[PATCH] D52100: [tblgen] Allow FixedLenDecoderEmitter to use APInt-like objects as InsnType

[Daniel Sanders via Phabricator via llvm-commits]

dsanders updated this revision to Diff 166497.
dsanders added a comment.

Add requirement for == and !=.
Add requirement for conversion to uint64_t. I'd like to remove this one again but it's currently necessary for field extraction
Remove conversion to bool. This proved to be very dangerous as it happily casts to any integral type via bool, silently truncating data.


Repository:
  rL LLVM

https://reviews.llvm.org/D52100

Files:
  utils/TableGen/FixedLenDecoderEmitter.cpp


Index: utils/TableGen/FixedLenDecoderEmitter.cpp
===================================================================
--- utils/TableGen/FixedLenDecoderEmitter.cpp
+++ utils/TableGen/FixedLenDecoderEmitter.cpp
@@ -2067,21 +2067,59 @@
 // using the VS compiler. It has a bug which causes the function
 // to be optimized out in some circustances. See llvm.org/pr38292
 static void emitFieldFromInstruction(formatted_raw_ostream &OS) {
-  OS << "// Helper function for extracting fields from encoded instructions.\n"
-     << "template<typename InsnType>\n"
+  OS << "// Helper functions for extracting fields from encoded instructions.\n"
+     << "// InsnType must either be integral or an APInt-like object that "
+        "must:\n"
+     << "// * Have a static const max_size_in_bits equal to the number of bits "
+        "in the\n"
+     << "//   encoding.\n"
+     << "// * be default-constructible and copy-constructible\n"
+     << "// * be constructible from a uint64_t\n"
+     << "// * be constructible from an APInt (this can be private)\n"
+     << "// * Support getBitsSet(loBit, hiBit)\n"
+     << "// * be convertible to uint64_t\n"
+     << "// * Support the ~, &, ==, !=, and |= operators with other objects of "
+        "the same type\n"
+     << "// * Support shift (<<, >>) with signed and unsigned integers on the "
+        "RHS\n"
+     << "// * Support put (<<) to raw_ostream&\n"
      << "#if defined(_MSC_VER) && !defined(__clang__)\n"
      << "__declspec(noinline)\n"
      << "#endif\n"
-     << "static InsnType fieldFromInstruction(InsnType insn, unsigned startBit,\n"
+     << "template<typename InsnType>\n"
+     << "static InsnType fieldFromInstruction(InsnType insn, unsigned "
+        "startBit,\n"
+     << "                                     unsigned numBits, "
+        "std::true_type) {\n"
+     << "  assert(startBit + numBits <= (sizeof(InsnType) * 8) &&\n"
+     << "         \"Instruction field out of bounds!\");\n"
+     << "  InsnType fieldMask;\n"
+     << "  if (numBits == sizeof(InsnType) * 8)\n"
+     << "    fieldMask = (InsnType)(-1LL);\n"
+     << "  else\n"
+     << "    fieldMask = (((InsnType)1 << numBits) - 1) << startBit;\n"
+     << "  return (insn & fieldMask) >> startBit;\n"
+     << "}\n"
+     << "\n"
+     << "template<typename InsnType>\n"
+     << "static InsnType fieldFromInstruction(InsnType insn, unsigned "
+        "startBit,\n"
+     << "                                     unsigned numBits, "
+        "std::false_type) {\n"
+     << "  assert(startBit + numBits <= InsnType::max_size_in_bits && "
+        "\"Instruction field out of bounds!\");\n"
+     << "  InsnType fieldMask = InsnType::getBitsSet(0, numBits);\n"
+     << "  return (insn >> startBit) & fieldMask;\n"
+     << "}\n"
+     << "\n"
+     << "template<typename InsnType>\n"
+     << "static InsnType fieldFromInstruction(InsnType insn, unsigned "
+        "startBit,\n"
      << "                                     unsigned numBits) {\n"
-     << "    assert(startBit + numBits <= (sizeof(InsnType)*8) &&\n"
-     << "           \"Instruction field out of bounds!\");\n"
-     << "    InsnType fieldMask;\n"
-     << "    if (numBits == sizeof(InsnType)*8)\n"
-     << "      fieldMask = (InsnType)(-1LL);\n"
-     << "    else\n"
-     << "      fieldMask = (((InsnType)1 << numBits) - 1) << startBit;\n"
-     << "    return (insn & fieldMask) >> startBit;\n"
+     << "  assert(startBit + numBits <= 64 && \"Cannot support >64-bit "
+        "extractions!\");\n"
+     << "  return fieldFromInstruction(insn, startBit, numBits, "
+        "std::is_integral<InsnType>());\n"
      << "}\n\n";
 }
 


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