Make tail merging handle blocks with repeated predecessors correctly, and
remove RemoveDuplicateSuccessor, as it is no longer necessary, and because
it breaks assumptions made in
MachineBasicBlock::isOnlyReachableByFallthrough.
Convert test/CodeGen/X86/omit-label.ll to FileCheck and add a testcase
for PR4732.
test/CodeGen/Thumb2/thumb2-ifcvt2.ll sees a diff with this commit due to
it being bugpoint-reduced to the point where it doesn't matter what the
condition for the branch is.
Add some more interesting code to
test/CodeGen/X86/2009-08-06-branchfolder-crash.ll, which is the testcase
that originally motivated the RemoveDuplicateSuccessor code, to help
verify that the original problem isn't being re-broken.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79338 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 1ab3df2..1ce83f8 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -700,6 +700,7 @@
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) {
+ SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
MachineBasicBlock *IBB = I;
MachineBasicBlock *PredBB = prior(I);
MergePotentials.clear();
@@ -710,6 +711,9 @@
// Skip blocks that loop to themselves, can't tail merge these.
if (PBB==IBB)
continue;
+ // Visit each predecessor only once.
+ if (!UniquePreds.insert(PBB))
+ continue;
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond, true)) {
@@ -850,27 +854,6 @@
return CanFallThrough(CurBB, CurUnAnalyzable, TBB, FBB, Cond);
}
-/// RemoveDuplicateSuccessor - make sure block Pred has at most one
-/// successor edge leading to Succ. This is only called in one place,
-/// but Chris prefers that it be a separate function.
-static void RemoveDuplicateSuccessor(MachineBasicBlock *Pred,
- MachineBasicBlock *Succ) {
- MachineBasicBlock::succ_iterator SI = Pred->succ_begin();
- bool found = false;
- while (SI != Pred->succ_end()) {
- if (*SI == Succ) {
- if (!found) {
- found = true;
- ++SI;
- } else {
- SI = Pred->removeSuccessor(SI);
- }
- } else {
- ++SI;
- }
- }
-}
-
/// IsBetterFallthrough - Return true if it would be clearly better to
/// fall-through to MBB1 than to fall through into MBB2. This has to return
/// a strict ordering, returning true for both (MBB1,MBB2) and (MBB2,MBB1) will
@@ -914,10 +897,6 @@
while (!MBB->pred_empty()) {
MachineBasicBlock *Pred = *(MBB->pred_end()-1);
Pred->ReplaceUsesOfBlockWith(MBB, FallThrough);
- // If this resulted in a predecessor with true and false edges
- // both going to the fallthrough block, clean up;
- // BranchFolding doesn't like this.
- RemoveDuplicateSuccessor(Pred, FallThrough);
}
// If MBB was the target of a jump table, update jump tables to go to the
// fallthrough instead.