0006359: not merged equal pattern matching branches

View Issue Details [ Jump to Notes ]

[ Issue History ] [ Print ]

Project

Category

View Status

Date Submitted

Last Update

0006359

OCaml

back end (clambda to assembly)

public

2014-04-01 19:56

2015-12-11 19:26

Reporter

chambart

Assigned To

maranget

Priority

normal

Severity

minor

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

Target Version

Fixed in Version

4.02.0+dev

Summary

0006359: not merged equal pattern matching branches

Description

In the following example (extracted from ocamlnet), the fields extractions of n and g for cases `A and `D are not merged.

match `C with
| `A(n,g)
| `D(n,g) -> n + g
| _ -> 0

In the resulting lambda
# ocamlc -c -drawlambda example.ml
(setglobal Example!
  (seq
    (let (match/1012 67a)
      (catch
        (catch
          (if (isint match/1012) (exit 2)
            (let (variant/1019 (field 0 match/1012))
              (if (!= variant/1019 65)
                (if (!= variant/1019 68) (exit 2)
                  (let
                    (match/1017 (field 1 match/1012)
                     g/1016 (field 1 match/1017)
                     n/1015 (field 0 match/1017))
                    (exit 1 n/1015 g/1016)))
                (let
                  (match/1017 (field 1 match/1012)
                   g/1016 (field 1 match/1017)
                   n/1015 (field 0 match/1017))
                  (exit 1 n/1015 g/1016)))))
         with (2) 0)
       with (1 n/1008 g/1009) (+ n/1008 g/1009)))
    (makeblock 0)))

This is not strictly speaking a bug since it does not impact anything,
but I would like to assume that identifiers can't be bound multiple times
(in my backend patches) and this is the only case I know (in the opam
repository) where this don't hold.

Tags

No tags attached.

Attached Files

Relationships

Notes
(0011169) garrigue (manager) 2014-04-02 04:28	Multiple binding of the same identifier is a bug: there are already parts of the backend where this invariant is assumed, and I have generated wrong code by just breaking it. Whether to merge the branches or not is another question.

(0011171) maranget (manager) 2014-04-02 11:20	This is indeed a bug, and it is related to sharing! (The match compiler re-shares actions which are alpha-equivalent but this sharing is lost in the case for instance of variants. --Luc

(0011173) maranget (manager) 2014-04-02 15:24	Bug fixed in trunk. Thanks to all. --Luc

Issue History
Date Modified	Username	Field	Change
2014-04-01 19:56	chambart	New Issue
2014-04-02 04:28	garrigue	Note Added: 0011169
2014-04-02 11:20	maranget	Note Added: 0011171
2014-04-02 11:22	maranget	Assigned To	=> maranget
2014-04-02 11:22	maranget	Status	new => confirmed
2014-04-02 15:23	maranget	Status	confirmed => resolved
2014-04-02 15:23	maranget	Resolution	open => fixed
2014-04-02 15:23	maranget	Fixed in Version	=> 4.02.0+dev
2014-04-02 15:24	maranget	Note Added: 0011173
2015-12-11 19:26	xleroy	Status	resolved => closed
2017-02-23 16:35	doligez	Category	OCaml backend (code generation) => Back end (clambda to assembly)
2017-02-23 16:44	doligez	Category	Back end (clambda to assembly) => back end (clambda to assembly)