Dart SDK build fails in DebugSIMRISCV32 mode on dart-fuzz bot

[alexmarkov]

FAILED: gen/dds_aot.dart.snapshot 
python3 ../../build/gn_run_binary.py compiled_action gen_snapshot --deterministic --snapshot-kind=app-aot-elf --elf=/b/s/w/ir/cache/builder/sdk/out/DebugSIMRISCV32/gen/dds_aot.dart.snapshot /b/s/w/ir/cache/builder/sdk/out/DebugSIMRISCV32/gen/utils/dds/generate_dds_aot_snapshot.dart.dill
Command failed: /b/s/w/ir/cache/builder/sdk/out/DebugSIMRISCV32/gen_snapshot --deterministic --snapshot-kind=app-aot-elf --elf=/b/s/w/ir/cache/builder/sdk/out/DebugSIMRISCV32/gen/dds_aot.dart.snapshot /b/s/w/ir/cache/builder/sdk/out/DebugSIMRISCV32/gen/utils/dds/generate_dds_aot_snapshot.dart.dill
output: ../../runtime/vm/compiler/backend/il_riscv.cc: 839: error: expected: !is_unboxed_int || RepresentationUtils::ValueSize(representation()) <= compiler::target::kWordSize
version=3.3.0-edge.6bca7060de9e502ce861127c04324a9d77042df9 (main) (Wed Dec 20 01:55:58 2023 +0000) on "linux_simriscv32"
pid=278900, thread=278900, isolate_group=isolate(0x58e7d9e0), isolate=(nil)((nil))
os=linux, arch=riscv32, comp=no, sim=yes
isolate_instructions=0, vm_instructions=0
fp=ff929408, sp=ff929374, pc=56c0b3db
  pc 0x56c0b3db fp 0xff929408 dart::Profiler::DumpStackTrace+0x9b
  pc 0x572701a1 fp 0xff929428 Dart_DumpNativeStackTrace+0x21
  pc 0x56916226 fp 0xff929458 dart::Assert::Fail+0x36
  pc 0x570dcaa5 fp 0xff9294a8 dart::UnboxedConstantInstr::MakeLocationSummary+0x195
  pc 0x5712d8b9 fp 0xff929528 dart::SSALivenessAnalysis::ComputeInitialSets+0x4e9
  pc 0x57073c7e fp 0xff929578 dart::LivenessAnalysis::Analyze+0x20e
  pc 0x5713ba0e fp 0xff9295d8 dart::FlowGraphAllocator::AllocateRegisters+0x2e
  pc 0x5718b73f fp 0xff9298b8 dart::CompilerPass_AllocateRegisters::DoBody+0x5f
  pc 0x57189b4a fp 0xff929958 dart::CompilerPass::Run+0x13a
  pc 0x5718a369 fp 0xff929998 dart::CompilerPass::RunPipeline+0x369
  pc 0x57023d34 fp 0xff929dc8 dart::PrecompileParsedFunctionHelper::Compile+0x664
  pc 0x57024c2d fp 0xff92a338 dart::PrecompileFunctionHelper+0x3cd
  pc 0x5701ec8f fp 0xff92a3e8 dart::Precompiler::CompileFunction+0x1af
  pc 0x5702d10d fp 0xff92a438 dart::Precompiler::PrecompileConstructors+0xdd
  pc 0x56c1f90b fp 0xff92a478 dart::ProgramWalker::VisitFunction+0x4b
  pc 0x56c1c719 fp 0xff92a4b8 dart::ProgramWalker::VisitWorklist+0xa9
  pc 0x56c1c299 fp 0xff92a588 dart::ProgramVisitor::WalkProgram+0x4b9
  pc 0x57014f32 fp 0xff92a5f8 dart::Precompiler::PrecompileConstructors+0x82
  pc 0x57010beb fp 0xff92ac88 dart::Precompiler::DoCompileAll+0x3ab
  pc 0x5701079a fp 0xff92af88 dart::Precompiler::CompileAll+0xda
  pc 0x5726d3d9 fp 0xff92b078 Dart_Precompile+0x299
  pc 0x568e3009 fp 0xff92b188 dart::bin::main+0x979
  pc 0x568e3fa4 fp 0xff92b1b8 main+0x24
-- End of DumpStackTrace
=== Crash occurred when compiling dart:io__ExternalBuffer@14069316__ExternalBuffer@14069316. in AOT mode in AllocateRegisters pass
*** BEGIN CFG
AllocateRegisters
==== dart:io__ExternalBuffer@14069316__ExternalBuffer@14069316. (Constructor)
B0[graph]:0 {
      v0 <- Constant(#null) T{Null?}
      v22 <- UnboxedConstant(#1) int32
}
B1[function entry]:2 {
      v2 <- Parameter(0) T{_ExternalBuffer}
      v3 <- Parameter(1) [-9223372036854775808, 9223372036854775807] int64
}
    StoreField(v2 . size = v3 <int64>)
    v7 <- UnboxedConstant(#63) [63, 63] int64
    v8 <- ShiftInt64Op(>> [tr], v3, v7) [-1, 0] int64
    v9 <- UnboxedConstant(#1) [1, 1] int64
    v19 <- IntConverter(int64->int32, v8) int32
    v10 <- BinaryInt32Op(& [-o], v19 T{int}, v22 T{_Smi}) [0, 1] int32
    v21 <- IntConverter(int32->int64, v10 T{int}) int64
    v11 <- BinaryInt64Op(+ [tr], v3, v21 T{int}) [-9223372036854775808, 9223372036854775807] int64
    v5 <- ShiftInt64Op(>> [tr], v11, v9 T{_Smi}) [-4611686018427387904, 4611686018427387903] int64
    StoreField(v2 . start = v5 <int64>)
    StoreField(v2 . end = v5 T{int} <int64>)
    Return:20(v0)
*** END CFG

Full log: https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8761221808019191521/+/u/build_dart__riscv_/stdout

/cc @a-siva @rmacnak-google

[dcharkes]

When addressing this, don't forget to clean up TODO(https://dartbug.com/54434) in utils/dartdev/BUILD.gn.