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(Naga) Implement OpSpecConstantOp for the SPIR-V frontend
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‎CHANGELOG.md‎

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@@ -54,6 +54,12 @@ This is a breaking change
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By @R-Cramer4 in [#8230](https://github.com/gfx-rs/wgpu/pull/8230)
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### Changes
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#### naga
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- The SPIR-V frontend implements OpSpecConstantOp. By @hasenbanck in [8308](https://github.com/gfx-rs/wgpu/pull/8308).
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## v27.0.2 (2025-10-03)
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### Bug Fixes

‎naga/src/front/spv/error.rs‎

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@@ -26,6 +26,10 @@ pub enum Error {
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UnknownCapability(spirv::Word),
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#[error("unsupported instruction {1:?} at {0:?}")]
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UnsupportedInstruction(ModuleState, spirv::Op),
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#[error("unsupported opcode in specialization constant operation {0:?}")]
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UnsupportedSpecConstantOp(spirv::Op),
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#[error("invalid opcode in specialization constant operation {0:?}")]
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InvalidSpecConstantOp(spirv::Op),
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#[error("unsupported capability {0:?}")]
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UnsupportedCapability(spirv::Capability),
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#[error("unsupported extension {0}")]

‎naga/src/front/spv/mod.rs‎

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@@ -4803,6 +4803,7 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
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Op::ConstantFalse | Op::SpecConstantFalse => {
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self.parse_bool_constant(inst, false, &mut module)
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}
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Op::SpecConstantOp => self.parse_spec_constant_op(inst, &mut module),
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Op::Variable => self.parse_global_variable(inst, &mut module),
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Op::Function => {
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self.switch(ModuleState::Function, inst.op)?;
@@ -5899,6 +5900,296 @@ impl<I: Iterator<Item = u32>> Frontend<I> {
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self.insert_parsed_constant(module, id, type_id, ty, init, span)
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}
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fn parse_spec_constant_op(
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&mut self,
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inst: Instruction,
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module: &mut crate::Module,
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) -> Result<(), Error> {
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use spirv::Op;
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let start = self.data_offset;
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self.switch(ModuleState::Type, inst.op)?;
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inst.expect_at_least(4)?;
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let result_type_id = self.next()?;
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let result_id = self.next()?;
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let opcode_word = self.next()?;
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let type_lookup = self.lookup_type.lookup(result_type_id)?;
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let ty = type_lookup.handle;
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let span = self.span_from_with_op(start);
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let opcode = Op::from_u32(opcode_word).ok_or(Error::UnsupportedInstruction(
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self.state,
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Op::SpecConstantOp,
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))?;
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let mut get_const_expr =
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|frontend: &Self, const_id: spirv::Word| -> Result<Handle<crate::Expression>, Error> {
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let lookup = frontend.lookup_constant.lookup(const_id)?;
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match lookup.inner {
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// Wrap regular constants in overrides to avoid creating Expression::Constant
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// nodes, which would mark the entire expression tree as Const and fail
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// validation for complex operations (Binary, As, Math) in override
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// initializers.
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//
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// The downside is, that unused intermediate constants will get created, which
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// I would like to avoid.
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Constant::Constant(const_handle) => {
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let const_init = module.constants[const_handle].init;
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let const_ty = module.constants[const_handle].ty;
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let wrapper_override = crate::Override {
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name: Some(format!("_spec_const_op_const_{const_id}")),
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id: None,
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ty: const_ty,
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init: Some(const_init),
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};
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let override_handle = module.overrides.append(wrapper_override, span);
