[NFC][DecoderEmitter] Predicate generation code cleanup (#158140)

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.

Author: jurahul

llvm/test/TableGen/AsmPredicateCombining.td

@@ -63,19 +63,19 @@ def AsmPred4 : Predicate<"Pred4">, AssemblerPredicate<(all_of AsmCond4, (not (an
 // MATCHER-NEXT:   Features.set(Feature_AsmPred4Bit);
 
 def insn1 : TestInsn<1, [AsmPred1]>;
-// DISASS: return (Bits[arch::AsmCond1]);
+// DISASS: return FB[arch::AsmCond1];
 
 def insn2 : TestInsn<2, [AsmPred2]>;
-// DISASS: return (Bits[arch::AsmCond2a] && Bits[arch::AsmCond2b])
+// DISASS: return FB[arch::AsmCond2a] && FB[arch::AsmCond2b];
 
 def insn3 : TestInsn<3, [AsmPred3]>;
-// DISASS: return (Bits[arch::AsmCond3a] || Bits[arch::AsmCond3b])
+// DISASS: return FB[arch::AsmCond3a] || FB[arch::AsmCond3b];
 
 def insn4 : TestInsn<4, [AsmPred1, AsmPred2]>;
-// DISASS: return (Bits[arch::AsmCond1] && (Bits[arch::AsmCond2a] && Bits[arch::AsmCond2b]))
+// DISASS: return FB[arch::AsmCond1] && (FB[arch::AsmCond2a] && FB[arch::AsmCond2b]);
 
 def insn5 : TestInsn<5, [AsmPred1, AsmPred3]>;
-// DISASS: return (Bits[arch::AsmCond1] && (Bits[arch::AsmCond3a] || Bits[arch::AsmCond3b]))
+// DISASS: return FB[arch::AsmCond1] && (FB[arch::AsmCond3a] || FB[arch::AsmCond3b]);
 
 def insn6 : TestInsn<6, []>;
 def : InstAlias<"alias1", (insn6 R0)> { let Predicates = [AsmPred1]; }

llvm/test/TableGen/AsmPredicateCondsEmission.td

@@ -29,4 +29,4 @@ def foo : Instruction {
   let Predicates = [Pred1, Pred2];
 }
 
-// CHECK: return (Bits[arch::AssemblerCondition2]);
+// CHECK: return FB[arch::AssemblerCondition2];

llvm/utils/TableGen/Common/SubtargetFeatureInfo.cpp

@@ -190,8 +190,9 @@ void SubtargetFeatureInfo::emitMCPredicateCheck(
   bool ParenIfBinOp = range_size(MCPredicates) > 1;
   for (const Record *R : MCPredicates) {
     OS << LS;
-    emitFeaturesAux(TargetName, *R->getValueAsDag("AssemblerCondDag"),
-                    ParenIfBinOp, OS);
+    if (emitFeaturesAux(TargetName, *R->getValueAsDag("AssemblerCondDag"),
+                        ParenIfBinOp, OS))
+      PrintFatalError(R, "Invalid AssemblerCondDag!");
   }
 }
 
@@ -206,12 +207,14 @@ void SubtargetFeatureInfo::emitComputeAssemblerAvailableFeatures(
     OS << "const ";
   OS << "{\n";
   OS << "  FeatureBitset Features;\n";
-  for (const auto &SF : SubtargetFeatures) {
-    const SubtargetFeatureInfo &SFI = SF.second;
+  for (const SubtargetFeatureInfo &SFI : make_second_range(SubtargetFeatures)) {
+    const Record *Def = SFI.TheDef;
 
     OS << "  if (";
-    emitFeaturesAux(TargetName, *SFI.TheDef->getValueAsDag("AssemblerCondDag"),
-                    /*ParenIfBinOp=*/false, OS);
+    if (emitFeaturesAux(TargetName, *Def->getValueAsDag("AssemblerCondDag"),
+                        /*ParenIfBinOp=*/false, OS))
+      PrintFatalError(Def, "Invalid AssemblerCondDag!");
+
     OS << ")\n";
     OS << "    Features.set(" << SFI.getEnumBitName() << ");\n";
   }

llvm/utils/TableGen/DecoderEmitter.cpp

@@ -16,6 +16,7 @@
 #include "Common/CodeGenTarget.h"
 #include "Common/InfoByHwMode.h"
 #include "Common/InstructionEncoding.h"
+#include "Common/SubtargetFeatureInfo.h"
 #include "Common/VarLenCodeEmitterGen.h"
 #include "TableGenBackends.h"
 #include "llvm/ADT/APInt.h"
@@ -519,8 +520,6 @@ 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;
@@ -839,12 +838,12 @@ void DecoderEmitter::emitPredicateFunction(formatted_raw_ostream &OS,
   // The predicate function is just a big switch statement based on the
   // input predicate index.
   OS << "static bool checkDecoderPredicate(unsigned Idx, const FeatureBitset "
-        "&Bits) {\n";
+        "&FB) {\n";
   OS << "  switch (Idx) {\n";
   OS << "  default: llvm_unreachable(\"Invalid index!\");\n";
   for (const auto &[Index, Predicate] : enumerate(Predicates)) {
     OS << "  case " << Index << ":\n";
-    OS << "    return (" << Predicate << ");\n";
+    OS << "    return " << Predicate << ";\n";
   }
   OS << "  }\n";
   OS << "}\n\n";
@@ -1134,41 +1133,19 @@ bool DecoderTableBuilder::emitPredicateMatchAux(const Init &Val,
   return true;
 }
 
+// Returns true if there was any predicate emitted.
 bool DecoderTableBuilder::emitPredicateMatch(raw_ostream &OS,
                                              unsigned EncodingID) const {
-  const ListInit *Predicates =
-      Encodings[EncodingID].getRecord()->getValueAsListInit("Predicates");
-  bool IsFirstEmission = true;
-  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()))
-      continue;
-
-    if (!IsFirstEmission)
-      OS << " && ";
-    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;
+  std::vector<const Record *> Predicates =
+      Encodings[EncodingID].getRecord()->getValueAsListOfDefs("Predicates");
+  auto It = llvm::find_if(Predicates, [](const Record *R) {
+    return R->getValueAsBit("AssemblerMatcherPredicate");
+  });
+  bool AnyAsmPredicate = It != Predicates.end();
+  if (!AnyAsmPredicate)
+    return false;
+  SubtargetFeatureInfo::emitMCPredicateCheck(OS, Target.getName(), Predicates);
+  return true;
 }
 
 unsigned DecoderTableBuilder::getPredicateIndex(StringRef Predicate) const {
@@ -1186,15 +1163,11 @@ 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.