[NFC][DecoderEmitter] Predicate generation code cleanup

[jurahul]

Eliminate doesOpcodeNeedPredicate and instead have emitPredicateMatch return true if any predicates were generated. Delegate actual predicate generation in emitPredicateMatch to SubtargetFeatureInfo::emitMCPredicateCheck. Additionally, remove the redundant parenthesis around the predicate conditions in the generated checkDecoderPredicate function.

Note that for ARM/AMDGPU this reduces the total # of predicates generated by a few. It seems the old code would sometimes generate duplicate predicates which were identical in semantics but one had an extra pair of parentheses (i..e, X and (X)). emitMCPredicateCheck does not seems to have that issue.

[llvmbot]

@llvm/pr-subscribers-tablegen

Author: Rahul Joshi (jurahul)

Changes

Use ListSeparator to join individual predicated with &&. Eliminate doesOpcodeNeedPredicate and instead have emitPredicateMatch return true if any predicates were generated.

---

Full diff: https://github.com/llvm/llvm-project/pull/158140.diff

1 Files Affected:

• (modified) llvm/utils/TableGen/DecoderEmitter.cpp (+7-25)

diff --git a/llvm/utils/TableGen/DecoderEmitter.cpp b/llvm/utils/TableGen/DecoderEmitter.cpp
index 8747d02ac892b..96957aed60df3 100644
--- a/llvm/utils/TableGen/DecoderEmitter.cpp
+++ b/llvm/utils/TableGen/DecoderEmitter.cpp
@@ -635,8 +635,6 @@ class DecoderTableBuilder {
 
   bool emitPredicateMatch(raw_ostream &OS, unsigned EncodingID) const;
 
-  bool doesOpcodeNeedPredicate(unsigned EncodingID) const;
-
   void emitPredicateTableEntry(unsigned EncodingID) const;
 
   void emitSoftFailTableEntry(unsigned EncodingID) const;
@@ -1221,7 +1219,8 @@ bool DecoderTableBuilder::emitPredicateMatch(raw_ostream &OS,
                                              unsigned EncodingID) const {
   const ListInit *Predicates =
       Encodings[EncodingID].getRecord()->getValueAsListInit("Predicates");
-  bool IsFirstEmission = true;
+  ListSeparator LS(" && ");
+  bool AnyPredicate = false;
   for (unsigned i = 0; i < Predicates->size(); ++i) {
     const Record *Pred = Predicates->getElementAsRecord(i);
     if (!Pred->getValue("AssemblerMatcherPredicate"))
@@ -1230,28 +1229,13 @@ bool DecoderTableBuilder::emitPredicateMatch(raw_ostream &OS,
     if (!isa<DagInit>(Pred->getValue("AssemblerCondDag")->getValue()))
       continue;
 
-    if (!IsFirstEmission)
-      OS << " && ";
+    AnyPredicate = true;
+    OS << LS;
     if (emitPredicateMatchAux(*Pred->getValueAsDag("AssemblerCondDag"),
                               Predicates->size() > 1, OS))
       PrintFatalError(Pred->getLoc(), "Invalid AssemblerCondDag!");
-    IsFirstEmission = false;
-  }
-  return !Predicates->empty();
-}
-
-bool DecoderTableBuilder::doesOpcodeNeedPredicate(unsigned EncodingID) const {
-  const ListInit *Predicates =
-      Encodings[EncodingID].getRecord()->getValueAsListInit("Predicates");
-  for (unsigned i = 0; i < Predicates->size(); ++i) {
-    const Record *Pred = Predicates->getElementAsRecord(i);
-    if (!Pred->getValue("AssemblerMatcherPredicate"))
-      continue;
-
-    if (isa<DagInit>(Pred->getValue("AssemblerCondDag")->getValue()))
-      return true;
   }
-  return false;
+  return AnyPredicate;
 }
 
 unsigned DecoderTableBuilder::getPredicateIndex(StringRef Predicate) const {
@@ -1269,15 +1253,13 @@ unsigned DecoderTableBuilder::getPredicateIndex(StringRef Predicate) const {
 }
 
 void DecoderTableBuilder::emitPredicateTableEntry(unsigned EncodingID) const {
-  if (!doesOpcodeNeedPredicate(EncodingID))
-    return;
-
   // Build up the predicate string.
   SmallString<256> Predicate;
   // FIXME: emitPredicateMatch() functions can take a buffer directly rather
   // than a stream.
   raw_svector_ostream PS(Predicate);
-  emitPredicateMatch(PS, EncodingID);
+  if (!emitPredicateMatch(PS, EncodingID))
+    return;
 
   // Figure out the index into the predicate table for the predicate just
   // computed.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[s-barannikov]

LGTM

[s-barannikov]

(The description needs an update.)

[jurahul]

(The description needs an update.)

Updated, thanks

[s-barannikov]

Sorry, missed it. emitPredicateMatchAux is now unused.

[jurahul]

Thanks, will fix

…

On Mon, Sep 15, 2025 at 8:13 PM Sergei Barannikov ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In llvm/utils/TableGen/DecoderEmitter.cpp <#158140 (comment)>: > @@ -1134,41 +1133,19 @@ bool DecoderTableBuilder::emitPredicateMatchAux(const Init &Val, return true; } Sorry, missed it. emitPredicateMatchAux is now unused. — Reply to this email directly, view it on GitHub <#158140 (review)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/APRMUB4ESQQ7J67UA5P27QL3S554LAVCNFSM6AAAAACGIYVINGVHI2DSMVQWIX3LMV43YUDVNRWFEZLROVSXG5CSMV3GSZLXHMZTEMRWHEYTOMZYGY> . You are receiving this because you modified the open/close state.Message ID: ***@***.***>