Index: docs/LangRef.rst
===================================================================
--- docs/LangRef.rst
+++ docs/LangRef.rst
@@ -1488,6 +1488,27 @@
   of the called function.  Inter-procedural optimizations work as
   usual as long as they take into account the first two properties.
 
+More specific types of operand bundles are described below.
+
+Deoptimization Operand Bundles
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Deoptimization operand bundles are characterized by the ``"deopt``
+operand bundle tag.  These operand bundles represent an alternate
+"safe" continuation for the call site they're attached to, and can be
+used by a suitable runtime to deoptimize the compiled frame at the
+specified call site.  Exact details of deoptimization is out of scope
+for the language reference, but it usually involves rewriting a
+compiled frame into a set of interpreted frames.
+
+From the compiler's perspective, deoptimization operand bundles make
+the call sites they're attached to at least ``readonly``.  They read
+through all of their pointer typed operands (even if they're not
+otherwise escaped) and the entire visible heap.  Deoptimization
+operand bundles do not capture their operands except during
+deoptimization, in which case control will not be returned to the
+compiled frame.
+
 .. _moduleasm:
 
 Module-Level Inline Assembly
Index: include/llvm/IR/LLVMContext.h
===================================================================
--- include/llvm/IR/LLVMContext.h
+++ include/llvm/IR/LLVMContext.h
@@ -67,6 +67,14 @@
     MD_align = 17 // "align"
   };
 
+  // Known operand bundle tag IDs, which always have the same value.  All
+  // operand bundle tags that LLVM has special knowledge of are listed here.
+  // Additionally, this scheme allows LLVM to efficiently check for specific
+  // operand bundle tags without comparing strings.
+  enum {
+    OB_deopt = 0,  // "deopt"
+  };
+
   /// getMDKindID - Return a unique non-zero ID for the specified metadata kind.
   /// This ID is uniqued across modules in the current LLVMContext.
   unsigned getMDKindID(StringRef Name) const;
Index: lib/IR/LLVMContext.cpp
===================================================================
--- lib/IR/LLVMContext.cpp
+++ lib/IR/LLVMContext.cpp
@@ -127,6 +127,11 @@
   unsigned AlignID = getMDKindID("align");
   assert(AlignID == MD_align && "align kind id drifted");
   (void)AlignID;
+
+  auto *DeoptEntry = pImpl->getOrInsertBundleTag("deopt");
+  assert(DeoptEntry->second == LLVMContext::OB_deopt &&
+         "deopt operand bundle id drifted!");
+  (void)DeoptEntry;
 }
 LLVMContext::~LLVMContext() { delete pImpl; }
 
Index: lib/IR/Verifier.cpp
===================================================================
--- lib/IR/Verifier.cpp
+++ lib/IR/Verifier.cpp
@@ -2324,6 +2324,15 @@
     if (Intrinsic::ID ID = (Intrinsic::ID)F->getIntrinsicID())
       visitIntrinsicCallSite(ID, CS);
 
+  // Verify that a callsite has at most one "deopt" operand bundle.
+  bool FoundDeoptBundle = false;
+  for (unsigned i = 0, e = CS.getNumOperandBundles(); i < e; ++i) {
+    if (CS.getOperandBundleAt(i).getTagID() == LLVMContext::OB_deopt) {
+      Assert(!FoundDeoptBundle, "Multiple deopt operand bundles", I);
+      FoundDeoptBundle = true;
+    }
+  }
+
   visitInstruction(*I);
 }
 
Index: test/Verifier/operand-bundles.ll
===================================================================
--- test/Verifier/operand-bundles.ll
+++ test/Verifier/operand-bundles.ll
@@ -34,3 +34,16 @@
   %x = add i32 42, 1
   ret void
 }
+
+define void @f_deopt(i32* %ptr) {
+; CHECK: Multiple deopt operand bundles
+; CHECK-NEXT: call void @g() [ "deopt"(i32 42, i64 100, i32 %x), "deopt"(float 0.000000e+00, i64 100, i32 %l) ]
+; CHECK-NOT: call void @g() [ "deopt"(i32 42, i64 120, i32 %x) ]
+
+ entry:
+  %l = load i32, i32* %ptr
+  call void @g() [ "deopt"(i32 42, i64 100, i32 %x), "deopt"(float 0.0, i64 100, i32 %l) ]
+  call void @g() [ "deopt"(i32 42, i64 120) ]  ;; The verifier should not complain about this one
+  %x = add i32 42, 1
+  ret void
+}