digitalmars.D.bugs - [Issue 3822] New: alloca() can return the same address inside a function
- d-bugmail puremagic.com (25/25) Feb 18 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3822
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- d-bugmail puremagic.com (13/13) Jun 26 2010 http://d.puremagic.com/issues/show_bug.cgi?id=3822
- d-bugmail puremagic.com (16/16) Feb 10 2012 http://d.puremagic.com/issues/show_bug.cgi?id=3822
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- d-bugmail puremagic.com (9/9) Feb 18 2012 http://d.puremagic.com/issues/show_bug.cgi?id=3822
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http://d.puremagic.com/issues/show_bug.cgi?id=3822
Summary: alloca() can return the same address inside a function
Product: D
Version: 2.040
Platform: Other
OS/Version: Windows
Status: NEW
Severity: normal
Priority: P2
Component: druntime
AssignedTo: sean invisibleduck.org
ReportedBy: bearophile_hugs eml.cc
import std.stdio: printf;
import std.c.stdlib: alloca;
void main() {
const int n = 8;
for (int i; i < 2; i++)
printf("%p\n", alloca(n));
}
It prints two times the same address, I don't know why, I think this can be
wrong.
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Feb 18 2010
d-bugmail puremagic.com
http://d.puremagic.com/issues/show_bug.cgi?id=3822
BCS <shro8822 vandals.uidaho.edu> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |shro8822 vandals.uidaho.edu
---
I've never used alloca so I'm not sure, so this is a guess:
alloca does stack allocation and the body of the for statement forms a scope on
the stack (this in this case contains no named variables). I'm guessing that
when that scope is exited, the allocation automatically gets deallocated.
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Feb 18 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3822I've never used alloca so I'm not sure, so this is a guess: alloca does stack allocation and the body of the for statement forms a scope on the stack (this in this case contains no named variables). I'm guessing that when that scope is exited, the allocation automatically gets deallocated.You can be right, thank you. Then it's very good for Phobos docs to say that alloca is relative to a scope and not to a function. The description of alloca() that I have seen says: The alloca() function allocates space in the stack frame of the caller, and returns a pointer to the allocated block. This temporary space is automatically freed when the function from which alloca() is called returns. While if you are right D alloca frees space when the scope of alloca ends and not when the function ends. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 18 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3822 Maybe the alloca() used by dmd frees memory as soon as the current scope is left, instead of deferring all deallocation until function exit. See: http://compilers.iecc.com/comparch/article/91-12-079 D documentation has to explain how exactly its alloca() works. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jun 07 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3822
nfxjfg gmail.com changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
CC| |nfxjfg gmail.com
Summary|alloca() can return the |Memory allocated with
|same address inside a |alloca() is freed at end of
|function |scope instead at end of
| |function
C code that compiles in D without modification should work exactly as it does
in C.
This means this is a rather bad code gen bug.
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Jun 07 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3822
nfxjfg gmail.com changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |critical
There's D code in druntime that assumes memory allocated by alloca() is valid
until the end of the function:
http://dsource.org/projects/druntime/browser/trunk/src/rt/adi.d#L242
Maybe the codegen for alloca() within loops is broken, or something.
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Jun 26 2010
http://d.puremagic.com/issues/show_bug.cgi?id=3822
yebblies <yebblies gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |yebblies gmail.com
Platform|Other |All
Version|2.040 |D1 & D2
AssignedTo|nobody puremagic.com |yebblies gmail.com
OS/Version|Windows |All
The issue here is that n is a compile-time constant, so the call to alloca is
optimized away completely, and always reserving the extra space. This
optimization is not valid if the call to alloca might be repeated.
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Feb 10 2012
http://d.puremagic.com/issues/show_bug.cgi?id=3822
yebblies <yebblies gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |pull
Summary|Memory allocated with |Invalid optimization of
|alloca() is freed at end of |alloca called with constant
|scope instead at end of |size
|function |
https://github.com/D-Programming-Language/dmd/pull/707
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Feb 10 2012
http://d.puremagic.com/issues/show_bug.cgi?id=3822https://github.com/D-Programming-Language/dmd/pull/707Thank you for your patch, yebblies! -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 11 2012
http://d.puremagic.com/issues/show_bug.cgi?id=3822Thank you for your patch, yebblies!You're welcome. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 11 2012
http://d.puremagic.com/issues/show_bug.cgi?id=3822 Commit pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/3fc9ee7064c05d4c8db6f1aac0a8896caa954e44 Issue 3822 - Invalid optimization of alloca called with constant size -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 18 2012
http://d.puremagic.com/issues/show_bug.cgi?id=3822 Commit pushed to dmd-1.x at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/c492323b6edc44a2bac4ea0edaed1e757854b9d0 fix Issue 3822 - Invalid optimization of alloca called with constant size -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Feb 18 2012
http://d.puremagic.com/issues/show_bug.cgi?id=3822
Walter Bright <bugzilla digitalmars.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |bugzilla digitalmars.com
Resolution| |FIXED
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Feb 18 2012