Simplify the logic of getting hold of a PHI predecessor block.
There is now a direct way from value-use-iterator to incoming block in PHINode's API.
This way we avoid the iterator->index->iterator trip, and especially the costly
getOperandNo() invocation. Additionally there is now an assertion that the iterator
really refers to one of the PHI's Uses.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62869 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/LCSSA.cpp b/lib/Transforms/Utils/LCSSA.cpp
index 3855888..9cd7e69 100644
--- a/lib/Transforms/Utils/LCSSA.cpp
+++ b/lib/Transforms/Utils/LCSSA.cpp
@@ -175,8 +175,7 @@
        UI != E;) {
     BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
     if (PHINode *P = dyn_cast<PHINode>(*UI)) {
-      unsigned OperandNo = UI.getOperandNo();
-      UserBB = P->getIncomingBlock(OperandNo/2);
+      UserBB = P->getIncomingBlock(UI);
     }
     
     // If the user is in the loop, don't rewrite it!
@@ -212,8 +211,7 @@
            ++UI) {
         BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
         if (PHINode* p = dyn_cast<PHINode>(*UI)) {
-          unsigned OperandNo = UI.getOperandNo();
-          UserBB = p->getIncomingBlock(OperandNo/2);
+          UserBB = p->getIncomingBlock(UI);
         }
         
         if (*BB != UserBB && !inLoop(UserBB)) {