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c/4308: Optimisation problem (constant folding?)
- To: gcc-gnats at gcc dot gnu dot org
- Subject: c/4308: Optimisation problem (constant folding?)
- From: wilco at trimedia dot com
- Date: Wed, 12 Sep 2001 11:09:16 -0700
- Cc: wilco at trimedia dot com
>Number: 4308
>Category: c
>Synopsis: Optimisation problem (constant folding?)
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Wed Sep 12 11:15:59 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:
>Release: 3.0.1
>Organization:
>Environment:
System: Linux marilyn 2.2.18 #1 Wed Jan 24 12:28:55 GMT 2001 i686 unknown
Architecture: i686
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ./configure
>Description:
Looks like a constant folding problem with 64-bit signed shift. See
How-To-Repeat for input file.
>How-To-Repeat:
marilyn % cat tmp.i
extern int printf( const char* s, ... );
int main( )
{
long long C = 1ULL << 63, X;
int Y = 32;
X = C >> (Y & 31);
printf( "%s (%llx)\n", X != C ? "FAIL" : "OK", X );
return 0;
}
marilyn % gcc -v tmp.i
Reading specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/specs
Configured with: ./configure
Thread model: single
gcc version 3.0.1
/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/cc1 -fpreprocessed tmp.i -quiet -dumpbase tmp.i -version -o /tmp/ccrQWXBe.s
GNU CPP version 3.0.1 (cpplib) (i386 Linux/ELF)
GNU C version 3.0.1 (i686-pc-linux-gnu)
compiled by GNU C version 2.95.3 20010315 (release).
as --traditional-format -V -Qy -o /tmp/cc8zOk9j.o /tmp/ccrQWXBe.s
GNU assembler version 2.10.91 (i486-suse-linux) using BFD version 2.10.0.33
/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/collect2 -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/crtbegin.o -L/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.1 -L/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/../../.. /tmp/cc8zOk9j.o -lgcc -lc -lgcc /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/crtend.o /usr/lib/crtn.o
marilyn % a.out
OK (8000000000000000)
marilyn % gcc -O tmp.i
marilyn % a.out
FAIL (ffffffff00000000)
marilyn %
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted: