Index: lib/Analysis/InlineCost.cpp
===================================================================
--- lib/Analysis/InlineCost.cpp
+++ lib/Analysis/InlineCost.cpp
@@ -1307,7 +1307,7 @@
     // Bail out the moment we cross the threshold. This means we'll under-count
     // the cost, but only when undercounting doesn't matter.
     if (Cost > Threshold)
-      break;
+      return false;
 
     BasicBlock *BB = BBWorklist[Idx];
     if (BB->empty())
@@ -1373,7 +1373,7 @@
     // inlining.
     if (SingleBB && TI->getNumSuccessors() > 1) {
       // Take off the bonus we applied to the threshold.
-      Threshold -= SingleBBBonus;
+      Threshold = std::max(Threshold - SingleBBBonus, 0);
       SingleBB = false;
     }
   }
@@ -1388,10 +1388,12 @@
   // subtract the excess bonus, if any, from the Threshold before
   // comparing against Cost.
   if (NumVectorInstructions <= NumInstructions / 10)
-    Threshold -= FiftyPercentVectorBonus;
+    Threshold = std::max(Threshold - FiftyPercentVectorBonus, 0);
   else if (NumVectorInstructions <= NumInstructions / 2)
-    Threshold -= (FiftyPercentVectorBonus - TenPercentVectorBonus);
+    Threshold = std::max(
+        Threshold - (FiftyPercentVectorBonus - TenPercentVectorBonus), 0);
 
+  assert(Threshold >= 0 && "Inlinining threshold must be non-negative");
   return Cost < std::max(1, Threshold);
 }
 
Index: test/Transforms/Inline/inline_unreachable-2.ll
===================================================================
--- /dev/null
+++ test/Transforms/Inline/inline_unreachable-2.ll
@@ -0,0 +1,19 @@
+; RUN: opt < %s -inline -S | FileCheck %s
+
+; CHECK-LABEL: caller
+; CHECK: call void @callee
+define void @caller(i32 %a, i1 %b) #0 {
+  call void @callee(i32 %a, i1 %b)
+  unreachable
+}
+
+define void @callee(i32 %a, i1 %b) {
+  call void asm sideeffect "", ""()
+  br i1 %b, label %bb1, label %bb2
+bb1:
+  call void asm sideeffect "", ""()
+  ret void
+bb2:
+  call void asm sideeffect "", ""()
+  ret void
+}