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We had something hacked together to support `(ref.i31 (i32.const N))`. It wasn't a long-term solution. This is the first time that we have to really deal with multi-instruction const expressions. This commit introduces a tiny interpreter to evaluate const expressions.pull/8465/head
Nick Fitzgerald
7 months ago
committed by
GitHub
GitHub
17 changed files with 500 additions and 372 deletions
@ -0,0 +1,102 @@ |
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//! Evaluating const expressions.
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use crate::{Instance, VMGcRef, ValRaw, I31}; |
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use anyhow::{anyhow, bail, Result}; |
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use smallvec::SmallVec; |
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use wasmtime_environ::{ConstExpr, FuncIndex, GlobalIndex, Module}; |
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/// An interpreter for const expressions.
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///
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/// This can be reused across many const expression evaluations to reuse
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/// allocated resources, if any.
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#[derive(Default)] |
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pub struct ConstExprEvaluator { |
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stack: SmallVec<[ValRaw; 2]>, |
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} |
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/// The context within which a particular const expression is evaluated.
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pub struct ConstEvalContext<'a, 'b> { |
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instance: &'a mut Instance, |
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module: &'b Module, |
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} |
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impl<'a, 'b> ConstEvalContext<'a, 'b> { |
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/// Create a new context.
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pub fn new(instance: &'a mut Instance, module: &'b Module) -> Self { |
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Self { instance, module } |
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} |
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fn global_get(&mut self, index: GlobalIndex) -> Result<ValRaw> { |
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unsafe { |
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let gc_store = (*self.instance.store()).gc_store(); |
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let global = self |
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.instance |
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.defined_or_imported_global_ptr(index) |
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.as_ref() |
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.unwrap(); |
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Ok(global.to_val_raw(gc_store, self.module.globals[index].wasm_ty)) |
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} |
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} |
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fn ref_func(&mut self, index: FuncIndex) -> Result<ValRaw> { |
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Ok(ValRaw::funcref( |
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self.instance.get_func_ref(index).unwrap().cast(), |
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)) |
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} |
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} |
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impl ConstExprEvaluator { |
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/// Evaluate the given const expression in the given context.
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///
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/// # Unsafety
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///
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/// The given const expression must be valid within the given context,
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/// e.g. the const expression must be well-typed and the context must return
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/// global values of the expected types. This evaluator operates directly on
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/// untyped `ValRaw`s and does not and cannot check that its operands are of
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/// the correct type.
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pub unsafe fn eval( |
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&mut self, |
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context: &mut ConstEvalContext<'_, '_>, |
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expr: &ConstExpr, |
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) -> Result<ValRaw> { |
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self.stack.clear(); |
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for op in expr.ops() { |
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match op { |
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wasmtime_environ::ConstOp::I32Const(i) => self.stack.push(ValRaw::i32(*i)), |
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wasmtime_environ::ConstOp::I64Const(i) => self.stack.push(ValRaw::i64(*i)), |
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wasmtime_environ::ConstOp::F32Const(f) => self.stack.push(ValRaw::f32(*f)), |
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wasmtime_environ::ConstOp::F64Const(f) => self.stack.push(ValRaw::f64(*f)), |
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wasmtime_environ::ConstOp::V128Const(v) => self.stack.push(ValRaw::v128(*v)), |
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wasmtime_environ::ConstOp::GlobalGet(g) => self.stack.push(context.global_get(*g)?), |
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wasmtime_environ::ConstOp::RefNull => self.stack.push(ValRaw::null()), |
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wasmtime_environ::ConstOp::RefFunc(f) => self.stack.push(context.ref_func(*f)?), |
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wasmtime_environ::ConstOp::RefI31 => { |
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let i = self.pop()?.get_i32(); |
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let i31 = I31::wrapping_i32(i); |
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let raw = VMGcRef::from_i31(i31).as_raw_u32(); |
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self.stack.push(ValRaw::anyref(raw)); |
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} |
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} |
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} |
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if self.stack.len() == 1 { |
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Ok(self.stack[0]) |
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} else { |
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bail!( |
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"const expr evaluation error: expected 1 resulting value, found {}", |
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self.stack.len() |
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) |
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} |
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} |
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fn pop(&mut self) -> Result<ValRaw> { |
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self.stack.pop().ok_or_else(|| { |
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anyhow!( |
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"const expr evaluation error: attempted to pop from an empty \ |
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evaluation stack" |
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) |
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}) |
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} |
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} |
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@ -0,0 +1,31 @@ |
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(module $env |
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(global (export "g1") i32 (i32.const 42)) |
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(global (export "g2") i32 (i32.const 99)) |
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) |
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(register "env") |
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(module $i31ref_of_global_const_expr_and_tables |
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(global $g1 (import "env" "g1") i32) |
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(global $g2 (import "env" "g2") i32) |
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(table $t 3 3 (ref i31) (ref.i31 (global.get $g1))) |
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(elem (table $t) (i32.const 2) (ref i31) (ref.i31 (global.get $g2))) |
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(func (export "get") (param i32) (result i32) |
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(i31.get_u (local.get 0) (table.get $t)) |
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) |
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) |
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(assert_return (invoke "get" (i32.const 0)) (i32.const 42)) |
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(assert_return (invoke "get" (i32.const 1)) (i32.const 42)) |
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(assert_return (invoke "get" (i32.const 2)) (i32.const 99)) |
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(module $i31ref_of_global_const_expr_and_globals |
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(global $g1 (import "env" "g1") i32) |
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(global $g2 i31ref (ref.i31 (global.get $g1))) |
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(func (export "get") (result i32) |
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(i31.get_u (global.get $g2)) |
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) |
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) |
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(assert_return (invoke "get") (i32.const 42)) |
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