[Constant Hoisting] Fix insertion point for constant materialization.

The bitcast instruction during constant materialization was not placed correcly
in the presence of phi nodes. This commit fixes the insertion point to be in the
idom instead.

This fixes PR18768

llvm-svn: 201009

1 files changed, 21 insertions, 18 deletions

diff --git a/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp b/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
index 28a31a97025..0fca617be7e 100644
--- a/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstantHoisting.cpp
@@ -148,6 +148,8 @@ void ConstantHoisting::CollectConstant(User * U, unsigned Opcode,
     ConstantCandidate &CC = ConstantMap[C];
     CC.CumulativeCost += Cost;
     CC.Uses.push_back(U);
+    DEBUG(dbgs() << "Collect constant " << *C << " with cost " << Cost
+                 << " from " << *U << '\n');
   }
 }
 
@@ -279,6 +281,20 @@ static void CollectBasicBlocks(SmallPtrSet<BasicBlock *, 4> &BBs, Function &F,
           BBs.insert(I->getParent());
 }
 
+/// \brief Find the instruction we should insert the constant materialization
+/// before.
+static Instruction *getMatInsertPt(Instruction *I, const DominatorTree *DT) {
+  if (!isa<PHINode>(I) && !isa<LandingPadInst>(I)) // Simple case.
+    return I;
+
+  // We can't insert directly before a phi node or landing pad. Insert before
+  // the terminator of the dominating block.
+  assert(&I->getParent()->getParent()->getEntryBlock() != I->getParent() &&
+         "PHI or landing pad in entry block!");
+  BasicBlock *IDom = DT->getNode(I->getParent())->getIDom()->getBlock();
+  return IDom->getTerminator();
+}
+
 /// \brief Find an insertion point that dominates all uses.
 Instruction *ConstantHoisting::
 FindConstantInsertionPoint(Function &F, const ConstantInfo &CI) const {
@@ -291,10 +307,10 @@ FindConstantInsertionPoint(Function &F, const ConstantInfo &CI) const {
        RCI != RCE; ++RCI)
     for (SmallVectorImpl<User *>::const_iterator U = RCI->Uses.begin(),
          E = RCI->Uses.end(); U != E; ++U)
-        CollectBasicBlocks(BBs, F, *U);
+      CollectBasicBlocks(BBs, F, *U);
 
   if (BBs.count(Entry))
-    return Entry->getFirstInsertionPt();
+    return getMatInsertPt(&Entry->front(), DT);
 
   while (BBs.size() >= 2) {
     BasicBlock *BB, *BB1, *BB2;
@@ -302,27 +318,14 @@ FindConstantInsertionPoint(Function &F, const ConstantInfo &CI) const {
     BB2 = *llvm::next(BBs.begin());
     BB = DT->findNearestCommonDominator(BB1, BB2);
     if (BB == Entry)
-      return Entry->getFirstInsertionPt();
+      return getMatInsertPt(&Entry->front(), DT);
     BBs.erase(BB1);
     BBs.erase(BB2);
     BBs.insert(BB);
   }
   assert((BBs.size() == 1) && "Expected only one element.");
-  return (*BBs.begin())->getFirstInsertionPt();
-}
-
-/// \brief Find the instruction we should insert the constant materialization
-/// before.
-static Instruction *getMatInsertPt(Instruction *I, const DominatorTree *DT) {
-  if (!isa<PHINode>(I) && !isa<LandingPadInst>(I)) // Simple case.
-    return I;
-
-  // We can't insert directly before a phi node or landing pad. Insert before
-  // the terminator of the dominating block.
-  assert(&I->getParent()->getParent()->getEntryBlock() != I->getParent() &&
-         "PHI or landing pad in entry block!");
-  BasicBlock *IDom = DT->getNode(I->getParent())->getIDom()->getBlock();
-  return IDom->getTerminator();
+  Instruction &FirstInst = (*BBs.begin())->front();
+  return getMatInsertPt(&FirstInst, DT);
 }
 
 /// \brief Emit materialization code for all rebased constants and update their