diff --git a/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp b/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
--- a/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
+++ b/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
@@ -279,7 +279,7 @@
   std::vector<EncodingIDAndOpcode> VariableInstructions;
 
   // Map of well-known segment value to its delegate.
-  std::map<unsigned, std::unique_ptr<const FilterChooser>> FilterChooserMap;
+  std::map<uint64_t, std::unique_ptr<const FilterChooser>> FilterChooserMap;
 
   // Number of instructions which fall under FilteredInstructions category.
   unsigned NumFiltered;
@@ -305,7 +305,7 @@
   const FilterChooser &getVariableFC() const {
     assert(NumFiltered == 1);
     assert(FilterChooserMap.size() == 1);
-    return *(FilterChooserMap.find((unsigned)-1)->second);
+    return *(FilterChooserMap.find((uint64_t)-1)->second);
   }
 
   // Divides the decoding task into sub tasks and delegates them to the
@@ -603,7 +603,7 @@
     // Delegates to an inferior filter chooser for further processing on this
     // group of instructions whose segment values are variable.
     FilterChooserMap.insert(
-        std::make_pair(-1U, std::make_unique<FilterChooser>(
+        std::make_pair(-1ULL, std::make_unique<FilterChooser>(
                                 Owner->AllInstructions, VariableInstructions,
                                 Owner->Operands, BitValueArray, *Owner)));
   }
@@ -674,7 +674,7 @@
   for (auto &Filter : FilterChooserMap) {
     // Field value -1 implies a non-empty set of variable instructions.
     // See also recurse().
-    if (Filter.first == (unsigned)-1) {
+    if (Filter.first == (uint64_t)-1) {
       HasFallthrough = true;
 
       // Each scope should always have at least one filter value to check