From a5e27f80282d240817d651347a2ddc80a03ee9ce Mon Sep 17 00:00:00 2001
From: Devang Patel <dpatel@apple.com>
Date: Wed, 9 Jul 2008 00:12:01 +0000
Subject: [PATCH] If loop induction variable's start value is less then its
 exit value then do not split the loop.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53265 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopIndexSplit.cpp      | 13 ++++++++++
 .../LoopIndexSplit/2008-05-19-IndVar.ll       |  2 +-
 .../2008-07-08-MisCompilation.ll              | 25 +++++++++++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/LoopIndexSplit/2008-07-08-MisCompilation.ll

diff --git a/lib/Transforms/Scalar/LoopIndexSplit.cpp b/lib/Transforms/Scalar/LoopIndexSplit.cpp
index 45d4900ca86..135ce33ee6f 100644
--- a/lib/Transforms/Scalar/LoopIndexSplit.cpp
+++ b/lib/Transforms/Scalar/LoopIndexSplit.cpp
@@ -384,6 +384,19 @@ void LoopIndexSplit::findLoopConditionals() {
     BasicBlock *Preheader = L->getLoopPreheader();
     StartValue = IndVar->getIncomingValueForBlock(Preheader);
   }
+
+  // If start value is more then exit value where induction variable
+  // increments by 1 then we are potentially dealing with an infinite loop.
+  // Do not index split this loop.
+  if (ExitCondition) {
+    ConstantInt *SV = dyn_cast<ConstantInt>(StartValue);
+    ConstantInt *EV = 
+      dyn_cast<ConstantInt>(ExitCondition->getOperand(ExitValueNum));
+    if (SV && EV && SV->getSExtValue() > EV->getSExtValue())
+      ExitCondition = NULL;
+    else if (EV && EV->isZero())
+      ExitCondition = NULL;
+  }
 }
 
 /// Find condition inside a loop that is suitable candidate for index split.
diff --git a/test/Transforms/LoopIndexSplit/2008-05-19-IndVar.ll b/test/Transforms/LoopIndexSplit/2008-05-19-IndVar.ll
index 8aa2e52b3fe..c4678b47ac4 100644
--- a/test/Transforms/LoopIndexSplit/2008-05-19-IndVar.ll
+++ b/test/Transforms/LoopIndexSplit/2008-05-19-IndVar.ll
@@ -24,7 +24,7 @@ bb4.i:		; preds = %bb.i
 	br label %bb6.i
 bb6.i:		; preds = %bb4.i, %bb.i
 	%tmp8.i = add i16 %g_2.tmp.0.i, 1		; <i16> [#uses=3]
-	%tmp11.i = icmp sgt i16 %tmp8.i, 0		; <i1> [#uses=1]
+	%tmp11.i = icmp sgt i16 %tmp8.i, 42		; <i1> [#uses=1]
 	br i1 %tmp11.i, label %bb.i, label %return.loopexit.i
 return.loopexit.i:		; preds = %bb6.i
 	%tmp8.i.lcssa = phi i16 [ %tmp8.i, %bb6.i ]		; <i16> [#uses=1]
diff --git a/test/Transforms/LoopIndexSplit/2008-07-08-MisCompilation.ll b/test/Transforms/LoopIndexSplit/2008-07-08-MisCompilation.ll
new file mode 100644
index 00000000000..7592511a290
--- /dev/null
+++ b/test/Transforms/LoopIndexSplit/2008-07-08-MisCompilation.ll
@@ -0,0 +1,25 @@
+; RUN: llvm-as < %s | opt -loop-index-split -stats -disable-output | not grep "1 loop-index-split"
+; PR 2487
+@g_6 = external global i32		; <i32*> [#uses=1]
+
+define void @func_1() nounwind  {
+entry:
+	br label %bb
+
+bb:		; preds = %bb4, %entry
+	%l_3.0 = phi i8 [ 0, %entry ], [ %tmp6, %bb4 ]		; <i8> [#uses=2]
+	%tmp1 = icmp eq i8 %l_3.0, 0		; <i1> [#uses=1]
+	br i1 %tmp1, label %bb3, label %bb4
+
+bb3:		; preds = %bb
+	store i32 1, i32* @g_6, align 4
+	br label %bb4
+
+bb4:		; preds = %bb3, %bb
+	%tmp6 = add i8 %l_3.0, 1		; <i8> [#uses=2]
+	%tmp9 = icmp sgt i8 %tmp6, -1		; <i1> [#uses=1]
+	br i1 %tmp9, label %bb, label %return
+
+return:		; preds = %bb4
+	ret void
+}