[llvm] [TableGen][DecoderEmitter] Avoid using a sentinel value (PR #153986)

[Sergei Barannikov via llvm-commits]

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@@ -746,46 +744,30 @@ void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
   TableInfo.Table.insertULEB128(StartBit);
   TableInfo.Table.push_back(NumBits);
 
-  // If the NO_FIXED_SEGMENTS_SENTINEL is present, we need to add a new scope
-  // for this filter. Otherwise, we can skip adding a new scope and any
-  // patching added will automatically be added to the enclosing scope.
-
-  // If NO_FIXED_SEGMENTS_SENTINEL is present, it will be last entry in
-  // FilterChooserMap.
-
+  // If VariableFC is present, we need to add a new scope for this filter.
+  // Otherwise, we can skip adding a new scope and any patching added will
+  // automatically be added to the enclosing scope.
   const uint64_t LastFilter = FilterChooserMap.rbegin()->first;
-  bool HasFallthrough = LastFilter == NO_FIXED_SEGMENTS_SENTINEL;
-  if (HasFallthrough)
-    TableInfo.pushScope();
+  if (VariableFC)
+    TableInfo.FixupStack.emplace_back();
 
   DecoderTable &Table = TableInfo.Table;
 
   size_t PrevFilter = 0;
   for (const auto &[FilterVal, Delegate] : FilterChooserMap) {
-    // Field value NO_FIXED_SEGMENTS_SENTINEL implies a non-empty set of
-    // variable instructions. See also recurse().
-    if (FilterVal == NO_FIXED_SEGMENTS_SENTINEL) {
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s-barannikov wrote:

This was effectively moved below the loop. Hiding whitespace changes makes it a little easier to review.

https://github.com/llvm/llvm-project/pull/153986