http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47670
Summary: Gcc 4.5.1 inconsistent optimisation of loop with mixed
32bit and 64bit arithmetic
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: argond...@gmail.com
Created attachment 23290
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23290
Output of gcc -v save-temps -O2 bug.c
int main(int argc, char *argv[])
{
int i;
long long count=0;
int ret;
for (i=0;i<9;i++)
{
count+=i*0x40000000;
}
ret=count>>32;
return ret;
}
produces different answers when compiled with
gcc -O1 bug.c (returns -1)
or
gcc -O2 bug.c (returns 9)
Judging from the assembler output with -S, this loop is optimised to a
different constant expression in the two cases.
It works with gcc 3.4.4, but not with gcc 4.5.1 (I haven't tested any other
versions yet)
(First time I've attempted to submit a bug report to an open source project, so
many apologies if this is already fixed, an issue with my understanding of C,
or in the wrong category!)
