Remove dead code in GVN: now that SimplifyInstruction is called

systematically, CollapsePhi will always return null here.  Note
that CollapsePhi did an extra check, isSafeReplacement, which
the SimplifyInstruction logic does not do.  I think that check
was bogus - I guess we will soon find out!  (It was originally
added in commit 41998 without a testcase).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119456 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 732f6c823cc1742161c4aeb8812877d57e6845c2..9fe77866f6fbe7baa3e9a5a2b2a431f070704dc7 100644 (file)
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -701,7 +701,6 @@ namespace {
     bool processBlock(BasicBlock *BB);
     void dump(DenseMap<uint32_t, Value*>& d);
     bool iterateOnFunction(Function &F);
-    Value *CollapsePhi(PHINode* p);
     bool performPRE(Function& F);
     Value *lookupNumber(BasicBlock *BB, uint32_t num);
     void cleanupGlobalSets();
@@ -733,33 +732,6 @@ void GVN::dump(DenseMap<uint32_t, Value*>& d) {
   errs() << "}\n";
 }
 
-static bool isSafeReplacement(PHINode* p, Instruction *inst) {
-  if (!isa<PHINode>(inst))
-    return true;
-
-  for (Instruction::use_iterator UI = p->use_begin(), E = p->use_end();
-       UI != E; ++UI)
-    if (PHINode* use_phi = dyn_cast<PHINode>(*UI))
-      if (use_phi->getParent() == inst->getParent())
-        return false;
-
-  return true;
-}
-
-Value *GVN::CollapsePhi(PHINode *PN) {
-  Value *ConstVal = PN->hasConstantValue(DT);
-  if (!ConstVal) return 0;
-
-  Instruction *Inst = dyn_cast<Instruction>(ConstVal);
-  if (!Inst)
-    return ConstVal;
-
-  if (DT->dominates(Inst, PN))
-    if (isSafeReplacement(PN, Inst))
-      return Inst;
-  return 0;
-}
-
 /// IsValueFullyAvailableInBlock - Return true if we can prove that the value
 /// we're analyzing is fully available in the specified block.  As we go, keep
 /// track of which blocks we know are fully alive in FullyAvailableBlocks.  This
@@ -1954,21 +1926,8 @@ bool GVN::processInstruction(Instruction *I,
     return false;
   }
 
-  // Collapse PHI nodes
-  if (PHINode* p = dyn_cast<PHINode>(I)) {
-    Value *constVal = CollapsePhi(p);
-
-    if (constVal) {
-      p->replaceAllUsesWith(constVal);
-      if (MD && constVal->getType()->isPointerTy())
-        MD->invalidateCachedPointerInfo(constVal);
-      VN.erase(p);
-
-      toErase.push_back(p);
-    } else {
-      localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
-    }
-
+  if (isa<PHINode>(I)) {
+    localAvail[I->getParent()]->table.insert(std::make_pair(Num, I));
   // If the number we were assigned was a brand new VN, then we don't
   // need to do a lookup to see if the number already exists
   // somewhere in the domtree: it can't!