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Ok(module
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.global_expressions
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.append(crate::Expression::Override(override_handle), span))
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}
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Constant::Override(_) => Ok(module
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.global_expressions
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.append(lookup.inner.to_expr(), span)),
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}
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};
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let init = match opcode {
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Op::SConvert | Op::UConvert | Op::FConvert => {
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let value_id = self.next()?;
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let value_expr = get_const_expr(self, value_id)?;
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let scalar = match module.types[ty].inner {
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crate::TypeInner::Scalar(scalar)
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| crate::TypeInner::Vector { scalar, .. }
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| crate::TypeInner::Matrix { scalar, .. } => scalar,
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_ => return Err(Error::InvalidAsType(ty)),
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};
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module.global_expressions.append(
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crate::Expression::As {
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expr: value_expr,
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kind: scalar.kind,
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convert: Some(scalar.width),
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},
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span,
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)
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}
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Op::SNegate | Op::Not | Op::LogicalNot => {
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let value_id = self.next()?;
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let value_expr = get_const_expr(self, value_id)?;
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let op = match opcode {
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Op::SNegate => crate::UnaryOperator::Negate,
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Op::Not => crate::UnaryOperator::BitwiseNot,
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Op::LogicalNot => crate::UnaryOperator::LogicalNot,
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_ => unreachable!(),
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};
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module.global_expressions.append(
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crate::Expression::Unary {
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op,
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expr: value_expr,
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},
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span,
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)
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}
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Op::IAdd
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| Op::ISub
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| Op::IMul
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| Op::UDiv
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| Op::SDiv
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| Op::SRem
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| Op::UMod
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| Op::BitwiseOr
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| Op::BitwiseXor
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| Op::BitwiseAnd
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| Op::ShiftLeftLogical
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| Op::ShiftRightLogical
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| Op::ShiftRightArithmetic
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| Op::LogicalOr
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| Op::LogicalAnd
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| Op::LogicalEqual
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| Op::LogicalNotEqual
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| Op::IEqual
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| Op::INotEqual
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| Op::ULessThan
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| Op::SLessThan
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| Op::UGreaterThan
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| Op::SGreaterThan
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| Op::ULessThanEqual
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| Op::SLessThanEqual
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| Op::UGreaterThanEqual
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| Op::SGreaterThanEqual => {
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let left_id = self.next()?;
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let right_id = self.next()?;
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let left_expr = get_const_expr(self, left_id)?;
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let right_expr = get_const_expr(self, right_id)?;
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6032+
let op = match opcode {
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Op::IAdd => crate::BinaryOperator::Add,
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Op::ISub => crate::BinaryOperator::Subtract,
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Op::IMul => crate::BinaryOperator::Multiply,
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Op::UDiv | Op::SDiv => crate::BinaryOperator::Divide,
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Op::SRem | Op::UMod => crate::BinaryOperator::Modulo,
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Op::BitwiseOr => crate::BinaryOperator::InclusiveOr,
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Op::BitwiseXor => crate::BinaryOperator::ExclusiveOr,
