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
@@ -226,6 +226,8 @@
 
 namespace {
 
+static const uint64_t NO_FIXED_SEGMENTS_SENTINEL = -1ULL;
+
 class FilterChooser;
 
 /// Filter - Filter works with FilterChooser to produce the decoding tree for
@@ -279,7 +281,7 @@
   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 +307,7 @@
   const FilterChooser &getVariableFC() const {
     assert(NumFiltered == 1);
     assert(FilterChooserMap.size() == 1);
-    return *(FilterChooserMap.find((unsigned)-1)->second);
+    return *(FilterChooserMap.find(NO_FIXED_SEGMENTS_SENTINEL)->second);
   }
 
   // Divides the decoding task into sub tasks and delegates them to the
@@ -602,10 +604,9 @@
 
     // 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>(
-                                Owner->AllInstructions, VariableInstructions,
-                                Owner->Operands, BitValueArray, *Owner)));
+    FilterChooserMap.insert(std::make_pair(NO_FIXED_SEGMENTS_SENTINEL,
+        std::make_unique<FilterChooser>(Owner->AllInstructions,
+            VariableInstructions, Owner->Operands, BitValueArray, *Owner)));
   }
 
   // No need to recurse for a singleton filtered instruction.
@@ -674,7 +675,7 @@
   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 == NO_FIXED_SEGMENTS_SENTINEL) {
       HasFallthrough = true;
 
       // Each scope should always have at least one filter value to check