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optimize generated Go code to avoid heap allocations #8744

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6958504
opt(idl_gen_go): avoid allocations in accesses in generated code
Oct 24, 2025
9f4bd86
regenerate code
Oct 24, 2025
4e4fbc4
further cleanup
Oct 30, 2025
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24 changes: 9 additions & 15 deletions grpc/examples/go/greeter/models/HelloReply.go
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24 changes: 9 additions & 15 deletions grpc/examples/go/greeter/models/HelloRequest.go
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106 changes: 40 additions & 66 deletions src/idl_gen_go.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -186,7 +186,7 @@ class GoGenerator : public BaseGenerator {
// Most field accessors need to retrieve and test the field offset first,
// this is the prefix code for that.
std::string OffsetPrefix(const FieldDef& field) {
return "{\n\to := flatbuffers.UOffsetT(rcv._tab.Offset(" +
return "{\n\to := flatbuffers.UOffsetT(rcv.Offset(" +
NumToString(field.value.offset) + "))\n\tif o != 0 {\n";
}

Expand All @@ -198,7 +198,6 @@ class GoGenerator : public BaseGenerator {

// _ is reserved in flatbuffers field names, so no chance of name
// conflict:
code += "_tab ";
code += struct_def.fixed ? "flatbuffers.Struct" : "flatbuffers.Table";
code += "\n}\n\n";
}
Expand Down Expand Up @@ -323,21 +322,20 @@ class GoGenerator : public BaseGenerator {

for (int i = 0; i < 2; i++) {
code += "func Get" + size_prefix[i] + "RootAs" + struct_type;
code += "(buf []byte, offset flatbuffers.UOffsetT) ";
code += "*" + struct_type + "";
code += " {\n";
code += "(buf []byte, offset flatbuffers.UOffsetT) (x ";
code += struct_type + "";
code += ") {\n";
if (i == 0) {
code += "\tn := flatbuffers.GetUOffsetT(buf[offset:])\n";
} else {
code +=
"\tn := "
"flatbuffers.GetUOffsetT(buf[offset+flatbuffers.SizeUint32:])\n";
}
code += "\tx := &" + struct_type + "{}\n";
if (i == 0) {
code += "\tx.Init(buf, n+offset)\n";
code += "\tx.Table = flatbuffers.Table{Bytes: buf, Pos: n+offset}\n";
} else {
code += "\tx.Init(buf, n+offset+flatbuffers.SizeUint32)\n";
code += "\tx.Table = flatbuffers.Table{Bytes: buf, Pos: n+offset+flatbuffers.SizeUint32}\n";
}
code += "\treturn x\n";
code += "}\n\n";
Expand Down Expand Up @@ -371,24 +369,8 @@ class GoGenerator : public BaseGenerator {
GenReceiver(struct_def, code_ptr);
code += " Init(buf []byte, i flatbuffers.UOffsetT) ";
code += "{\n";
code += "\trcv._tab.Bytes = buf\n";
code += "\trcv._tab.Pos = i\n";
code += "}\n\n";
}

// Implement the table accessor
void GenTableAccessor(const StructDef& struct_def, std::string* code_ptr) {
std::string& code = *code_ptr;

GenReceiver(struct_def, code_ptr);
code += " Table() flatbuffers.Table ";
code += "{\n";

if (struct_def.fixed) {
code += "\treturn rcv._tab.Table\n";
} else {
code += "\treturn rcv._tab\n";
}
code += "\trcv.Bytes = buf\n";
code += "\trcv.Pos = i\n";
code += "}\n\n";
}

Expand All @@ -400,7 +382,7 @@ class GoGenerator : public BaseGenerator {
GenReceiver(struct_def, code_ptr);
code += " " + namer_.Function(field) + "Length(";
code += ") int " + OffsetPrefix(field);
code += "\t\treturn rcv._tab.VectorLen(o)\n\t}\n";
code += "\t\treturn rcv.VectorLen(o)\n\t}\n";
code += "\treturn 0\n}\n\n";
}

Expand All @@ -412,7 +394,7 @@ class GoGenerator : public BaseGenerator {
GenReceiver(struct_def, code_ptr);
code += " " + namer_.Function(field) + "Bytes(";
code += ") []byte " + OffsetPrefix(field);
code += "\t\treturn rcv._tab.ByteVector(o + rcv._tab.Pos)\n\t}\n";
code += "\t\treturn rcv.ByteVector(o + rcv.Pos)\n\t}\n";
code += "\treturn nil\n}\n\n";
}

