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optimization/6019: doubled struct initialization
- From: Gunther Vogel <gunther dot vogel at gmx dot net>
- To: <gcc-gnats at gcc dot gnu dot org>
- Date: Wed, 20 Mar 2002 18:05:51 +0100 (CET)
- Subject: optimization/6019: doubled struct initialization
>Number: 6019
>Category: optimization
>Synopsis: doubled struct initialization
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: unassigned
>State: open
>Class: pessimizes-code
>Submitter-Id: net
>Arrival-Date: Wed Mar 20 09:16:02 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: Gunther Vogel
>Release: 3.0.4
>Organization:
>Environment:
System: Linux whiterider 2.4.17 #10 Tue Feb 26 17:24:09 CET 2002 i686 unknown
Architecture: i686
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ./configure --prefix=/usr/src/packages/BUILD/gccgpp-buildroot/usr --mandir=/share/man --with-cpu=athlon --disable-cpp --disable-nls
>Description:
The first generated movl $2538, ... instructions looks
superfluous to me. This effect occurs if and only if
optimization (gcc -O[1-3] -S t.c) is used. Using different
-march= options (i[3-6]86, athlon) moves things around a bit,
but keeps the repetition. (Please take my apology if this is
just some kind of subtle optimization I don't comprehend.)
>How-To-Repeat:
// begin file t.c
typedef struct B_ {
int b;
} B;
extern void bar(B*);
void foo()
{
B b = { 2538 };
bar(&b);
}
// end file t.c
// begin excerpt t.s generated by gcc -O2 -S t.c
foo:
pushl %ebp
movl %esp, %ebp
subl $20, %esp
movl $2538, -4(%ebp)
leal -8(%ebp), %eax
movl $2538, -8(%ebp)
pushl %eax
call bar
movl %ebp, %esp
popl %ebp
ret
// end excerpt t.s
>Fix:
unknown
>Release-Note:
>Audit-Trail:
>Unformatted: