From 755edefea9551f0bd6ff887c75ca0695579fddbd Mon Sep 17 00:00:00 2001
From: ZihengJiang <jzhtomas@gmail.com>
Date: Tue, 21 Feb 2017 03:53:07 +0000
Subject: [PATCH 1/3] [FIX] add CombineInterval<Div>

---
 src/arithmetic/int_set.cc | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/src/arithmetic/int_set.cc b/src/arithmetic/int_set.cc
index 8fdba6650f25..a9e5ef2d8d18 100644
--- a/src/arithmetic/int_set.cc
+++ b/src/arithmetic/int_set.cc
@@ -251,6 +251,32 @@ inline IntSet CombineInterval<Mul>(Interval a, Interval b) {
   return IntSet::everything();
 }
 
+template<>
+inline IntSet CombineInterval<Div>(Interval a, Interval b) {
+  if (a.is_single_point() && b.is_single_point()) {
+    return IntSet::single_point(ComputeExpr<Div>(a.min, b.min));
+  }
+  if (b.is_single_point()) {
+    if (is_zero(b.min)) {
+      LOG(WARNING) << "Return Everything in CombineInterval Div";
+      return IntSet::everything();
+    }
+    if (is_one(b.min)) return IntervalSet::make(a);
+    Expr e1 = a.has_lower_bound() ? ComputeExpr<Div>(a.min, b.min) : a.min;
+    Expr e2 = a.has_upper_bound() ? ComputeExpr<Div>(a.max, b.min) : a.min;
+    if (is_positive_const(b.min)) {
+      return IntervalSet::make(e1, e2);
+    } else if (is_negative_const(b.min)) {
+      return IntervalSet::make(e2, e1);
+    } else if (a.is_bounded()) {
+      Expr cmp = b.min >= make_zero(b.min.type().element_of());
+      return IntervalSet::make(select(cmp, e1, e2), select(cmp, e2, e1));
+    }
+  }
+  LOG(WARNING) << "Return Everything in CombineInterval Div";
+  return IntSet::everything();
+}
+
 template<>
 inline IntSet CombineInterval<Max>(Interval a, Interval b) {
   if (a.is_single_point() && b.is_single_point()) {

From 566c6f97a126cee1246570ec149f2dde33912134 Mon Sep 17 00:00:00 2001
From: ZihengJiang <jzhtomas@gmail.com>
Date: Tue, 21 Feb 2017 18:10:31 +0000
Subject: [PATCH 2/3] fix error message and add comment about rounding

---
 src/arithmetic/int_set.cc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/arithmetic/int_set.cc b/src/arithmetic/int_set.cc
index a9e5ef2d8d18..fb96d3ec09f6 100644
--- a/src/arithmetic/int_set.cc
+++ b/src/arithmetic/int_set.cc
@@ -258,12 +258,12 @@ inline IntSet CombineInterval<Div>(Interval a, Interval b) {
   }
   if (b.is_single_point()) {
     if (is_zero(b.min)) {
-      LOG(WARNING) << "Return Everything in CombineInterval Div";
-      return IntSet::everything();
+      LOG(FATAL) << "Divide by zero in CombineInterval Div";
     }
     if (is_one(b.min)) return IntervalSet::make(a);
     Expr e1 = a.has_lower_bound() ? ComputeExpr<Div>(a.min, b.min) : a.min;
-    Expr e2 = a.has_upper_bound() ? ComputeExpr<Div>(a.max, b.min) : a.min;
+    Expr e2 = a.has_upper_bound() ? ComputeExpr<Div>(a.max, b.min) : a.max;
+    // This is relaxiation due to set is inclusive
     if (is_positive_const(b.min)) {
       return IntervalSet::make(e1, e2);
     } else if (is_negative_const(b.min)) {

From c17c0ab2660a9b8c41592fb10421a52d633b0da1 Mon Sep 17 00:00:00 2001
From: ZihengJiang <jzhtomas@gmail.com>
Date: Tue, 21 Feb 2017 18:37:00 +0000
Subject: [PATCH 3/3] fix comment

---
 src/arithmetic/int_set.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/arithmetic/int_set.cc b/src/arithmetic/int_set.cc
index fb96d3ec09f6..db6c75642f3b 100644
--- a/src/arithmetic/int_set.cc
+++ b/src/arithmetic/int_set.cc
@@ -236,7 +236,7 @@ inline IntSet CombineInterval<Mul>(Interval a, Interval b) {
     if (is_one(b.min)) return IntervalSet::make(a);
     Expr e1 = a.has_lower_bound() ? ComputeExpr<Mul>(a.min, b.min) : a.min;
     Expr e2 = a.has_upper_bound() ? ComputeExpr<Mul>(a.max, b.min) : a.max;
-    // This is relaxiation
+    // no relaxation is needed in here due to set is inclusive
     // TODO(tqchen): consider convert to StrideSet.
     if (is_positive_const(b.min)) {
       return IntervalSet::make(e1, e2);
@@ -263,7 +263,7 @@ inline IntSet CombineInterval<Div>(Interval a, Interval b) {
     if (is_one(b.min)) return IntervalSet::make(a);
     Expr e1 = a.has_lower_bound() ? ComputeExpr<Div>(a.min, b.min) : a.min;
     Expr e2 = a.has_upper_bound() ? ComputeExpr<Div>(a.max, b.min) : a.max;
-    // This is relaxiation due to set is inclusive
+    // no relaxation is needed in here due to set is inclusive
     if (is_positive_const(b.min)) {
       return IntervalSet::make(e1, e2);
     } else if (is_negative_const(b.min)) {