Expand All @@ -426,7 +408,7 @@ class GoGenerator : public BaseGenerator {
code += "() " + TypeName(field) + " {\n";
code += "\treturn " +
CastToEnum(field.value.type,
getter + "(rcv._tab.Pos + flatbuffers.UOffsetT(" +
getter + "(rcv.Pos + flatbuffers.UOffsetT(" +
NumToString(field.value.offset) + "))");
code += "\n}\n";
}
Expand All @@ -445,7 +427,7 @@ class GoGenerator : public BaseGenerator {
} else {
code += "\t\treturn ";
}
code += CastToEnum(field.value.type, getter + "(o + rcv._tab.Pos)");
code += CastToEnum(field.value.type, getter + "(o + rcv.Pos)");
if (field.IsScalarOptional()) {
code += "\n\t\treturn &v";
}
Expand All @@ -467,7 +449,7 @@ class GoGenerator : public BaseGenerator {
code += "\tif obj == nil {\n";
code += "\t\tobj = new(" + TypeName(field) + ")\n";
code += "\t}\n";
code += "\tobj.Init(rcv._tab.Bytes, rcv._tab.Pos+";
code += "\tobj.Init(rcv.Bytes, rcv.Pos+";
code += NumToString(field.value.offset) + ")";
code += "\n\treturn obj\n";
code += "}\n";
Expand All @@ -480,19 +462,14 @@ class GoGenerator : public BaseGenerator {
std::string& code = *code_ptr;
GenReceiver(struct_def, code_ptr);
code += " " + namer_.Function(field);
code += "(obj *";
code += TypeName(field);
code += ") *" + TypeName(field) + " " + OffsetPrefix(field);
code += "() (obj " + TypeName(field) + ", ok bool) " + OffsetPrefix(field);
if (field.value.type.struct_def->fixed) {
code += "\t\tx := o + rcv._tab.Pos\n";
code += "\t\tx := o + rcv.Pos\n";
} else {
code += "\t\tx := rcv._tab.Indirect(o + rcv._tab.Pos)\n";
code += "\t\tx := rcv.Indirect(o + rcv.Pos)\n";
}
code += "\t\tif obj == nil {\n";
code += "\t\t\tobj = new(" + TypeName(field) + ")\n";
code += "\t\t}\n";
code += "\t\tobj.Init(rcv._tab.Bytes, x)\n";
code += "\t\treturn obj\n\t}\n\treturn nil\n";
code += "\t\tobj.Init(rcv.Bytes, x)\n\t\tok = true\n";
code += "\t}\n\treturn\n";
code += "}\n\n";
}

Expand All @@ -504,7 +481,7 @@ class GoGenerator : public BaseGenerator {
code += " " + namer_.Function(field);
code += "() " + TypeName(field) + " ";
code += OffsetPrefix(field) + "\t\treturn " + GenGetter(field.value.type);
code += "(o + rcv._tab.Pos)\n\t}\n\treturn nil\n";
code += "(o + rcv.Pos)\n\t}\n\treturn nil\n";
code += "}\n\n";
}

Expand All @@ -530,17 +507,16 @@ class GoGenerator : public BaseGenerator {

GenReceiver(struct_def, code_ptr);
code += " " + namer_.Function(field);
code += "(obj *" + TypeName(field);
code += ", j int) bool " + OffsetPrefix(field);
code += "\t\tx := rcv._tab.Vector(o)\n";
code += "(j int) (obj " + TypeName(field) + ", ok bool) " + OffsetPrefix(field);
code += "\t\tx := rcv.Vector(o)\n";
code += "\t\tx += flatbuffers.UOffsetT(j) * ";
code += NumToString(InlineSize(vectortype)) + "\n";
if (!(vectortype.struct_def->fixed)) {
code += "\t\tx = rcv._tab.Indirect(x)\n";
code += "\t\tx = rcv.Indirect(x)\n";
}
code += "\t\tobj.Init(rcv._tab.Bytes, x)\n";
code += "\t\treturn true\n\t}\n";
code += "\treturn false\n";
code += "\t\tobj.Init(rcv.Bytes, x)\n";
code += "\t\tok = true\n\t}\n";
code += "\treturn\n";
code += "}\n\n";
}

