[llvm] [TableGen][DecoderEmitter] Add option to emit type-specialized `decodeToMCInst` (PR #146593)

[Rahul Joshi via llvm-commits]

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@@ -2537,6 +2559,67 @@ handleHwModesUnrelatedEncodings(const CodeGenInstruction *Instr,
     break;
   }
 }
+SmallVector<NonTemplatedInsnType>
+DecoderEmitter::parseNonTemplatedInsnTypes(BitwidthSet &InstrBitwidths) {
+  SmallVector<NonTemplatedInsnType> Parsed;
+
+  const Record *InstructionSet = Target.getInstructionSet();
+  std::vector<StringRef> InsnCPPTypes =
+      InstructionSet->getValueAsListOfStrings("InsnCPPTypes");
+
+  if (InsnCPPTypes.empty()) {
+    // If no `InsnCPPTypes` is specified in the instruction info,
+    // create a type-spec with empty values, which will trigger generation of
+    // a templated `decodeToMCInst`.
+    Parsed.emplace_back();
+    return Parsed;
+  }
+
+  // Use field locations for error reporting.
+  SMLoc CPPTypesLoc = InstructionSet->getFieldLoc("InsnCPPTypes");
+  SMLoc BitwidthsLoc = InstructionSet->getFieldLoc("InsnBitwidths");
+
+  const ListInit *InsnBitwidths =
+      InstructionSet->getValueAsListInit("InsnBitwidths");
+
+  Parsed.reserve(InsnCPPTypes.size());
+  BitwidthSet OptionBitwidths;
+
+  for (const auto &[CPPType, BWL] :
+       zip_equal(InsnCPPTypes, InsnBitwidths->getElements())) {
+    BitwidthSet Bitwidths;
+    if (CPPType.empty())
+      PrintFatalError(CPPTypesLoc,
+                      "CPP Type cannot be empty in `InsnCPPTypes`");
+    const auto *BitwidthList = dyn_cast<ListInit>(BWL);
+    if (!BitwidthList || BitwidthList->empty())
+      PrintFatalError(BitwidthsLoc,
+                      "No bitwidths specified for InsnCPPType : " + CPPType);
+
+    for (int64_t Bitwidth : BitwidthList->getAsListOfInts()) {
+      if (!OptionBitwidths.insert(Bitwidth).second)
+        PrintFatalError(BitwidthsLoc,
+                        "Bitwidth " + Twine(Bitwidth) + " already specified.");
+
+      if (!InstrBitwidths.contains(Bitwidth))
+        PrintFatalError(BitwidthsLoc, "No instruction of bitwidth " +
+                                          Twine(Bitwidth) + " supported.");
+      InstrBitwidths.erase(Bitwidth);
+      Bitwidths.insert(Bitwidth);
+    }
+    Parsed.emplace_back(NonTemplatedInsnType{CPPType, Bitwidths});
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jurahul wrote:

It gave a compiler error when I tried, but I have addressed it now by adding a constructor to the struct.

https://github.com/llvm/llvm-project/pull/146593