Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -3282,10 +3282,17 @@
   // atomic operations are guaranteed to terminate on most platforms
   // and most functions terminate.
 
+  if (ImmutableCallSite CS = ImmutableCallSite(I))
+    // NB! This assumes that a function cannot have an infinite loop that does
+    // not contain side effects.  As far as I can tell, this isn't a new
+    // assumption (e.g. we will DCE readnone and readonly calls).
+    return CS.doesNotThrow() && CS.onlyReadsMemory();
+
+  if (auto *II = dyn_cast<IntrinsicInst>(I))
+    if (II->getIntrinsicID() == Intrinsic::dbg_value)
+      return true;
+
   return !I->isAtomic() &&       // atomics may never succeed on some platforms
-         !isa<CallInst>(I) &&    // could throw and might not terminate
-         !isa<InvokeInst>(I) &&  // might not terminate and could throw to
-                                 //   non-successor (see bug 24185 for details).
          !isa<ResumeInst>(I) &&  // has no successors
          !isa<ReturnInst>(I);    // has no successors
 }
Index: test/Analysis/ScalarEvolution/flags-from-poison.ll
===================================================================
--- test/Analysis/ScalarEvolution/flags-from-poison.ll
+++ test/Analysis/ScalarEvolution/flags-from-poison.ll
@@ -1,5 +1,7 @@
 ; RUN: opt < %s -S -analyze -scalar-evolution | FileCheck %s
 
+declare void @unknown()
+
 ; Positive and negative tests for inferring flags like nsw from
 ; reasoning about how a poison value from overflow would trigger
 ; undefined behavior.
@@ -35,6 +37,63 @@
   ret void
 }
 
+define void @test-add-nsw-callinst-0(float* %input, i32 %offset, i32 %numIterations) {
+; CHECK-LABEL: @test-add-nsw-callinst-0
+entry:
+  br label %loop
+loop:
+  %i = phi i32 [ %nexti, %loop ], [ 0, %entry ]
+  ; We do not know whether @unknown() will return or throw or
+  ; infinitely loop, so we cannot infer undefined behavior if %index32
+  ; is poison.
+  call void @unknown()
+
+; CHECK: %index32 =
+; CHECK: --> {%offset,+,1}<nw>
+  %index32 = add nsw i32 %i, %offset
+
+; CHECK: %index64 =
+; CHECK: --> (sext i32 {%offset,+,1}<nw><%loop> to i64)
+  %index64 = sext i32 %index32 to i64
+
+  %ptr = getelementptr inbounds float, float* %input, i64 %index64
+  %nexti = add nsw i32 %i, 1
+  %f = load float, float* %ptr, align 4
+  call void @foo()
+  %exitcond = icmp eq i32 %nexti, %numIterations
+  br i1 %exitcond, label %exit, label %loop
+exit:
+  ret void
+}
+
+define void @test-add-nsw-callinst-1(float* %input, i32 %offset, i32 %numIterations) {
+; CHECK-LABEL: @test-add-nsw-callinst-1
+entry:
+  br label %loop
+loop:
+  %i = phi i32 [ %nexti, %loop ], [ 0, %entry ]
+  ; We know that the call to @unknown will not throw or have an
+  ; infinite loop, so we can conclude UB if %index32 is poison.
+  call void @unknown() nounwind readonly
+
+; CHECK: %index32 =
+; CHECK: --> {%offset,+,1}<nsw>
+  %index32 = add nsw i32 %i, %offset
+
+; CHECK: %index64 =
+; CHECK: --> {(sext i32 %offset to i64),+,1}<nsw>
+  %index64 = sext i32 %index32 to i64
+
+  %ptr = getelementptr inbounds float, float* %input, i64 %index64
+  %nexti = add nsw i32 %i, 1
+  %f = load float, float* %ptr, align 4
+  call void @foo()
+  %exitcond = icmp eq i32 %nexti, %numIterations
+  br i1 %exitcond, label %exit, label %loop
+exit:
+  ret void
+}
+
 ; Example where an add should get the nuw flag.
 define void @test-add-nuw(float* %input, i32 %offset, i32 %numIterations) {
 ; CHECK-LABEL: @test-add-nuw