From ddaaa374879f2f736f7bfa20f4b25202fcb85708 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Mon, 23 Oct 2006 18:57:02 +0000
Subject: [PATCH] Handle fallout from the recent branch-on-undef changes.  This
 fixes Prolangs-C/agrep and SCCP/2006-10-23-IPSCCP-Crash.ll

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31132 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/SCCP.cpp | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index a55e4812df7..44634cd7c3b 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1360,7 +1360,30 @@ bool IPSCCP::runOnModule(Module &M) {
       while (!DeadBB->use_empty()) {
         Instruction *I = cast<Instruction>(DeadBB->use_back());
         bool Folded = ConstantFoldTerminator(I->getParent());
-        assert(Folded && "Didn't fold away reference to block!");
+        if (!Folded) {
+          // The constant folder may not have been able to fold the termiantor
+          // if this is a branch or switch on undef.  Fold it manually as a
+          // branch to the first successor.
+          if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
+            assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
+                   "Branch should be foldable!");
+          } else if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
+            assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
+          } else {
+            assert(0 && "Didn't fold away reference to block!");
+          }
+          
+          // Make this an uncond branch to the first successor.
+          TerminatorInst *TI = I->getParent()->getTerminator();
+          new BranchInst(TI->getSuccessor(0), TI);
+          
+          // Remove entries in successor phi nodes to remove edges.
+          for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
+            TI->getSuccessor(i)->removePredecessor(TI->getParent());
+          
+          // Remove the old terminator.
+          TI->eraseFromParent();
+        }
       }
 
       // Finally, delete the basic block.