StackOverflow in the optimizer when trying to optimize an errorNode

[dlangBugzillaToGithub]

dlang reported this on 2018-11-19T18:01:54Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19413

CC List

• RazvanN
• Stefan Koch

Description

Tested on Windows DMD 2081.2 and 2083.0
On Linux 2.065.0 and 2082.0

Compiler segfaults when assigning from a slice to an AA that contains another array in CTFE.

Does not occur if executed at runtime or with a string[string].

---
void main() { enum a = d(); }

auto d() {
    alias VP = string[string];
    VP[string] values;
    string str = "aaaaaa";
    values[str]["s"] = "val";

    str = str[1..3];
    values[str]["s"] = "val"; // <-- right here.

    return values;
}
---
---
DMD v2.083.0

predefs   Have_new DigitalMars Windows CRuntime_DigitalMars CppRuntime_DigitalMars LittleEndian D_Version2 all D_InlineAsm D_InlineAsm_X86 X86 Win32 assert D_ModuleInfo D_Exceptions D_TypeInfo D_HardFloat
binary    C:\D\dmd2\windows\bin\dmd.exe
version   v2.083.0

config    C:\D\dmd2\windows\bin\sc.ini
DFLAGS    -IC:\D\dmd2\windows\bin\..\..\src\phobos -IC:\D\dmd2\windows\bin\..\..\src\druntime\import
---

[dlangBugzillaToGithub]

dlang (@Vild) commented on 2018-11-20T11:58:14Z

run.dlang.io runs this successfully from 2.061 to 2.080.1; it segfaults from 2.081.1 to current.

[dlangBugzillaToGithub]

razvan.nitu1305 commented on 2018-11-21T12:22:58Z

This is the output I get on run.dlang.io:

Up to      2.060  : Failure with output:
-----
onlineapp.d(4): Error: no identifier for declarator VP
onlineapp.d(4): Error: alias cannot have initializer
-----

Since      2.061  : Success and no output

Maybe close this as invalid?

[dlangBugzillaToGithub]

dlang (@Vild) commented on 2018-11-22T13:00:53Z

I'm sorry; I'd removed a writeln on run.dlang.io before posting it here but didn't test it. The writeln isn't necessary when I run it locally.

---
import std.stdio;

void main() { enum a = d(); writeln(a); }

auto d() {
    alias VP = string[string];
    VP[string] values;
    string str = "aaaaaa";
    values[str]["s"] = "val";

    str = str[1..3];
    values[str]["s"] = "val"; // <-- right here.

    return values;
}
---

[dlangBugzillaToGithub]

uplink.coder commented on 2018-11-22T14:49:36Z

This does not seem to be a CTFE issue.

It's a problem where the optimizer will try to optimise an invalid node.

Also there is no need to use writeln, you can replace the writeln by void use(A)(A a) {}

[dlangBugzillaToGithub]

uplink.coder commented on 2018-11-22T15:23:38Z

Some more information:

What happens is actually a stack-overflow in optimize.d:1209

I guess my guess is that error-nodes do compare false to all other nodes since an error node does make it through. the Optimizer can never verify that the fixed point has been reached.