Fix a bug in the unreachable block elim pass. Dropping all references on a

basic block clear()'s all of the operands lists, including phis.  This
caused removePredecessor to get confused later.  Because of this, we just
nuke (without prejudice) PHI nodes in unreachable blocks.

llvm-svn: 14635

1 files changed, 11 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/UnreachableBlockElim.cpp b/llvm/lib/CodeGen/UnreachableBlockElim.cpp
index bcc124538d3..1b59ac4a666 100644
--- a/llvm/lib/CodeGen/UnreachableBlockElim.cpp
+++ b/llvm/lib/CodeGen/UnreachableBlockElim.cpp
@@ -21,6 +21,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/Passes.h"
+#include "llvm/iPHINode.h"
+#include "llvm/Constant.h"
 #include "llvm/Function.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/CFG.h"
@@ -52,10 +54,15 @@ bool UnreachableBlockElim::runOnFunction(Function &F) {
   std::vector<BasicBlock*> DeadBlocks;
   for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
     if (!Reachable.count(I)) {
-      DeadBlocks.push_back(I);
-      for (succ_iterator SI = succ_begin(&*I), E = succ_end(&*I); SI != E; ++SI)
-        (*SI)->removePredecessor(I);
-      I->dropAllReferences();
+      BasicBlock *BB = I;
+      DeadBlocks.push_back(BB);
+      while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
+        PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
+        BB->getInstList().pop_front();
+      }
+      for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
+        (*SI)->removePredecessor(BB);
+      BB->dropAllReferences();
     }
 
   if (DeadBlocks.empty()) return false;