OperandExceeded when using specialization constants in work group size

[alixinne]

Context

Given the following GLSL compute shader which defines its work group size using specialization constant 0:

#version 460

layout(local_size_x_id = 0) in;

void main() {
    int kernelId = int(gl_WorkGroupSize.x);
}

Compiling it using shaderc result in the following (disassembled using spirv-dis) SPIR-V file:

; SPIR-V
; Version: 1.0
; Generator: Google Shaderc over Glslang; 7
; Bound: 17
; Schema: 0
               OpCapability Shader
          %1 = OpExtInstImport "GLSL.std.450"
               OpMemoryModel Logical GLSL450
               OpEntryPoint GLCompute %main "main"
               OpExecutionMode %main LocalSize 1 1 1
               OpSource GLSL 460
               OpSourceExtension "GL_GOOGLE_cpp_style_line_directive"
               OpSourceExtension "GL_GOOGLE_include_directive"
               OpName %main "main"
               OpName %kernelId "kernelId"
               OpDecorate %10 SpecId 0
               OpDecorate %gl_WorkGroupSize BuiltIn WorkgroupSize
       %void = OpTypeVoid
          %3 = OpTypeFunction %void
        %int = OpTypeInt 32 1
%_ptr_Function_int = OpTypePointer Function %int
       %uint = OpTypeInt 32 0
         %10 = OpSpecConstant %uint 1
     %uint_1 = OpConstant %uint 1
     %v3uint = OpTypeVector %uint 3
%gl_WorkGroupSize = OpSpecConstantComposite %v3uint %10 %uint_1 %uint_1
     %uint_0 = OpConstant %uint 0
         %15 = OpSpecConstantOp %uint CompositeExtract %gl_WorkGroupSize 0
         %16 = OpSpecConstantOp %int IAdd %15 %uint_0
       %main = OpFunction %void None %3
          %5 = OpLabel
   %kernelId = OpVariable %_ptr_Function_int Function
               OpStore %kernelId %16
               OpReturn
               OpFunctionEnd

Expected behavior

Parsing the module using rspirv succeeds.

Observed behavior

Trying to parse the resulting binary module with rspirv results in the following error:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: OperandExceeded(436, 23)', src/libcore/result.rs:1188:5
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.40/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:84
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1025
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1426
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:193
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:471
  11: rust_begin_unwind
             at src/libstd/panicking.rs:375
  12: core::panicking::panic_fmt
             at src/libcore/panicking.rs:84
  13: core::result::unwrap_failed
             at src/libcore/result.rs:1188
  14: core::result::Result<T,E>::unwrap
             at /rustc/5e1a799842ba6ed4a57e91f7ab9435947482f7d8/src/libcore/result.rs:956
  15: rspirv_bug::main
             at src/main.rs:6
  16: std::rt::lang_start::{{closure}}
             at /rustc/5e1a799842ba6ed4a57e91f7ab9435947482f7d8/src/libstd/rt.rs:67
  17: std::rt::lang_start_internal::{{closure}}
             at src/libstd/rt.rs:52
  18: std::panicking::try::do_call
             at src/libstd/panicking.rs:292
  19: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:78
  20: std::panicking::try
             at src/libstd/panicking.rs:270
  21: std::panic::catch_unwind
             at src/libstd/panic.rs:394
  22: std::rt::lang_start_internal
             at src/libstd/rt.rs:51
  23: std::rt::lang_start
             at /rustc/5e1a799842ba6ed4a57e91f7ab9435947482f7d8/src/libstd/rt.rs:67
  24: main
  25: __libc_start_main
  26: _start
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Affected versions

• Current state of the master branch (#3905855)
• Latest version published on crates.io (0.5.4)

How to reproduce the bug

See example code at https://github.com/vtavernier/rspirv-bug. Clone and use cargo run to check.

[Jasper-Bekkers]

@vtavernier Could you take a look at the PR and see if it fixes your issue? I think we were parsing OpSpecConstantOp incorrectly before.

[alixinne]

The PR indeed fixes the issue, thanks!