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Throttle tail merging; handling blocks with large numbers of predecessors

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is too slow.

llvm-svn: 37509
This commit is contained in:
Dale Johannesen 2007-06-08 00:34:27 +00:00
parent 738f460b18
commit 0903dd4e52
1 changed files with 6 additions and 2 deletions
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8
lib/CodeGen/BranchFolding.cpp
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@ -564,6 +564,9 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
return MadeChange;
}
// Throttle for huge numbers of predecessors (compile speed problems)
#define THRESHOLD 100
bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
if (!EnableTailMerge) return false;
@ -577,7 +580,8 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
MergePotentials.push_back(std::make_pair(HashEndOfMBB(I, 2U), I));
}
// See if we can do any tail merging on those.
MadeChange |= TryMergeBlocks(NULL, NULL);
if (MergePotentials.size() < THRESHOLD)
MadeChange |= TryMergeBlocks(NULL, NULL);
// Look at blocks (IBB) with multiple predecessors (PBB).
// We change each predecessor to a canonical form, by
@ -599,7 +603,7 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
// transformations.)
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
if (!I->succ_empty() && I->pred_size() >= 2) {
if (!I->succ_empty() && I->pred_size() >= 2 && I->pred_size() < THRESHOLD) {
MachineBasicBlock *IBB = I;
MachineBasicBlock *PredBB = prior(I);
MergePotentials.clear();