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Teach the jump threading optimization to stop scanning the basic block when calculating the cost after passing the threshold. 

llvm-svn: 169135
This commit is contained in:
Nadav Rotem 2012-12-03 17:34:44 +00:00
parent 4c2094be3c
commit 2349531def
1 changed files with 10 additions and 5 deletions
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15
llvm/lib/Transforms/Scalar/JumpThreading.cpp
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@ -216,19 +216,24 @@ bool JumpThreading::runOnFunction(Function &F) {
}
/// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
/// thread across it.
static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
/// thread across it. Stop scanning the block when passing the threshold.
static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB,
unsigned Threshold) {
/// Ignore PHI nodes, these will be flattened when duplication happens.
BasicBlock::const_iterator I = BB->getFirstNonPHI();
// FIXME: THREADING will delete values that are just used to compute the
// branch, so they shouldn't count against the duplication cost.
// Sum up the cost of each instruction until we get to the terminator. Don't
// include the terminator because the copy won't include it.
unsigned Size = 0;
for (; !isa<TerminatorInst>(I); ++I) {
// Stop scanning the block if we've reached the threshold.
if (Size > Threshold)
return Size;
// Debugger intrinsics don't incur code size.
if (isa<DbgInfoIntrinsic>(I)) continue;
@ -1337,7 +1342,7 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB,
return false;
}
unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB, Threshold);
if (JumpThreadCost > Threshold) {
DEBUG(dbgs() << " Not threading BB '" << BB->getName()
<< "' - Cost is too high: " << JumpThreadCost << "\n");
@ -1481,7 +1486,7 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
return false;
}
unsigned DuplicationCost = getJumpThreadDuplicationCost(BB);
unsigned DuplicationCost = getJumpThreadDuplicationCost(BB, Threshold);
if (DuplicationCost > Threshold) {
DEBUG(dbgs() << " Not duplicating BB '" << BB->getName()
<< "' - Cost is too high: " << DuplicationCost << "\n");