From 7af7b1c82c196276807365348c1d3113168cbda4 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Thu, 23 Jan 2003 02:12:18 +0000
Subject: [PATCH] Fix bug: ADCE/2003-01-22-PredecessorProblem.ll

llvm-svn: 5405
---
 lib/Transforms/Scalar/ADCE.cpp | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/lib/Transforms/Scalar/ADCE.cpp b/lib/Transforms/Scalar/ADCE.cpp
index e2e9e86216c..24ccee60344 100644
--- a/lib/Transforms/Scalar/ADCE.cpp
+++ b/lib/Transforms/Scalar/ADCE.cpp
@@ -331,10 +331,17 @@ bool ADCE::doADCE() {
       }
   }
 
-  // Loop over all of the basic blocks in the function, dropping references of
-  // the dead basic blocks
+  // We make changes if there are any dead blocks in the function...
+  if (unsigned NumDeadBlocks = Func->size() - AliveBlocks.size()) {
+    MadeChanges = true;
+    NumBlockRemoved += NumDeadBlocks;
+  }
+
+  // Loop over all of the basic blocks in the function, removing control flow
+  // edges to live blocks (also eliminating any entries in PHI functions in
+  // referenced blocks).
   //
-  for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB) {
+  for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB)
     if (!AliveBlocks.count(BB)) {
       // Remove all outgoing edges from this basic block and convert the
       // terminator into a return instruction.
@@ -354,12 +361,16 @@ bool ADCE::doADCE() {
         BB->getInstList().push_back(new ReturnInst(RetTy != Type::VoidTy ?
                                            Constant::getNullValue(RetTy) : 0));
       }
-
-      BB->dropAllReferences();
-      ++NumBlockRemoved;
-      MadeChanges = true;
     }
-  }
+
+
+  // Loop over all of the basic blocks in the function, dropping references of
+  // the dead basic blocks.  We must do this after the previous step to avoid
+  // dropping references to PHIs which still have entries...
+  //
+  for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB)
+    if (!AliveBlocks.count(BB))
+      BB->dropAllReferences();
 
   // Now loop through all of the blocks and delete the dead ones.  We can safely
   // do this now because we know that there are no references to dead blocks