Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5565,9 +5565,21 @@
   }
 
   if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
-    ConstantRange X = getRangeRef(Add->getOperand(0), SignHint);
-    for (unsigned i = 1, e = Add->getNumOperands(); i != e; ++i)
-      X = X.add(getRangeRef(Add->getOperand(i), SignHint));
+    ConstantRange X(BitWidth, /*isFullSet=*/true);
+    if (maskFlags(Add->getNoWrapFlags(), SCEV::FlagNSW) == SCEV::FlagNSW) {
+      if (auto *C = dyn_cast<SCEVConstant>(Add->getOperand(0))) {
+        X = getRangeRef(Add->getOperand(1), SignHint);
+        X = X.addWithNoSignedWrap(C->getAPInt());
+      } else if (auto *C = dyn_cast<SCEVConstant>(Add->getOperand(1))) {
+        X = getRangeRef(Add->getOperand(0), SignHint);
+        X = X.addWithNoSignedWrap(C->getAPInt());
+      }
+    } else {
+      //TODO: handle SCEV::FLAGNUW.
+      X = getRangeRef(Add->getOperand(0), SignHint);
+      for (unsigned i = 1, e = Add->getNumOperands(); i != e; ++i)
+        X = X.add(getRangeRef(Add->getOperand(i), SignHint));
+    }
     return setRange(Add, SignHint,
                     ConservativeResult.intersectWith(X, RangeType));
   }
Index: llvm/test/Analysis/ScalarEvolution/max-trip-count.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/max-trip-count.ll
+++ llvm/test/Analysis/ScalarEvolution/max-trip-count.ll
@@ -342,7 +342,7 @@
 define void @changing_end_bound3(i32 %start, i32* %n_addr, i32* %addr) {
 ; CHECK-LABEL: Determining loop execution counts for: @changing_end_bound3
 ; CHECK: Loop %loop: Unpredictable backedge-taken count.
-; CHECK: Loop %loop: max backedge-taken count is 1073741823
+; CHECK: Loop %loop: max backedge-taken count is 1073741822
 entry:
   br label %loop
 
Index: llvm/test/Analysis/ScalarEvolution/trip-count12.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/trip-count12.ll
+++ llvm/test/Analysis/ScalarEvolution/trip-count12.ll
@@ -2,7 +2,7 @@
 
 ; CHECK: Determining loop execution counts for: @test
 ; CHECK: Loop %for.body: backedge-taken count is ((-2 + %len)<nsw> /u 2)
-; CHECK: Loop %for.body: max backedge-taken count is 1073741823
+; CHECK: Loop %for.body: max backedge-taken count is 1073741822
 
 define zeroext i16 @test(i16* nocapture %p, i32 %len) nounwind readonly {
 entry:
Index: llvm/test/Analysis/ScalarEvolution/trip-count9.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/trip-count9.ll
+++ llvm/test/Analysis/ScalarEvolution/trip-count9.ll
@@ -180,7 +180,7 @@
 
 ; CHECK: Determining loop execution counts for: @nsw_startx
 ; CHECK: Loop %loop: backedge-taken count is (-1 + (-1 * %x) + ((1 + %x)<nsw> smax %n))
-; CHECK: Loop %loop: max backedge-taken count is -1
+; CHECK: Loop %loop: max backedge-taken count is -2
 define void @nsw_startx(i4 %n, i4 %x) {
 entry:
   %s = icmp sgt i4 %n, 0
@@ -196,7 +196,7 @@
 
 ; CHECK: Determining loop execution counts for: @nsw_startx_step2
 ; CHECK: Loop %loop: backedge-taken count is ((-1 + (-1 * %x) + ((2 + %x)<nsw> smax %n)) /u 2)
-; CHECK: Loop %loop: max backedge-taken count is 7
+; CHECK: Loop %loop: max backedge-taken count is 6
 define void @nsw_startx_step2(i4 %n, i4 %x) {
 entry:
   %s = icmp sgt i4 %n, 0
@@ -227,6 +227,7 @@
   ret void
 }
 
+; CHECK-LABEL: even_step2
 ; CHECK: Determining loop execution counts for: @even_step2
 ; CHECK: Loop %loop: backedge-taken count is ((-1 + (2 * %n)) /u 2)
 ; CHECK: Loop %loop: max backedge-taken count is 2
@@ -382,7 +383,7 @@
 
 ; CHECK: Determining loop execution counts for: @even_nsw_startx
 ; CHECK: Loop %loop: backedge-taken count is (-1 + (-1 * %x) + ((1 + %x)<nsw> smax (2 * %n)))
-; CHECK: Loop %loop: max backedge-taken count is -2
+; CHECK: Loop %loop: max backedge-taken count is -3
 define void @even_nsw_startx(i4 %n, i4 %x) {
 entry:
   %m = shl i4 %n, 1
@@ -399,7 +400,7 @@
 
 ; CHECK: Determining loop execution counts for: @even_nsw_startx_step2
 ; CHECK: Loop %loop: backedge-taken count is ((-1 + (-1 * %x) + ((2 + %x)<nsw> smax (2 * %n))) /u 2)
-; CHECK: Loop %loop: max backedge-taken count is 7
+; CHECK: Loop %loop: max backedge-taken count is 6
 define void @even_nsw_startx_step2(i4 %n, i4 %x) {
 entry:
   %m = shl i4 %n, 1