[mlir][bytecode] Avoid recording null arglocs & realloc opnames.

For block arg locs a common case is no/uknown location (where the producer
signifies they don't care about blockarg location). Also avoid needing to
dynamically resize opnames during parsing.

Assumed to be post lazy loading change, so chose version 3.

Differential Revision: https://reviews.llvm.org/D151038

mlir/docs/BytecodeFormat.md

@@ -154,6 +154,7 @@ dialects that were also referenced.
 dialect_section {
   numDialects: varint,
   dialectNames: varint[],
+  numTotalOpNames: varint,
   opNames: op_name_group[]
 }
 
@@ -444,8 +445,8 @@ block_arguments {
 }
 
 block_argument {
-  typeIndex: varint,
-  location: varint
+  typeAndLocation: varint, // (type << 1) | (hasLocation)
+  location: varint? // Optional, else unknown location
 }
 ```
 

mlir/include/mlir/Bytecode/Encoding.h

@@ -29,7 +29,7 @@ enum {
   kMinSupportedVersion = 0,
 
   /// The current bytecode version.
-  kVersion = 3,
+  kVersion = 4,
 
   /// An arbitrary value used to fill alignment padding.
   kAlignmentByte = 0xCB,

mlir/lib/Bytecode/Reader/BytecodeReader.cpp

@@ -1603,6 +1603,14 @@ BytecodeReader::Impl::parseDialectSection(ArrayRef<uint8_t> sectionData) {
     opNames.emplace_back(dialect, opName);
     return success();
   };
+  // Avoid re-allocation in bytecode version > 3 where the number of ops are
+  // known.
+  if (version > 3) {
+    uint64_t numOps;
+    if (failed(sectionReader.parseVarInt(numOps)))
+      return failure();
+    opNames.reserve(numOps);
+  }
   while (!sectionReader.empty())
     if (failed(parseDialectGrouping(sectionReader, dialects, parseOpName)))
       return failure();
@@ -2175,13 +2183,25 @@ LogicalResult BytecodeReader::Impl::parseBlockArguments(EncodingReader &reader,
   argTypes.reserve(numArgs);
   argLocs.reserve(numArgs);
 
+  Location unknownLoc = UnknownLoc::get(config.getContext());
   while (numArgs--) {
     Type argType;
-    LocationAttr argLoc;
-    if (failed(parseType(reader, argType)) ||
-        failed(parseAttribute(reader, argLoc)))
-      return failure();
-
+    LocationAttr argLoc = unknownLoc;
+    if (version > 3) {
+      // Parse the type with hasLoc flag to determine if it has type.
+      uint64_t typeIdx;
+      bool hasLoc;
+      if (failed(reader.parseVarIntWithFlag(typeIdx, hasLoc)) ||
+          !(argType = attrTypeReader.resolveType(typeIdx)))
+        return failure();
+      if (hasLoc && failed(parseAttribute(reader, argLoc)))
+        return failure();
+    } else {
+      // All args has type and location.
+      if (failed(parseType(reader, argType)) ||
+          failed(parseAttribute(reader, argLoc)))
+        return failure();
+    }
     argTypes.push_back(argType);
     argLocs.push_back(argLoc);
   }

mlir/lib/Bytecode/Writer/BytecodeWriter.cpp

@@ -585,6 +585,9 @@ void BytecodeWriter::writeDialectSection(EncodingEmitter &emitter) {
                                  std::move(versionEmitter));
   }
 
+  if (config.bytecodeVersion > 3)
+    dialectEmitter.emitVarInt(size(numberingState.getOpNames()));
+
   // Emit the referenced operation names grouped by dialect.
   auto emitOpName = [&](OpNameNumbering &name) {
     dialectEmitter.emitVarInt(stringSection.insert(name.name.stripDialect()));
@@ -670,8 +673,16 @@ void BytecodeWriter::writeBlock(EncodingEmitter &emitter, Block *block) {
   if (hasArgs) {
     emitter.emitVarInt(args.size());
     for (BlockArgument arg : args) {
-      emitter.emitVarInt(numberingState.getNumber(arg.getType()));
-      emitter.emitVarInt(numberingState.getNumber(arg.getLoc()));
+      Location argLoc = arg.getLoc();
+      if (config.bytecodeVersion > 3) {
+        emitter.emitVarIntWithFlag(numberingState.getNumber(arg.getType()),
+                                   !isa<UnknownLoc>(argLoc));
+        if (!isa<UnknownLoc>(argLoc))
+          emitter.emitVarInt(numberingState.getNumber(argLoc));
+      } else {
+        emitter.emitVarInt(numberingState.getNumber(arg.getType()));
+        emitter.emitVarInt(numberingState.getNumber(argLoc));
+      }
     }
     if (config.bytecodeVersion > 2) {
       uint64_t maskOffset = emitter.size();
@@ -755,7 +766,7 @@ void BytecodeWriter::writeOp(EncodingEmitter &emitter, Operation *op) {
 
     for (Region &region : op->getRegions()) {
       // If the region is not isolated from above, or we are emitting bytecode
-      // targetting version <2, we don't use a section.
+      // targeting version <2, we don't use a section.
       if (!isIsolatedFromAbove || config.bytecodeVersion < 2) {
         writeRegion(emitter, &region);
         continue;

mlir/test/Bytecode/general.mlir

@@ -32,7 +32,7 @@
   }
   "bytecode.branch"()[^secondBlock] : () -> ()
 
-^secondBlock(%arg1: i32, %arg2: !bytecode.int, %arg3: !pdl.operation):
+^secondBlock(%arg1: i32 loc(unknown), %arg2: !bytecode.int, %arg3: !pdl.operation loc(unknown)):
   "bytecode.regions"() ({
     "bytecode.operands"(%arg1, %arg2, %arg3) : (i32, !bytecode.int, !pdl.operation) -> ()
     "bytecode.return"() : () -> ()

mlir/test/Bytecode/invalid/invalid-structure.mlir

@@ -9,7 +9,7 @@
 //===--------------------------------------------------------------------===//
 
 // RUN: not mlir-opt %S/invalid-structure-version.mlirbc 2>&1 | FileCheck %s --check-prefix=VERSION
-// VERSION: bytecode version 127 is newer than the current version 3
+// VERSION: bytecode version 127 is newer than the current version
 
 //===--------------------------------------------------------------------===//
 // Producer