Fix LCSSA to avoid emitting a PHI node for the unwind destination of

an invoke instruction, since the value isn't really live across that
edge.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74242 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 11 insertions, 2 deletions

diff --git a/lib/Transforms/Utils/LCSSA.cpp b/lib/Transforms/Utils/LCSSA.cpp
index 7d4f3a343e..d5e7303a50 100644
--- a/lib/Transforms/Utils/LCSSA.cpp
+++ b/lib/Transforms/Utils/LCSSA.cpp
@@ -149,7 +149,16 @@ void LCSSA::ProcessInstruction(Instruction *Instr,
   // Keep track of the blocks that have the value available already.
   DenseMap<DomTreeNode*, Value*> Phis;
 
-  DomTreeNode *InstrNode = DT->getNode(Instr->getParent());
+  BasicBlock *DomBB = Instr->getParent();
+
+  // Invoke instructions are special in that their result value is not available
+  // along their unwind edge. The code below tests to see whether DomBB dominates
+  // the value, so adjust DomBB to the normal destination block, which is
+  // effectively where the value is first usable.
+  if (InvokeInst *Inv = dyn_cast<InvokeInst>(Instr))
+    DomBB = Inv->getNormalDest();
+
+  DomTreeNode *DomNode = DT->getNode(DomBB);
 
   // Insert the LCSSA phi's into the exit blocks (dominated by the value), and
   // add them to the Phi's map.
@@ -158,7 +167,7 @@ void LCSSA::ProcessInstruction(Instruction *Instr,
     BasicBlock *BB = *BBI;
     DomTreeNode *ExitBBNode = DT->getNode(BB);
     Value *&Phi = Phis[ExitBBNode];
-    if (!Phi && DT->dominates(InstrNode, ExitBBNode)) {
+    if (!Phi && DT->dominates(DomNode, ExitBBNode)) {
       PHINode *PN = PHINode::Create(Instr->getType(), Instr->getName()+".lcssa",
                                     BB->begin());
       PN->reserveOperandSpace(PredCache.GetNumPreds(BB));