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Bytecode parity by youknowone · Pull Request #7535 · RustPython/RustPython · GitHub

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Bytecode parity #7535

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youknowone merged 4 commits into from
Mar 30, 2026
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Bytecode parity #7535

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4959703
Add CFG block splitting, jump threading, backward jump normalization,…
youknowone Mar 29, 2026
385b719
Add ConstantData::Slice and constant slice folding
youknowone Mar 30, 2026
f8927e1
Add ConstantData::Frozenset variant (type only, folding deferred)
youknowone Mar 30, 2026
42b24cb
Add duplicate_exits_without_lineno (disabled) and Block: Clone
youknowone Mar 30, 2026
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80 changes: 80 additions & 0 deletions crates/codegen/src/compile.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7574,6 +7574,11 @@ impl Compiler {
ast::Expr::Slice(ast::ExprSlice {
lower, upper, step, ..
}) => {
// Try constant slice folding first
if self.try_fold_constant_slice(lower.as_deref(), upper.as_deref(), step.as_deref())
{
return Ok(());
}
Comment on lines +7577 to +7581

coderabbitai Bot Mar 30, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

⚠️ Potential issue | 🟠 Major

try_fold_constant_slice is narrower than the rest of the compiler’s constant logic.

Lines 8999-9016 only fold numbers, booleans, and None, and Line 9005 also limits integer folding to i64. But ExprExt::is_constant_slice() already treats string/bytes/ellipsis bounds as constant, so cases like obj["a":"z"] skip the BINARY_SLICE fast path and still never reach the new LOAD_CONST(slice) path. Large integer literals have the same gap. That leaves valid constant slices on the old bytecode path and misses the parity target for this feature.

💡 Suggested fix 
-                if self.try_fold_constant_slice(lower.as_deref(), upper.as_deref(), step.as_deref())
-                {
+                if self.try_fold_constant_slice(
+                    lower.as_deref(),
+                    upper.as_deref(),
+                    step.as_deref(),
+                )? {
                     return Ok(());
                 }
-    fn try_fold_constant_slice(
-        &mut self,
-        lower: Option<&ast::Expr>,
-        upper: Option<&ast::Expr>,
-        step: Option<&ast::Expr>,
-    ) -> bool {
-        fn to_const(expr: Option<&ast::Expr>) -> Option<ConstantData> {
-            match expr {
-                None | Some(ast::Expr::NoneLiteral(_)) => Some(ConstantData::None),
-                Some(ast::Expr::NumberLiteral(ast::ExprNumberLiteral { value, .. })) => match value
-                {
-                    ast::Number::Int(i) => Some(ConstantData::Integer {
-                        value: i.as_i64()?.into(),
-                    }),
-                    ast::Number::Float(f) => Some(ConstantData::Float { value: *f }),
-                    ast::Number::Complex { real, imag } => Some(ConstantData::Complex {
-                        value: num_complex::Complex64::new(*real, *imag),
-                    }),
-                },
-                Some(ast::Expr::BooleanLiteral(ast::ExprBooleanLiteral { value, .. })) => {
-                    Some(ConstantData::Boolean { value: *value })
-                }
-                // Only match Constant_kind nodes (no UnaryOp)
-                _ => None,
-            }
-        }
+    fn try_fold_constant_slice(
+        &mut self,
+        lower: Option<&ast::Expr>,
+        upper: Option<&ast::Expr>,
+        step: Option<&ast::Expr>,
+    ) -> CompileResult<bool> {
+        let mut to_const = |expr: Option<&ast::Expr>| -> CompileResult<Option<ConstantData>> {
+            Ok(match expr {
+                None | Some(ast::Expr::NoneLiteral(_)) => Some(ConstantData::None),
+                Some(ast::Expr::NumberLiteral(ast::ExprNumberLiteral { value, .. })) => {
+                    Some(match value {
+                        ast::Number::Int(i) => ConstantData::Integer {
+                            value: ruff_int_to_bigint(i).map_err(|e| self.error(e))?,
+                        },
+                        ast::Number::Float(f) => ConstantData::Float { value: *f },
+                        ast::Number::Complex { real, imag } => ConstantData::Complex {
+                            value: Complex::new(*real, *imag),
+                        },
+                    })
+                }
+                Some(ast::Expr::StringLiteral(s)) => Some(ConstantData::Str {
+                    value: self.compile_string_value(s),
+                }),
+                Some(ast::Expr::BytesLiteral(b)) => Some(ConstantData::Bytes {
+                    value: b.value.bytes().collect(),
+                }),
+                Some(ast::Expr::BooleanLiteral(ast::ExprBooleanLiteral { value, .. })) => {
+                    Some(ConstantData::Boolean { value: *value })
+                }
+                Some(ast::Expr::EllipsisLiteral(_)) => Some(ConstantData::Ellipsis),
+                _ => None,
+            })
+        };
 
