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[Bug c++/14531] New: pessimise code, loose constantness
From: |
smelkov at mph1 dot phys dot spbu dot ru |
Subject: |
[Bug c++/14531] New: pessimise code, loose constantness |
Date: |
11 Mar 2004 12:47:49 -0000 |
I've found some case, where g++ fails to recognize an expression as compile
time const
(ok, it recognizes it, but delays initialization till program run)
Here is the case source with g++ and icc8 assember output. Just look on how
subidx_rmap is
initialized.
--- const_array.cpp ---
//! calculates offset of (unambigous, non-virtual) BASE in CHILD
//! @param TYPE class inhereted from BASE
//! @param BASE the base class for TYPE
//! @note it looks like C++ mandates NULL pointer to be always casted to
NULL, hence i
//! use 0x1000 here.
#define base_delta(TYPE, BASE) ( (signed long)((static_cast<BASE*>(
reinterpret_cast<TYPE*>(0x1000UL) ))) - 0x1000 )
struct A
{
int a;
};
struct B
{
int b;
};
struct C : public A, public B
{
};
const signed long subidx_rmap[] =
{
base_delta(C, B),
33,
137
};
---------------------------------
---const_array.s.g++----
.file "const_array.cpp"
.local subidx_rmap
.comm subidx_rmap,12,4
.text
.align 2
.type __static_initialization_and_destruction_0(int, int), @function
__static_initialization_and_destruction_0(int, int):
.LFB3:
pushl %ebp
.LCFI0:
movl %esp, %ebp
.LCFI1:
cmpl $65535, 12(%ebp)
jne .L1
cmpl $1, 8(%ebp)
jne .L1
movl $4, %eax
movl %eax, subidx_rmap
movl $33, subidx_rmap+4
movl $137, subidx_rmap+8
.L1:
popl %ebp
ret
.LFE3:
.size __static_initialization_and_destruction_0(int, int),
.-__static_initialization_and_destruction_0(int, int)
.align 2
.type _GLOBAL__I_const_array.cppG85Xva, @function
_GLOBAL__I_const_array.cppG85Xva:
.LFB5:
pushl %ebp
.LCFI2:
movl %esp, %ebp
.LCFI3:
subl $8, %esp
.LCFI4:
movl $65535, 4(%esp)
movl $1, (%esp)
call __static_initialization_and_destruction_0(int, int)
leave
ret
.LFE5:
.size _GLOBAL__I_const_array.cppG85Xva,
.-_GLOBAL__I_const_array.cppG85Xva
.section .ctors,"aw",@progbits
.align 4
.long _GLOBAL__I_const_array.cppG85Xva
.section .note.GNU-stack,"",@progbits
.ident "GCC: (GNU) 3.3.3"
--------------------------------
---const_array.s.icc---
# -- Machine type IA32
# mark_description "Intel(R) C++ Compiler for 32-bit applications, Version 8.0
Build
20031016Z %s";
# mark_description "-long_double -Wall -S -o const_array.s.icc";
.ident "Intel(R) C++ Compiler for 32-bit applications, Version 8.0
Build 20031016Z %s"
.ident "-long_double -Wall -S -o const_array.s.icc"
.file "const_array.cpp"
.text
.data
.align 4
.bss
.align 4
.section .rodata, "a"
.align 4
.section .data1, "wa"
.align 4
.section .text1, "wa"
.align 4
.section .rodata, "a"
.align 4
subidx_rmap:
.long 4 # s32
.long 33 # s32
.long 137 # s32
.type subidx_rmap,@object
.size subidx_rmap,12
.data
.section .text
.LNDBG_TXe:
# End
---------------------------------
g++ info:
address@hidden test]$ g++ -v
Reading specs from
/usr/local/gcc-3.3.3/lib/gcc-lib/i686-pc-linux-gnu/3.3.3/specs
Configured with: ../gcc-3.3.3/configure --prefix=/usr/local/gcc-3.3.3
--enable-threads=posix
--enable-languages=c,c++,f77 --enable-checking --disable-nls
Thread model: posix
gcc version 3.3.3
--
Summary: pessimise code, loose constantness
Product: gcc
Version: 3.3.3
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: smelkov at mph1 dot phys dot spbu dot ru
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14531
- [Bug c++/14531] New: pessimise code, loose constantness,
smelkov at mph1 dot phys dot spbu dot ru <=