Throttle tail merging; handling blocks with large numbers of predecessors
is too slow.
llvm-svn: 37509
diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index ffde173..1125511 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -564,6 +564,9 @@
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 @@
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 @@
// 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();