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digitalmars.D.bugs - [Issue 6733] New: DMD Crash (internal error)

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6733

           Summary: DMD Crash (internal error)
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: critical
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: wfunction hotmail.com



I have no idea what the heck is going on, but this crashes on DMD32 D Compiler
v2.055:

struct Zero { }
void test(T1, T2)(T1 a, T2 b) { }
void main() { test(Zero(), Zero()); }

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Sep 26 2011
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6733




Oh, and the error is:

Internal error: ..\ztc\cod2.c 4624

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Sep 26 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code
                 CC|                            |clugdbug yahoo.com.au
            Summary|DMD Crash (internal error)  |Regression(2.054)
                   |                            |ICE(cod2.c) struct literals
                   |                            |as template arguments
           Severity|critical                    |regression



This worked in 2.053 and earlier.

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Oct 21 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6733


Brad Roberts <braddr puremagic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |braddr puremagic.com



---
I just bisected it down to:

commit 4c9661fa9fbd427909a334133dfc7f3869e47c31
Author: Walter Bright <walter walterbright.com>
Date:   Thu Jun 23 00:50:46 2011 -0700

    nothrow inference

Reverting it from tip of master yields a successful build of the code above.

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Oct 21 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
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 I just bisected it down to:
 
 commit 4c9661fa9fbd427909a334133dfc7f3869e47c31
 Author: Walter Bright <walter walterbright.com>
 Date:   Thu Jun 23 00:50:46 2011 -0700
 
     nothrow inference
 
 Reverting it from tip of master yields a successful build of the code above.


Thanks. The backend failure is occuring inside a comma expression (x, y). Fails
because x isn't an expression, it's just a parameter (presumably the struct
literal).

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Oct 21 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Actually this is more a pseudo-regresssion, it's just an expansion of an
existing bug into a few more cases. Walter's commit has nothing to do with the
root cause. The test case below fails in exactly the same way on 2.025 (but
passed on 2.023).

struct Zero { int x; }
void test(T)(T a, T b) pure nothrow { } 
void main() { test(Zero(7), Zero(4)); }

The bug is triggered when test() gets completely optimized away because it's
pure nothrow.

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Oct 21 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6733




Reduced test case:

void bug6733(int a, int b) pure nothrow { } 
void main() {
   int z;
   bug6733(z++, z++);
}

This is definitely a backend bug. What happens is, that since it's pure nothrow
and the result is unused, it's a no-side-effect call (OPcallns).
In the first optimisation step (optelem in cgelem.c), the call gets discarded,
and simply replaced with the parameter list (wrapped in an OPparam). If the
parameters had no side-effects, the whole thing would be discarded.
If there's only one with a side-effect, it's the only thing that's left. But if
there are TWO with side-effects, the OPparam remains.
The rest of the backend can't cope with a naked OPparam. Boom.
Solution would be to replace the OPparam with comma expressions.

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Oct 21 2011
prev sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |FIXED



02:53:28 PDT ---
https://github.com/D-Programming-Language/dmd/commit/6536012f7e23d5dc5928567224d47cc7d9997ceb

https://github.com/D-Programming-Language/dmd/commit/ab50833d7ca7fde0380525ed11e66908c440667a

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Oct 22 2011