Make jump threading eliminate blocks that just contain phi nodes,
debug intrinsics, and an unconditional branch when possible. This
reuses the TryToSimplifyUncondBranchFromEmptyBlock function split
out of simplifycfg.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86722 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 9c9461fa..1d89399 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -115,6 +115,7 @@
bool Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
BasicBlock *BB = I;
+ // Thread all of the branches we can over this block.
while (ProcessBlock(BB))
Changed = true;
@@ -129,6 +130,26 @@
LoopHeaders.erase(BB);
DeleteDeadBlock(BB);
Changed = true;
+ } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
+ // Can't thread an unconditional jump, but if the block is "almost
+ // empty", we can replace uses of it with uses of the successor and make
+ // this dead.
+ if (BI->isUnconditional() &&
+ BB != &BB->getParent()->getEntryBlock()) {
+ BasicBlock::iterator BBI = BB->getFirstNonPHI();
+ // Ignore dbg intrinsics.
+ while (isa<DbgInfoIntrinsic>(BBI))
+ ++BBI;
+ // If the terminator is the only non-phi instruction, try to nuke it.
+ if (BBI->isTerminator()) {
+ bool Erased = LoopHeaders.erase(BB);
+
+ if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
+ Changed = true;
+ else if (Erased)
+ LoopHeaders.insert(BB);
+ }
+ }
}
}
AnotherIteration = Changed;