();
- const unsigned NumDom = DomBB->getNumber();
+
+ // All registers used by PHI nodes in SuccBB must be live through BB.
+ for (MachineBasicBlock::const_iterator BBI = SuccBB->begin(),
+ BBE = SuccBB->end();
+ BBI != BBE && BBI->getOpcode() == TargetInstrInfo::PHI; ++BBI)
+ for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
+ if (BBI->getOperand(i+1).getMBB() == BB)
+ getVarInfo(BBI->getOperand(i).getReg()).AliveBlocks.set(NumNew);
// Update info for all live variables
for (unsigned Reg = TargetRegisterInfo::FirstVirtualRegister,
E = MRI->getLastVirtReg()+1; Reg != E; ++Reg) {
VarInfo &VI = getVarInfo(Reg);
-
- // Anything live through DomBB is also live through BB.
- if (VI.AliveBlocks.test(NumDom)) {
+ if (!VI.AliveBlocks.test(NumNew) && VI.isLiveIn(*SuccBB, Reg, *MRI))
VI.AliveBlocks.set(NumNew);
- continue;
- }
-
- // Variables not defined in DomBB cannot be live out.
- const MachineInstr *Def = MRI->getVRegDef(Reg);
- if (!Def || Def->getParent() != DomBB)
- continue;
-
- // Killed by DomBB?
- if (VI.findKill(DomBB))
- continue;
-
- // This register is defined in DomBB and live out
- VI.AliveBlocks.set(NumNew);
}
}