Index: lib/Transforms/Utils/InlineFunction.cpp
===================================================================
--- lib/Transforms/Utils/InlineFunction.cpp
+++ lib/Transforms/Utils/InlineFunction.cpp
@@ -1029,6 +1029,10 @@
       CalledFunc->isDeclaration() || // call, or call to a vararg function!
       CalledFunc->getFunctionType()->isVarArg()) return false;
 
+  // The inliner does not know how to inline through calls with operand bundles.
+  if (CS.hasOperandBundles())
+    return false;
+
   // If the call to the callee cannot throw, set the 'nounwind' flag on any
   // calls that we inline.
   bool MarkNoUnwind = CS.doesNotThrow();
Index: test/Feature/OperandBundles/inliner-conservative.ll
===================================================================
--- /dev/null
+++ test/Feature/OperandBundles/inliner-conservative.ll
@@ -0,0 +1,17 @@
+; RUN: opt -S -inline < %s | FileCheck %s
+
+; Check that the inliner does not inline through arbitrary unknown
+; operand bundles.
+
+define i32 @callee() {
+ entry:
+  ret i32 2
+}
+
+define i32 @caller() {
+; CHECK: @caller(
+ entry:
+; CHECK: call i32 @callee() [ "unknown"() ]
+  %x = call i32 @callee() [ "unknown"() ]
+  ret i32 %x
+}