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Op::BitwiseAnd => crate::BinaryOperator::And,
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Op::ShiftLeftLogical => crate::BinaryOperator::ShiftLeft,
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Op::ShiftRightLogical | Op::ShiftRightArithmetic => {
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crate::BinaryOperator::ShiftRight
6044+
}
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Op::LogicalOr => crate::BinaryOperator::LogicalOr,
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Op::LogicalAnd => crate::BinaryOperator::LogicalAnd,
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Op::LogicalEqual => crate::BinaryOperator::Equal,
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Op::LogicalNotEqual => crate::BinaryOperator::NotEqual,
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Op::IEqual => crate::BinaryOperator::Equal,
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Op::INotEqual => crate::BinaryOperator::NotEqual,
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Op::ULessThan | Op::SLessThan => crate::BinaryOperator::Less,
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Op::UGreaterThan | Op::SGreaterThan => crate::BinaryOperator::Greater,
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Op::ULessThanEqual | Op::SLessThanEqual => crate::BinaryOperator::LessEqual,
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Op::UGreaterThanEqual | Op::SGreaterThanEqual => {
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crate::BinaryOperator::GreaterEqual
6056+
}
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_ => unreachable!(),
6058+
};
6059+
6060+
module.global_expressions.append(
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crate::Expression::Binary {
6062+
op,
6063+
left: left_expr,
6064+
right: right_expr,
6065+
},
6066+
span,
6067+
)
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}
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6070+
Op::SMod => {
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// x - y * int(floor(float(x) / float(y)))
6072+
6073+
let left_id = self.next()?;
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let right_id = self.next()?;
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let left = get_const_expr(self, left_id)?;
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let right = get_const_expr(self, right_id)?;
6077+
6078+
let scalar = match module.types[ty].inner {
6079+
crate::TypeInner::Scalar(scalar) => scalar,
6080+
crate::TypeInner::Vector { scalar, .. } => scalar,
6081+
_ => return Err(Error::InvalidAsType(ty)),
6082+
};
6083+
6084+
let left_cast = module.global_expressions.append(
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crate::Expression::As {
6086+
expr: left,
6087+
kind: crate::ScalarKind::Float,
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convert: Some(scalar.width),
6089+
},
6090+
span,
6091+
);
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let right_cast = module.global_expressions.append(
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crate::Expression::As {
6094+
expr: right,
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kind: crate::ScalarKind::Float,
6096+
convert: Some(scalar.width),
6097+
},
6098+
span,
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);
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let div = module.global_expressions.append(
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crate::Expression::Binary {
6102+
op: crate::BinaryOperator::Divide,
6103+
left: left_cast,
6104+
right: right_cast,
6105+
},
6106+
span,
6107+
);
6108+
let floor = module.global_expressions.append(
6109+
crate::Expression::Math {
6110+
fun: crate::MathFunction::Floor,
6111+
arg: div,
6112+
arg1: None,
6113+
arg2: None,
6114+
arg3: None,
6115+
},
6116+
span,
6117+
);
6118+
let cast = module.global_expressions.append(
6119+
crate::Expression::As {
6120+
expr: floor,
6121+
kind: scalar.kind,
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convert: Some(scalar.width),
6123+
},
6124+
span,
6125+
);
6126+
let mult = module.global_expressions.append(
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crate::Expression::Binary {
6128+
op: crate::BinaryOperator::Multiply,
6129+
left: cast,
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right,
6131+
},
6132+
span,
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);
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module.global_expressions.append(
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crate::Expression::Binary {
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op: crate::BinaryOperator::Subtract,
6137+
left,
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right: mult,
6139+
},
6140+
span,
6141+
)
6142+
}
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6144+
Op::Select => {
6145+
let condition_id = self.next()?;
6146+
let o1_id = self.next()?;
6147+
let o2_id = self.next()?;
6148+
6149+
let cond = get_const_expr(self, condition_id)?;
6150+
let o1 = get_const_expr(self, o1_id)?;
6151+
let o2 = get_const_expr(self, o2_id)?;
6152+
6153+
module.global_expressions.append(
6154+
crate::Expression::Select {
6155+
condition: cond,
6156+
accept: o1,
6157+
reject: o2,
6158+
},
6159+
span,
6160+
)
6161+
}
6162+
6163+
Op::VectorShuffle | Op::CompositeExtract | Op::CompositeInsert | Op::QuantizeToF16 => {
6164+
// Nothing stops us from implementing these cases in general.
6165+
// I just couldn't get them to work properly.
6166+
return Err(Error::UnsupportedSpecConstantOp(opcode));
6167+
}
6168+
6169+
_ => return Err(Error::InvalidSpecConstantOp(opcode)),
6170+
};
6171+
6172+
// IMPORTANT: Overrides must have either a name or an id to be processed correctly
6173+
// by process_overrides(). OpSpecConstantOp results don't have a SpecId (they're
6174+
// not user-overridable), so we assign them a name based on the result_id.
6175+
let op_override = crate::Override {
6176+
name: Some(format!("_spec_const_op_{result_id}")),
6177+
id: None,
6178+
ty,
6179+
init: Some(init),
6180+
};
6181+
6182+
self.lookup_constant.insert(
6183+
result_id,
6184+
LookupConstant {
6185+
inner: Constant::Override(module.overrides.append(op_override, span)),
6186+
type_id: result_type_id,
6187+
},
6188+
);
6189+
6190+
Ok(())
6191+
}
6192+
59026193
fn insert_parsed_constant(
59036194
&mut self,
59046195
module: &mut crate::Module,

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