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Split *all* critical edges before isel. This resolves issues with spill code 

being inserted on unsplit critical edges, which introduces (sometimes large
amounts of) partially dead spill code.

This also fixes PR925 + CodeGen/Generic/switch-crit-edge-constant.ll

llvm-svn: 31260
This commit is contained in:
Chris Lattner 2006-10-28 17:04:37 +00:00
parent 5217111abe
commit 3e6b1c6157
1 changed files with 8 additions and 44 deletions
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52
llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
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@ -3490,64 +3490,28 @@ static bool OptimizeGEPExpression(GetElementPtrInst *GEPI,
return true;
}
/// SplitCritEdgesForPHIConstants - If this block has any PHI nodes with
/// constant operands, and if any of the edges feeding the PHI node are
/// critical, split them so that the assignments of a constant to a register
/// will not be executed on a path that isn't relevant.
void SelectionDAGISel::SplitCritEdgesForPHIConstants(BasicBlock *BB) {
// The most common case is that this is a PHI node with two incoming
// successors handle this case efficiently, because it is simple.
PHINode *PN = cast<PHINode>(BB->begin());
if (PN->getNumIncomingValues() == 2) {
// If neither edge is critical, we never need to split.
if (PN->getIncomingBlock(0)->getTerminator()->getNumSuccessors() == 1 &&
PN->getIncomingBlock(1)->getTerminator()->getNumSuccessors() == 1)
return;
BasicBlock::iterator BBI = BB->begin();
while ((PN = dyn_cast<PHINode>(BBI++))) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (isa<Constant>(PN->getIncomingValue(i)))
SplitCriticalEdge(PN->getIncomingBlock(i), BB);
}
return;
}
// Otherwise, things are a bit trickier.
// BE SMART HERE.
BasicBlock::iterator BBI = BB->begin();
while ((PN = dyn_cast<PHINode>(BBI++))) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (isa<Constant>(PN->getIncomingValue(i)))
SplitCriticalEdge(PN->getIncomingBlock(i), BB);
}
}
bool SelectionDAGISel::runOnFunction(Function &Fn) {
MachineFunction &MF = MachineFunction::construct(&Fn, TLI.getTargetMachine());
RegMap = MF.getSSARegMap();
DEBUG(std::cerr << "\n\n\n=== " << Fn.getName() << "\n");
// First, split all critical edges for PHI nodes with incoming values that are
// constants, this way the load of the constant into a vreg will not be placed
// into MBBs that are used some other way.
// First, split all critical edges.
//
// In this pass we also look for GEP and cast instructions that are used
// across basic blocks and rewrite them to improve basic-block-at-a-time
// selection.
//
//
bool MadeChange = true;
while (MadeChange) {
MadeChange = false;
for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
// If this block has any PHI nodes with constant operands, and if any of the
// edges feeding the PHI node are critical, split them.
if (isa<PHINode>(BB->begin()))
SplitCritEdgesForPHIConstants(BB);
// Split all critical edges.
TerminatorInst *BBTI = BB->getTerminator();
if (BBTI->getNumSuccessors() > 1) {
for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i)
SplitCriticalEdge(BBTI, i, this, true);
}
for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ) {
Instruction *I = BBI++;