Expand All @@ -566,9 +542,9 @@ class GoGenerator : public BaseGenerator {
code += "(obj *" + TypeName(field);
code += ", key " + NativeType(key_field.value.type) + ") bool " +
OffsetPrefix(field);
code += "\t\tx := rcv._tab.Vector(o)\n";
code += "\t\tx := rcv.Vector(o)\n";
code += "\t\treturn ";
code += "obj.LookupByKey(key, x, rcv._tab.Bytes)\n";
code += "obj.LookupByKey(key, x, rcv.Bytes)\n";
code += "\t}\n";
code += "\treturn false\n";
code += "}\n\n";
Expand All @@ -585,7 +561,7 @@ class GoGenerator : public BaseGenerator {
code += " " + namer_.Function(field);
code += "(j int) " + TypeName(field) + " ";
code += OffsetPrefix(field);
code += "\t\ta := rcv._tab.Vector(o)\n";
code += "\t\ta := rcv.Vector(o)\n";
code += "\t\treturn " +
CastToEnum(field.value.type,
GenGetter(field.value.type) +
Expand Down Expand Up @@ -806,12 +782,12 @@ class GoGenerator : public BaseGenerator {
const FieldDef& field, std::string* code_ptr) {
std::string& code = *code_ptr;
std::string setter =
"rcv._tab.Mutate" + namer_.Method(GenTypeBasic(field.value.type));
"rcv.Mutate" + namer_.Method(GenTypeBasic(field.value.type));
GenReceiver(struct_def, code_ptr);
code += " Mutate" + namer_.Function(field);
code +=
"(n " + GenTypeGet(field.value.type) + ") bool {\n\treturn " + setter;
code += "(rcv._tab.Pos+flatbuffers.UOffsetT(";
code += "(rcv.Pos+flatbuffers.UOffsetT(";
code += NumToString(field.value.offset) + "), ";
code += CastToBaseType(field.value.type, "n") + ")\n}\n\n";
}
Expand All @@ -820,7 +796,7 @@ class GoGenerator : public BaseGenerator {
void MutateScalarFieldOfTable(const StructDef& struct_def,
const FieldDef& field, std::string* code_ptr) {
std::string& code = *code_ptr;
std::string setter = "rcv._tab.Mutate" +
std::string setter = "rcv.Mutate" +
namer_.Method(GenTypeBasic(field.value.type)) + "Slot";
GenReceiver(struct_def, code_ptr);
code += " Mutate" + namer_.Function(field);
Expand All @@ -837,12 +813,12 @@ class GoGenerator : public BaseGenerator {
std::string& code = *code_ptr;
auto vectortype = field.value.type.VectorType();
std::string setter =
"rcv._tab.Mutate" + namer_.Method(GenTypeBasic(vectortype));
"rcv.Mutate" + namer_.Method(GenTypeBasic(vectortype));
GenReceiver(struct_def, code_ptr);
code += " Mutate" + namer_.Function(field);
code += "(j int, n " + TypeName(field) + ") bool ";
code += OffsetPrefix(field);
code += "\t\ta := rcv._tab.Vector(o)\n";
code += "\t\ta := rcv.Vector(o)\n";
code += "\t\treturn " + setter + "(";
code += "a+flatbuffers.UOffsetT(j*";
code += NumToString(InlineSize(vectortype)) + "), ";
Expand Down Expand Up @@ -907,8 +883,6 @@ class GoGenerator : public BaseGenerator {
// Generate the Init method that sets the field in a pre-existing
// accessor object. This is to allow object reuse.
InitializeExisting(struct_def, code_ptr);
// Generate _tab accessor
GenTableAccessor(struct_def, code_ptr);

// Generate struct fields accessors
for (auto it = struct_def.fields.vec.begin();
Expand Down Expand Up @@ -1282,13 +1256,13 @@ class GoGenerator : public BaseGenerator {
code +=
"\tt." + field_field + " = rcv." + field_field + "(nil).UnPack()\n";
} else if (field.value.type.base_type == BASE_TYPE_UNION) {
const std::string field_table = field_var + "Table";
code += "\t" + field_table + " := flatbuffers.Table{}\n";
const std::string fielde = field_var + "Table";
code += "\t" + fielde + " := flatbuffers.Table{}\n";
code +=
"\tif rcv." + namer_.Method(field) + "(&" + field_table + ") {\n";
"\tif rcv." + namer_.Method(field) + "(&" + fielde + ") {\n";
code += "\t\tt." + field_field + " = rcv." +
namer_.Method(field.name + UnionTypeFieldSuffix()) +
"().UnPack(" + field_table + ")\n";
"().UnPack(" + fielde + ")\n";
code += "\t}\n";
} else {
FLATBUFFERS_ASSERT(0);
Expand Down Expand Up @@ -1399,13 +1373,13 @@ class GoGenerator : public BaseGenerator {
std::string GenGetter(const Type& type) {
switch (type.base_type) {
case BASE_TYPE_STRING:
return "rcv._tab.ByteVector";
return "rcv.ByteVector";
case BASE_TYPE_UNION:
return "rcv._tab.Union";
return "rcv.Union";
case BASE_TYPE_VECTOR:
return GenGetter(type.VectorType());
default:
return "rcv._tab.Get" + namer_.Function(GenTypeBasic(type));
return "rcv.Get" + namer_.Function(GenTypeBasic(type));
}
}

Expand Down
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