From 5f28475b30cf09e946bf6cb7c8de6d597a41610e Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Sun, 24 Oct 2010 12:23:30 +0000
Subject: [PATCH] Fix PR8445: a block with no predecessors may be the entry
 block, in which case it isn't unreachable and should not be zapped.  The
 check for the entry block was missing in one case: a block containing a
 unwind instruction.  While there, do some small cleanups: "M" is not a great
 name for a Function* (it would be more appropriate for a Module*), change it
 to "Fn"; use Fn in more places.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117224 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyCFG.cpp          | 22 +++++++++----------
 .../2010-10-24-OnlyUnwindInEntry.ll           |  6 +++++
 2 files changed, 16 insertions(+), 12 deletions(-)
 create mode 100644 test/Transforms/SimplifyCFG/2010-10-24-OnlyUnwindInEntry.ll

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 28d7afbf1c3..de1f12ec1b7 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1720,15 +1720,14 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
 
 bool SimplifyCFGOpt::run(BasicBlock *BB) {
   bool Changed = false;
-  Function *M = BB->getParent();
+  Function *Fn = BB->getParent();
 
-  assert(BB && BB->getParent() && "Block not embedded in function!");
+  assert(BB && Fn && "Block not embedded in function!");
   assert(BB->getTerminator() && "Degenerate basic block encountered!");
 
   // Remove basic blocks that have no predecessors (except the entry block)...
   // or that just have themself as a predecessor.  These are unreachable.
-  if ((pred_begin(BB) == pred_end(BB) &&
-       &BB->getParent()->getEntryBlock() != BB) ||
+  if ((pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) ||
       BB->getSinglePredecessor() == BB) {
     DEBUG(dbgs() << "Removing BB: \n" << *BB);
     DeleteDeadBlock(BB);
@@ -1798,7 +1797,7 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
         // If we eliminated all predecessors of the block, delete the block now.
         if (pred_begin(BB) == pred_end(BB))
           // We know there are no successors, so just nuke the block.
-          M->getBasicBlockList().erase(BB);
+          Fn->getBasicBlockList().erase(BB);
 
         return true;
       }
@@ -1847,10 +1846,10 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
       Preds.pop_back();
     }
 
-    // If this block is now dead, remove it.
-    if (pred_begin(BB) == pred_end(BB)) {
+    // If this block is now dead (and isn't the entry block), remove it.
+    if (pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) {
       // We know there are no successors, so just nuke the block.
-      M->getBasicBlockList().erase(BB);
+      Fn->getBasicBlockList().erase(BB);
       return true;
     }
 
@@ -1880,7 +1879,7 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
       while (isa<DbgInfoIntrinsic>(BBI))
         ++BBI;
       if (BBI->isTerminator()) // Terminator is the only non-phi instruction!
-        if (BB != &BB->getParent()->getEntryBlock())
+        if (BB != &Fn->getEntryBlock())
           if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
             return true;
       
@@ -2050,10 +2049,9 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
       }
 
       // If this block is now dead, remove it.
-      if (pred_begin(BB) == pred_end(BB) &&
-          BB != &BB->getParent()->getEntryBlock()) {
+      if (pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) {
         // We know there are no successors, so just nuke the block.
-        M->getBasicBlockList().erase(BB);
+        Fn->getBasicBlockList().erase(BB);
         return true;
       }
     }
diff --git a/test/Transforms/SimplifyCFG/2010-10-24-OnlyUnwindInEntry.ll b/test/Transforms/SimplifyCFG/2010-10-24-OnlyUnwindInEntry.ll
new file mode 100644
index 00000000000..ebacf2fe9a9
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/2010-10-24-OnlyUnwindInEntry.ll
@@ -0,0 +1,6 @@
+; RUN: opt %s -simplifycfg -disable-output
+; PR8445
+
+define void @test() {
+      unwind
+}