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Be more clever about calculating live variables through new basic blocks.

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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
This commit is contained in:
Jakob Stoklund Olesen
2009-11-21 02:05:21 +00:00
parent 983c7fe847
commit 323d8c3ed7
4 changed files with 49 additions and 48 deletions
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lib/CodeGen/PHIElimination.cpp
+2 -18
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@@ -353,7 +353,7 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF,
// We break edges when registers are live out from the predecessor block
// (not considering PHI nodes). If the register is live in to this block
// anyway, we would gain nothing from splitting.
if (isLiveOut(Reg, *PreMBB, LV) && !isLiveIn(Reg, MBB, LV))
if (!LV.isLiveIn(Reg, MBB) && isLiveOut(Reg, *PreMBB, LV))
SplitCriticalEdge(PreMBB, &MBB);
}
}
@@ -406,22 +406,6 @@ bool llvm::PHIElimination::isLiveOut(unsigned Reg, const MachineBasicBlock &MBB,
return false;
}
bool llvm::PHIElimination::isLiveIn(unsigned Reg, const MachineBasicBlock &MBB,
LiveVariables &LV) {
LiveVariables::VarInfo &VI = LV.getVarInfo(Reg);
if (VI.AliveBlocks.test(MBB.getNumber()))
return true;
// defined in MBB?
const MachineInstr *Def = MRI->getVRegDef(Reg);
if (Def && Def->getParent() == &MBB)
return false;
// killed in MBB?
return VI.findKill(&MBB);
}
MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A,
MachineBasicBlock *B) {
assert(A && B && "Missing MBB end point");
@@ -463,7 +447,7 @@ MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A,
i->getOperand(ni+1).setMBB(NMBB);
if (LiveVariables *LV=getAnalysisIfAvailable<LiveVariables>())
LV->addNewBlock(NMBB, A);
LV->addNewBlock(NMBB, A, B);
if (MachineDominatorTree *MDT=getAnalysisIfAvailable<MachineDominatorTree>())
MDT->addNewBlock(NMBB, A);