interpreter: lower && and || as short-circuit branches#73
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Lower logical AND/OR at codegen time using Branch and Jump instead of dedicated And/Or VM instructions. Results are coerced to integer truth values (0 or 1), matching gawk mkbool() behavior. Closes uutils#69
Alonely0
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Jul 10, 2026
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Quite nice. The only thing I'd say is that the two helpers are unnecessarily complex (see the other review comment).
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| fn lower_and_into(&mut self, lhs: &Expr<'_>, rhs: &Expr<'_>, dest: Reg) { | ||
| let lhs_reg = self.alloc_reg(); | ||
| self.lower_expr_into(lhs, *lhs_reg); | ||
| let br = self.bc.emit(Instruction::br(*lhs_reg, Label(0))); | ||
| let false_label = self.following_instr(0); | ||
| self.bc.nth(br).set_label(false_label); | ||
| self.free_reg(lhs_reg); | ||
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| self.bc | ||
| .emit(Instruction::Copy { dest, arg: Arg { imm: 0 }, ty: ArgTy::Imm }); | ||
| let jmp = self.bc.emit(Instruction::Jump { to: Label(0) }); | ||
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| let true_label = self.following_instr(0); | ||
| self.bc.nth(br).set_then_label(true_label); | ||
| let rhs_reg = self.alloc_reg(); | ||
| self.lower_expr_into(rhs, *rhs_reg); | ||
| self.truthify(*rhs_reg, dest); | ||
| self.free_reg(rhs_reg); | ||
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| let end = self.following_instr(0); | ||
| self.bc.nth(jmp).set_label(end); | ||
| } |
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Pretty sure we can use the helpers like emit_branch, emit_jump to make this shorter and more robust, right?
Something like:
fn lower_and_into(&mut self, lhs: &Expr<'_>, rhs: &Expr<'_>, dest: Reg) {
let (if_label, _) = self.emit_branch(lhs, |this| {
let rhs_reg = this.alloc_reg();
this.lower_expr_into(rhs, *rhs_reg);
this.truthify(*rhs_reg, dest);
this.free_reg(rhs_reg);
});
self.bc.nth(if_label).push_end_label();
self.emit_jump(|this| {
this.bc
.emit(Instruction::Copy { dest, arg: Arg { imm: 0 }, ty: ArgTy::Imm });
});
}| self.bc.nth(jmp).set_label(end); | ||
| } | ||
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| fn lower_or_into(&mut self, lhs: &Expr<'_>, rhs: &Expr<'_>, dest: Reg) { |
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| self.bc | ||
| .emit(Instruction::Negation { dest: *tmp, arg: Arg { reg: src }, ty: ArgTy::Reg }); | ||
| self.bc | ||
| .emit(Instruction::Negation { dest, arg: Arg { reg: *tmp }, ty: ArgTy::Reg }); |
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As a former pythonist, this amuses me to no end. IYKYK.
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Lower logical AND/OR at codegen time using Branch and Jump instead of dedicated And/Or VM instructions. Results are coerced to integer truth values (0 or 1), matching gawk mkbool() behavior.
Closes #69