From c6694228fa8df57193cbd924d627814384106ba2 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sun, 9 Mar 2008 05:04:48 +0000
Subject: [PATCH] Two things. Preserve the unwind_to when splitting a BB. Add
 the ability to remove just one instance of a BB from a phi node. This fixes
 the compile error in the tree now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48085 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/BasicBlock.h                |  6 +++++-
 lib/Transforms/Utils/BasicBlockUtils.cpp |  1 +
 lib/VMCore/BasicBlock.cpp                | 19 +++++++++++++------
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/include/llvm/BasicBlock.h b/include/llvm/BasicBlock.h
index 4099d3bd32e..253a8fa1a06 100644
--- a/include/llvm/BasicBlock.h
+++ b/include/llvm/BasicBlock.h
@@ -185,7 +185,11 @@ public:
   /// DontDeleteUselessPHIs will keep PHIs that have one value or the same 
   /// value for all entries.
   ///
-  void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false);
+  /// OnlyDeleteOne will only remove one entry from a PHI, in case there were
+  /// duplicate entries for the Pred.
+  ///
+  void removePredecessor(BasicBlock *Pred, bool DontDeleteUselessPHIs = false,
+                         bool OnlyDeleteOne = false);
 
   /// splitBasicBlock - This splits a basic block into two at the specified
   /// instruction.  Note that all instructions BEFORE the specified iterator
diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 3607237e41d..0dc38a2b84a 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -160,6 +160,7 @@ BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
   while (isa<PHINode>(SplitIt))
     ++SplitIt;
   BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
+  New->setUnwindDest(Old->getUnwindDest());
 
   // The new block lives in whichever loop the old one did.
   if (Loop *L = LI.getLoopFor(Old))
diff --git a/lib/VMCore/BasicBlock.cpp b/lib/VMCore/BasicBlock.cpp
index f9bead74d25..1288fdf32c4 100644
--- a/lib/VMCore/BasicBlock.cpp
+++ b/lib/VMCore/BasicBlock.cpp
@@ -188,14 +188,12 @@ BasicBlock *BasicBlock::getSinglePredecessor() {
 /// called while the predecessor still refers to this block.
 ///
 void BasicBlock::removePredecessor(BasicBlock *Pred,
-                                   bool DontDeleteUselessPHIs) {
+                                   bool DontDeleteUselessPHIs,
+                                   bool OnlyDeleteOne) {
   assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
           find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
          "removePredecessor: BB is not a predecessor!");
 
-  if (Pred == getUnwindDest())
-    setUnwindDest(NULL);
-
   if (InstList.empty()) return;
   PHINode *APN = dyn_cast<PHINode>(&front());
   if (!APN) return;   // Quick exit.
@@ -226,7 +224,11 @@ void BasicBlock::removePredecessor(BasicBlock *Pred,
     // Yup, loop through and nuke the PHI nodes
     while (PHINode *PN = dyn_cast<PHINode>(&front())) {
       // Remove the predecessor first.
-      PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
+      if (OnlyDeleteOne) {
+        int idx = PN->getBasicBlockIndex(Pred);
+        PN->removeIncomingValue(idx, !DontDeleteUselessPHIs);
+      } else
+        PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
 
       // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
       if (max_idx == 2) {
@@ -247,7 +249,12 @@ void BasicBlock::removePredecessor(BasicBlock *Pred,
     PHINode *PN;
     for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
       ++II;
-      PN->removeIncomingValue(Pred, false);
+      if (OnlyDeleteOne) {
+        int idx = PN->getBasicBlockIndex(Pred);
+        PN->removeIncomingValue(idx, false);
+      } else 
+        PN->removeIncomingValue(Pred, false);
+
       // If all incoming values to the Phi are the same, we can replace the Phi
       // with that value.
       Value* PNV = 0;