diff --git a/llvm/test/TableGen/simplify-patfrag.td b/llvm/test/TableGen/simplify-patfrag.td
new file mode 100644
--- /dev/null
+++ b/llvm/test/TableGen/simplify-patfrag.td
@@ -0,0 +1,38 @@
+// RUN: llvm-tblgen -gen-dag-isel -I %p/../../include %s 2>&1 | FileCheck %s
+
+include "llvm/Target/Target.td"
+
+// Minimal Target definition
+def DemoInstrInfo : InstrInfo;
+def Demo : Target {
+  let InstructionSet = DemoInstrInfo;
+}
+
+// Some registers which can hold ints or floats
+foreach i = 0-7 in
+  def "R" # i: Register<"r" # i>;
+def GPR : RegisterClass<"Demo", [i32, f32], 32, (sequence "R%u", 0, 7)>;
+
+// Instruction to convert an int to a float
+def i2f : Instruction {
+  let Size = 2;
+  let OutOperandList = (outs GPR:$dst);
+  let InOperandList = (ins GPR:$src);
+  let AsmString = "i2f $dst, $src";
+}
+
+// Some kind of special type-conversion node supported by this target
+def specialconvert : SDNode<"TEST_TARGET_ISD::SPECIAL_CONVERT", SDTUnaryOp>;
+
+// A PatFrags that matches either bitconvert or the special version
+def anyconvert : PatFrags<(ops node:$src),
+                          [(bitconvert node:$src),
+                           (specialconvert node:$src)]>;
+
+// And a rule that matches that PatFrag and turns it into i2f
+def : Pat<(f32 (anyconvert (i32 GPR:$val))), (i2f GPR:$val)>;
+
+// CHECK: SwitchOpcode{{.*}}ISD::BITCAST
+// CHECK: MorphNodeTo1{{.*}}i2f
+// CHECK: SwitchOpcode{{.*}}TEST_TARGET_ISD::SPECIAL_CONVERT
+// CHECK: MorphNodeTo1{{.*}}i2f
diff --git a/llvm/utils/TableGen/CodeGenDAGPatterns.cpp b/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
--- a/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
+++ b/llvm/utils/TableGen/CodeGenDAGPatterns.cpp
@@ -2918,8 +2918,15 @@
 
   // If we have a bitconvert with a resolved type and if the source and
   // destination types are the same, then the bitconvert is useless, remove it.
+  //
+  // We make an exception if the types are completely empty. This can come up
+  // when the pattern being simplified is in the Fragments list of a PatFrags,
+  // so that the operand is just an untyped "node". In that situation we leave
+  // bitconverts unsimplified, and simplify them later once the fragment is
+  // expanded into its true context.
   if (N->getOperator()->getName() == "bitconvert" &&
       N->getExtType(0).isValueTypeByHwMode(false) &&
+      !N->getExtType(0).empty() &&
       N->getExtType(0) == N->getChild(0)->getExtType(0) &&
       N->getName().empty()) {
     N = N->getChildShared(0);