[Attributor][FIX] Avoid splitting blocks if possible
Before, we eagerly split blocks even if it was not necessary, e.g., they
had a single unreachable instruction and only a single predecessor.
llvm-svn: 374703
diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 08675de..2778daf 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -2139,8 +2139,6 @@
BasicBlock *BB = I->getParent();
Instruction *SplitPos = I->getNextNode();
// TODO: mark stuff before unreachable instructions as dead.
- if (isa_and_nonnull<UnreachableInst>(SplitPos))
- continue;
if (auto *II = dyn_cast<InvokeInst>(I)) {
// If we keep the invoke the split position is at the beginning of the
@@ -2183,15 +2181,23 @@
// also manifest.
assert(!NormalDestBB->isLandingPad() &&
"Expected the normal destination not to be a landingpad!");
- BasicBlock *SplitBB =
- SplitBlockPredecessors(NormalDestBB, {BB}, ".dead");
- // The split block is live even if it contains only an unreachable
- // instruction at the end.
- assumeLive(A, *SplitBB);
- SplitPos = SplitBB->getTerminator();
+ if (NormalDestBB->getUniquePredecessor() == BB) {
+ assumeLive(A, *NormalDestBB);
+ } else {
+ BasicBlock *SplitBB =
+ SplitBlockPredecessors(NormalDestBB, {BB}, ".dead");
+ // The split block is live even if it contains only an unreachable
+ // instruction at the end.
+ assumeLive(A, *SplitBB);
+ SplitPos = SplitBB->getTerminator();
+ HasChanged = ChangeStatus::CHANGED;
+ }
}
}
+ if (isa_and_nonnull<UnreachableInst>(SplitPos))
+ continue;
+
BB = SplitPos->getParent();
SplitBlock(BB, SplitPos);
changeToUnreachable(BB->getTerminator(), /* UseLLVMTrap */ false);