-        let (Some(start), Some(stop), Some(step_val)) =
-            (to_const(lower), to_const(upper), to_const(step))
+        let (Some(start), Some(stop), Some(step_val)) =
+            (to_const(lower)?, to_const(upper)?, to_const(step)?)
         else {
-            return false;
+            return Ok(false);
         };
 
         self.emit_load_const(ConstantData::Slice {
             elements: Box::new([start, stop, step_val]),
         });
-        true
+        Ok(true)
     }

Also applies to: 8992-9030

🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@crates/codegen/src/compile.rs` around lines 7577 - 7581,
try_fold_constant_slice currently only recognizes numbers, booleans and None and
limits integer folding to i64, which is narrower than
ExprExt::is_constant_slice; update try_fold_constant_slice to accept the same
constant kinds that ExprExt::is_constant_slice treats constant (include
string/bytes/ellipsis bounds and arbitrary-size integers, not just i64) so that
patterns like obj["a":"z"] and large integer literals are folded to
LOAD_CONST(slice) and hit the BINARY_SLICE fast path; make the same expansion in
the adjacent constant-folding block that has the i64 restriction so both places
have parity with ExprExt::is_constant_slice.

let mut compile_bound = |bound: Option<&ast::Expr>| match bound {
Some(exp) => self.compile_expression(exp),
None => {
Expand Down Expand Up @@ -8407,6 +8412,24 @@ impl Compiler {
let arg0 = self.varname(".0")?;

let return_none = init_collection.is_none();

// PEP 479: Wrap generator/coroutine body with StopIteration handler
let is_gen_scope = self.current_symbol_table().is_generator || is_async;
let stop_iteration_block = if is_gen_scope {
let handler_block = self.new_block();
emit!(
self,
PseudoInstruction::SetupCleanup {
delta: handler_block
}
);
self.set_no_location();
self.push_fblock(FBlockType::StopIteration, handler_block, handler_block)?;
Some(handler_block)
} else {
None
};

// Create empty object of proper type:
if let Some(init_collection) = init_collection {
self._emit(init_collection, OpArg::new(0), BlockIdx::NULL)
Expand Down Expand Up @@ -8496,6 +8519,23 @@ impl Compiler {

self.emit_return_value();

// Close StopIteration handler and emit handler code
if let Some(handler_block) = stop_iteration_block {
emit!(self, PseudoInstruction::PopBlock);
self.set_no_location();
self.pop_fblock(FBlockType::StopIteration);
self.switch_to_block(handler_block);
emit!(
self,
Instruction::CallIntrinsic1 {
func: oparg::IntrinsicFunction1::StopIterationError
}
);
self.set_no_location();
emit!(self, Instruction::Reraise { depth: 1u32 });
self.set_no_location();
}

let code = self.exit_scope();

self.ctx = prev_ctx;
Expand Down Expand Up @@ -8949,6 +8989,46 @@ impl Compiler {
self.emit_arg(idx, |consti| Instruction::LoadConst { consti })
}

/// Fold constant slice: if all parts are compile-time constants, emit LOAD_CONST(slice).
fn try_fold_constant_slice(
&mut self,
lower: Option<&ast::Expr>,
upper: Option<&ast::Expr>,
step: Option<&ast::Expr>,
) -> bool {
fn to_const(expr: Option<&ast::Expr>) -> Option<ConstantData> {
match expr {
None | Some(ast::Expr::NoneLiteral(_)) => Some(ConstantData::None),
Some(ast::Expr::NumberLiteral(ast::ExprNumberLiteral { value, .. })) => match value
{
ast::Number::Int(i) => Some(ConstantData::Integer {
value: i.as_i64()?.into(),
}),
ast::Number::Float(f) => Some(ConstantData::Float { value: *f }),
ast::Number::Complex { real, imag } => Some(ConstantData::Complex {
value: num_complex::Complex64::new(*real, *imag),
}),
},
Some(ast::Expr::BooleanLiteral(ast::ExprBooleanLiteral { value, .. })) => {
Some(ConstantData::Boolean { value: *value })
}
// Only match Constant_kind nodes (no UnaryOp)
_ => None,
}
}

let (Some(start), Some(stop), Some(step_val)) =
(to_const(lower), to_const(upper), to_const(step))
else {
return false;
};

self.emit_load_const(ConstantData::Slice {
elements: Box::new([start, stop, step_val]),
});
true
}

fn emit_return_const(&mut self, constant: ConstantData) {
self.emit_load_const(constant);
emit!(self, Instruction::ReturnValue)
Expand Down
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