From 4d3bba5be47ec159ad3489793248acc812d75575 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Thu, 28 Jun 2012 23:44:57 +0000
Subject: [PATCH] If the step value is a constant zero, the loop isn't going to
 terminate. Fixes the assert reported in PR13228!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159393 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp              |  2 +-
 .../ScalarEvolution/how-far-to-zero.ll        | 27 +++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 test/Analysis/ScalarEvolution/how-far-to-zero.ll

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 886812be5fa..09410496d31 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -5484,7 +5484,7 @@ ScalarEvolution::HowFarToZero(const SCEV *V, const Loop *L) {
   // to 0, it must be counting down to equal 0. Consequently, N = Start / -Step.
   // We have not yet seen any such cases.
   const SCEVConstant *StepC = dyn_cast<SCEVConstant>(Step);
-  if (StepC == 0)
+  if (StepC == 0 || StepC->getValue()->equalsInt(0))
     return getCouldNotCompute();
 
   // For positive steps (counting up until unsigned overflow):
diff --git a/test/Analysis/ScalarEvolution/how-far-to-zero.ll b/test/Analysis/ScalarEvolution/how-far-to-zero.ll
new file mode 100644
index 00000000000..07af88ffbeb
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/how-far-to-zero.ll
@@ -0,0 +1,27 @@
+; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
+
+; PR13228
+define void @f() nounwind uwtable readnone {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond, %entry
+  %c.0 = phi i8 [ 1, %entry ], [ 0, %for.cond ]
+  %i.0 = phi i8 [ 0, %entry ], [ %inc, %for.cond ]
+  %lnot = icmp eq i8 %i.0, 0
+  %inc = add i8 %i.0, 1
+  br i1 %lnot, label %for.cond, label %while.cond
+
+while.cond:                                       ; preds = %while.body, %for.cond
+  %b.2 = phi i8 [ %add, %while.body ], [ 0, %for.cond ]
+  br i1 undef, label %while.end, label %while.body
+
+while.body:                                       ; preds = %while.cond
+  %add = add i8 %b.2, %c.0
+  %tobool7 = icmp eq i8 %add, 0
+  br i1 %tobool7, label %while.end, label %while.cond
+
+while.end:                                        ; preds = %while.body, %while.cond
+  ret void
+}
+;CHECK: Loop %while.cond: <multiple exits> Unpredictable backedge-taken count.