STATISTIC(NumTailMerge , "Number of block tails merged");
static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
cl::init(cl::BOU_UNSET), cl::Hidden);
-namespace {
- // Throttle for huge numbers of predecessors (compile speed problems)
- static cl::opt<unsigned>
- TailMergeThreshold("tail-merge-threshold",
- cl::desc("Max number of predecessors to consider tail merging"),
- cl::init(100), cl::Hidden);
+// Throttle for huge numbers of predecessors (compile speed problems)
+static cl::opt<unsigned>
+TailMergeThreshold("tail-merge-threshold",
+ cl::desc("Max number of predecessors to consider tail merging"),
+ cl::init(100), cl::Hidden);
+namespace {
struct VISIBILITY_HIDDEN BranchFolder : public MachineFunctionPass {
static char ID;
explicit BranchFolder(bool defaultEnableTailMerge) :
CurMPIter->second,
I->second,
TrialBBI1, TrialBBI2);
- if (CommonTailLen >= minCommonTailLength) {
+ // If we will have to split a block, there should be at least
+ // minCommonTailLength instructions in common; if not, at worst
+ // we will be replacing a fallthrough into the common tail with a
+ // branch, which at worst breaks even with falling through into
+ // the duplicated common tail, so 1 instruction in common is enough.
+ // We will always pick a block we do not have to split as the common
+ // tail if there is one.
+ // (Empty blocks will get forwarded and need not be considered.)
+ if (CommonTailLen >= minCommonTailLength ||
+ (CommonTailLen > 0 &&
+ (TrialBBI1==CurMPIter->second->begin() ||
+ TrialBBI2==I->second->begin()))) {
if (CommonTailLen > maxCommonTailLength) {
SameTails.clear();
maxCommonTailLength = CommonTailLen;
void BranchFolder::RemoveBlocksWithHash(unsigned CurHash,
MachineBasicBlock* SuccBB,
MachineBasicBlock* PredBB) {
- for (MPIterator CurMPIter = prior(MergePotentials.end()),
- B = MergePotentials.begin();
+ MPIterator CurMPIter, B;
+ for (CurMPIter = prior(MergePotentials.end()), B = MergePotentials.begin();
CurMPIter->first==CurHash;
--CurMPIter) {
// Put the unconditional branch back, if we need one.
MachineBasicBlock *CurMBB = CurMPIter->second;
if (SuccBB && CurMBB != PredBB)
FixTail(CurMBB, SuccBB, TII);
- MergePotentials.erase(CurMPIter);
- if (CurMPIter==B)
+ if (CurMPIter==B)
break;
}
+ if (CurMPIter->first!=CurHash)
+ CurMPIter++;
+ MergePotentials.erase(CurMPIter, MergePotentials.end());
}
/// CreateCommonTailOnlyBlock - None of the blocks to be tail-merged consist