Index: llvm/trunk/lib/Analysis/InlineCost.cpp
===================================================================
--- llvm/trunk/lib/Analysis/InlineCost.cpp
+++ llvm/trunk/lib/Analysis/InlineCost.cpp
@@ -1296,7 +1296,7 @@
   else if (NumVectorInstructions <= NumInstructions / 2)
     Threshold -= (FiftyPercentVectorBonus - TenPercentVectorBonus);
 
-  return Cost < Threshold;
+  return Cost <= std::max(0, Threshold);
 }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
Index: llvm/trunk/test/Transforms/Inline/zero-cost.ll
===================================================================
--- llvm/trunk/test/Transforms/Inline/zero-cost.ll
+++ llvm/trunk/test/Transforms/Inline/zero-cost.ll
@@ -0,0 +1,17 @@
+; RUN: opt -inline -S %s | FileCheck %s
+
+define void @f() {
+entry:
+  tail call void @g()
+  unreachable
+
+; CHECK-LABEL: @f
+; CHECK-NOT: call
+; CHECK: unreachable
+}
+
+define void @g() {
+entry:
+  unreachable
+}
+