6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-06-13 04:38:24 +00:00
Code Issues Projects Releases Wiki Activity

Make the threshold used by branch folding softer. Before we would get a

Browse Source 
sharp all or nothing transition when one extra predecessor was added. Now
we still test first ones for merging.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132974 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2011-06-14 04:41:17 +00:00
parent 3c2f0a11cc
commit 3a42565ccb
3 changed files with 64 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
lib/CodeGen/BranchFolding.cpp
View File

@ -799,14 +799,22 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
// First find blocks with no successors.
MergePotentials.clear();
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
for (MachineFunction::iterator I = MF.begin(), E = MF.end();
I != E && MergePotentials.size() < TailMergeThreshold; ++I) {
if (TriedMerging.count(I))
continue;
if (I->succ_empty())
MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I), I));
}
// If this is a large problem, avoid visiting the same basic blocks
// multiple times.
if (MergePotentials.size() == TailMergeThreshold)
for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
TriedMerging.insert(MergePotentials[i].getBlock());
// See if we can do any tail merging on those.
if (MergePotentials.size() < TailMergeThreshold &&
MergePotentials.size() >= 2)
if (MergePotentials.size() >= 2)
MadeChange |= TryTailMergeBlocks(NULL, NULL);
// Look at blocks (IBB) with multiple predecessors (PBB).
@ -830,15 +838,17 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end();
I != E; ++I) {
if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) {
if (I->pred_size() >= 2) {
SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
MachineBasicBlock *IBB = I;
MachineBasicBlock *PredBB = prior(I);
MergePotentials.clear();
for (MachineBasicBlock::pred_iterator P = I->pred_begin(),
E2 = I->pred_end();
P != E2; ++P) {
P != E2 && MergePotentials.size() < TailMergeThreshold; ++P) {
MachineBasicBlock *PBB = *P;
if (TriedMerging.count(PBB))
continue;
// Skip blocks that loop to themselves, can't tail merge these.
if (PBB == IBB)
continue;
@ -891,6 +901,12 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB), *P));
}
}
// If this is a large problem, avoid visiting the same basic blocks
// multiple times.
if (MergePotentials.size() == TailMergeThreshold)
for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
TriedMerging.insert(MergePotentials[i].getBlock());
if (MergePotentials.size() >= 2)
MadeChange |= TryTailMergeBlocks(IBB, PredBB);
// Reinsert an unconditional branch if needed.