[SelectionDAG] Encode CheckPatternPredicate num in VBR format to expand the range it can represents

[zixuan-wu]

Summary

As the pattern predicate number is growing, SelectionDAG MatcherTable type of char is too small to hold the number directly. So use VBR format to encode the num like what CheckOrImm does.

[craig.topper]

This is definitely not the right fix. We can use a variable bit encoding for the predicate like we do for CheckInteger, CheckAndImm, CheckOrImm, etc.

[zixuan-wu]

Address comments.

[craig.topper]

Can you measure the size impact to the X86 and RISC-V tables?

[zixuan-wu]

In D156967#4557928, @craig.topper wrote:

Can you measure the size impact to the X86 and RISC-V tables?

Here is the data after patch.

Before :
RISCV - // Total Array size is 2368318 bytes
X86 -   // Total Array size is 680816 bytes

After:
RISCV - // Total Array size is 2372208 bytes
X86 -   // Total Array size is 686351 bytes

[craig.topper]

Hold up on this I might have an alternate proposal.

[craig.topper]

I've posted https://reviews.llvm.org/D157196 as alternative that won't impact X86 or other targets that already have more than 128 predicates.

[bogner]

I think we can abandon this and go with Craig's two-opcode approach.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

LLVM_ATTRIBUTE_ALWAYS_INLINE static bool CheckChildSame(
   return ::CheckSame(MatcherTable, MatcherIndex, N.getOperand(ChildNo),
                      RecordedNodes);
 }
 
 /// CheckPatternPredicate - Implements OP_CheckPatternPredicate.
 LLVM_ATTRIBUTE_ALWAYS_INLINE static bool
 CheckPatternPredicate(const unsigned char *MatcherTable, unsigned &MatcherIndex,
                       const SelectionDAGISel &SDISel) {
-  return SDISel.CheckPatternPredicate(MatcherTable[MatcherIndex++]);
+  int64_t Val = MatcherTable[MatcherIndex++];
+  if (Val & 128)
+    Val = GetVBR(Val, MatcherTable, MatcherIndex);
+
+  return SDISel.CheckPatternPredicate(Val);
 }
 
 /// CheckNodePredicate - Implements OP_CheckNodePredicate.
 LLVM_ATTRIBUTE_ALWAYS_INLINE static bool
 CheckNodePredicate(const unsigned char *MatcherTable, unsigned &MatcherIndex,
                    const SelectionDAGISel &SDISel, SDNode *N) {
   return SDISel.CheckNodePredicate(N, MatcherTable[MatcherIndex++]);
 }

llvm/utils/TableGen/DAGISelMatcherEmitter.cpp

EmitMatcher(const Matcher *N, const unsigned Indent, unsigned CurrentIdx,
   case Matcher::CheckChildSame:
     OS << "OPC_CheckChild"
        << cast<CheckChildSameMatcher>(N)->getChildNo() << "Same, "
        << cast<CheckChildSameMatcher>(N)->getMatchNumber() << ",\n";
     return 2;
 
   case Matcher::CheckPatternPredicate: {
     StringRef Pred =cast<CheckPatternPredicateMatcher>(N)->getPredicate();
-    OS << "OPC_CheckPatternPredicate, " << getPatternPredicate(Pred) << ',';
+    OS << "OPC_CheckPatternPredicate, ";
+    unsigned Bytes =
+        1 + EmitVBRValue(getPatternPredicate(Pred), OS);
     if (!OmitComments)
       OS << " // " << Pred;
     OS << '\n';
-    return 2;
+    return Bytes;
   }
   case Matcher::CheckPredicate: {
     TreePredicateFn Pred = cast<CheckPredicateMatcher>(N)->getPredicate();
     unsigned OperandBytes = 0;
 
     if (Pred.usesOperands()) {
       unsigned NumOps = cast<CheckPredicateMatcher>(N)->getNumOperands();
       OS << "OPC_CheckPredicateWithOperands, " << NumOps << "/*#Ops*/, ";