Move EliminateDuplicatePHINodes() from SimplifyCFG.cpp to Local.cpp
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90324 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index aef0f5f..7a37aa3 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -603,3 +603,65 @@
return true;
}
+/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
+/// nodes in this block. This doesn't try to be clever about PHI nodes
+/// which differ only in the order of the incoming values, but instcombine
+/// orders them so it usually won't matter.
+///
+bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
+ bool Changed = false;
+
+ // This implementation doesn't currently consider undef operands
+ // specially. Theroetically, two phis which are identical except for
+ // one having an undef where the other doesn't could be collapsed.
+
+ // Map from PHI hash values to PHI nodes. If multiple PHIs have
+ // the same hash value, the element is the first PHI in the
+ // linked list in CollisionMap.
+ DenseMap<uintptr_t, PHINode *> HashMap;
+
+ // Maintain linked lists of PHI nodes with common hash values.
+ DenseMap<PHINode *, PHINode *> CollisionMap;
+
+ // Examine each PHI.
+ for (BasicBlock::iterator I = BB->begin();
+ PHINode *PN = dyn_cast<PHINode>(I++); ) {
+ // Compute a hash value on the operands. Instcombine will likely have sorted
+ // them, which helps expose duplicates, but we have to check all the
+ // operands to be safe in case instcombine hasn't run.
+ uintptr_t Hash = 0;
+ for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
+ // This hash algorithm is quite weak as hash functions go, but it seems
+ // to do a good enough job for this particular purpose, and is very quick.
+ Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
+ Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
+ }
+ // If we've never seen this hash value before, it's a unique PHI.
+ std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
+ HashMap.insert(std::make_pair(Hash, PN));
+ if (Pair.second) continue;
+ // Otherwise it's either a duplicate or a hash collision.
+ for (PHINode *OtherPN = Pair.first->second; ; ) {
+ if (OtherPN->isIdenticalTo(PN)) {
+ // A duplicate. Replace this PHI with its duplicate.
+ PN->replaceAllUsesWith(OtherPN);
+ PN->eraseFromParent();
+ Changed = true;
+ break;
+ }
+ // A non-duplicate hash collision.
+ DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
+ if (I == CollisionMap.end()) {
+ // Set this PHI to be the head of the linked list of colliding PHIs.
+ PHINode *Old = Pair.first->second;
+ Pair.first->second = PN;
+ CollisionMap[PN] = Old;
+ break;
+ }
+ // Procede to the next PHI in the list.
+ OtherPN = I->second;
+ }
+ }
+
+ return Changed;
+}