From f5102a0f088e7c96f7028bf7ca1c24975c314fff Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 28 Nov 2008 19:54:49 +0000
Subject: [PATCH] don't call MergeBasicBlockIntoOnlyPred on a block whose only
 predecessor is itself.  This doesn't make sense, and this is a dead infinite
 loop anyway.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60210 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/CodeGenPrepare.cpp      | 20 ++++++++++---------
 lib/Transforms/Scalar/JumpThreading.cpp       |  3 ++-
 .../JumpThreading/2008-11-28-InfLoop.ll       | 17 ++++++++++++++++
 3 files changed, 30 insertions(+), 10 deletions(-)
 create mode 100644 test/Transforms/JumpThreading/2008-11-28-InfLoop.ll

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index e6b7497d6bc..7079fa828b5 100644
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -205,16 +205,18 @@ void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) {
   // If the destination block has a single pred, then this is a trivial edge,
   // just collapse it.
   if (BasicBlock *SinglePred = DestBB->getSinglePredecessor()) {
-    // Remember if SinglePred was the entry block of the function.  If so, we
-    // will need to move BB back to the entry position.
-    bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
-    MergeBasicBlockIntoOnlyPred(DestBB);
+    if (SinglePred != DestBB) {
+      // Remember if SinglePred was the entry block of the function.  If so, we
+      // will need to move BB back to the entry position.
+      bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
+      MergeBasicBlockIntoOnlyPred(DestBB);
 
-    if (isEntry && BB != &BB->getParent()->getEntryBlock())
-      BB->moveBefore(&BB->getParent()->getEntryBlock());
-    
-    DOUT << "AFTER:\n" << *DestBB << "\n\n\n";
-    return;
+      if (isEntry && BB != &BB->getParent()->getEntryBlock())
+        BB->moveBefore(&BB->getParent()->getEntryBlock());
+      
+      DOUT << "AFTER:\n" << *DestBB << "\n\n\n";
+      return;
+    }
   }
 
   // Otherwise, we have multiple predecessors of BB.  Update the PHIs in DestBB
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 5de5fb3b776..114603dabb0 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -164,7 +164,8 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
   // because now the condition in this block can be threaded through
   // predecessors of our predecessor block.
   if (BasicBlock *SinglePred = BB->getSinglePredecessor())
-    if (SinglePred->getTerminator()->getNumSuccessors() == 1) {
+    if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
+        SinglePred != BB) {
       // Remember if SinglePred was the entry block of the function.  If so, we
       // will need to move BB back to the entry position.
       bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
diff --git a/test/Transforms/JumpThreading/2008-11-28-InfLoop.ll b/test/Transforms/JumpThreading/2008-11-28-InfLoop.ll
new file mode 100644
index 00000000000..974b9ef7747
--- /dev/null
+++ b/test/Transforms/JumpThreading/2008-11-28-InfLoop.ll
@@ -0,0 +1,17 @@
+; RUN: llvm-as < %s | opt -jump-threading | llvm-dis
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+target triple = "i386-apple-darwin9.5"
+	%struct.decContext = type { i32 }
+	%struct.decNumber = type { i32, i32 }
+
+define i32 @decNumberPower(%struct.decNumber* %res, %struct.decNumber* %lhs, %struct.decNumber* %rhs, %struct.decContext* %set) nounwind {
+entry:
+	br i1 true, label %decDivideOp.exit, label %bb7.i
+
+bb7.i:		; preds = %bb7.i, %entry
+	br label %bb7.i
+
+decDivideOp.exit:		; preds = %entry
+	ret i32 undef
+}