Index: llvm/test/Reduce/no-replace-intrinsic-callee-with-undef.ll
===================================================================
--- /dev/null
+++ llvm/test/Reduce/no-replace-intrinsic-callee-with-undef.ll
@@ -0,0 +1,24 @@
+; It's invalid to have a non-intrinsic call with a metadata argument,
+; so it's unproductive to replace the users of the intrinsic
+; declaration with undef.
+
+; RUN: llvm-reduce --test FileCheck --test-arg --check-prefixes=CHECK-ALL,CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t 2> %t.log
+; RUN: FileCheck -check-prefix=STDERR %s < %t.log
+; RUN: cat %t | FileCheck -implicit-check-not=uninteresting --check-prefixes=CHECK-ALL,CHECK-FINAL %s
+
+; STDERR-NOT: Function has metadata parameter but isn't an intrinsic
+
+declare i32 @llvm.amdgcn.reloc.constant(metadata)
+declare void @uninteresting()
+
+define i32 @interesting() {
+entry:
+  ; CHECK-INTERESTINGNESS-LABEL: define i32 @interesting(
+  ; CHECK-INTERESTINGNESS: call
+
+  ; CHECK-FINAL: %call = call i32 @llvm.amdgcn.reloc.constant(metadata !"arst")
+  ; CHECK-FINAL-NEXT: ret i32 %call
+  %call = call i32 @llvm.amdgcn.reloc.constant(metadata !"arst")
+  call void @uninteresting()
+  ret i32 %call
+}
Index: llvm/tools/llvm-reduce/deltas/ReduceFunctions.cpp
===================================================================
--- llvm/tools/llvm-reduce/deltas/ReduceFunctions.cpp
+++ llvm/tools/llvm-reduce/deltas/ReduceFunctions.cpp
@@ -30,7 +30,13 @@
   // Record all out-of-chunk functions.
   std::vector<std::reference_wrapper<Function>> FuncsToRemove;
   copy_if(Program->functions(), std::back_inserter(FuncsToRemove),
-          [&O](auto &unused) { return !O.shouldKeep(); });
+          [&O](Function &F) {
+            // Intrinsics don't have function bodies that are useful to
+            // reduce. Additionally, intrinsics may have additional operand
+            // constraints, and changing to an arbitrary call may radically
+            // change codegen.
+            return !F.isIntrinsic() && !O.shouldKeep();
+          });
 
   // Then, drop body of each of them. We want to batch this and do nothing else
   // here so that minimal number of remaining exteranal uses will remain.
@@ -53,8 +59,12 @@
   errs() << "----------------------------\n";
   errs() << "Function Index Reference:\n";
   int FunctionCount = 0;
-  for (auto &F : *Program)
-    errs() << "\t" << ++FunctionCount << ": " << F.getName() << "\n";
+  for (auto &F : *Program) {
+    if (F.isIntrinsic())
+      continue;
+
+    errs() << '\t' << ++FunctionCount << ": " << F.getName() << '\n';
+  }
 
   errs() << "----------------------------\n";
   return FunctionCount;