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[Bug target/16562] [ H8300 Target] Wrong code with -O2, -O3 optimizations
- From: "anilp1 at kpitcummins dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 4 Aug 2004 05:20:28 -0000
- Subject: [Bug target/16562] [ H8300 Target] Wrong code with -O2, -O3 optimizations
- References: <20040715094601.16562.asgarij@kpitcummins.com>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Additional Comments From anilp1 at kpitcummins dot com 2004-08-04 05:20 -------
Hi,
The workaround to avoid bug is to pass either of following option along
with -O2 ,
-fno-loop-optimize
-fno-strength-reduce
This bug is not target dependent as was first impression.
Since counting variable is of type unsigned long, the number of instructions
in loop for plain H8/300 are 7. So problem doesn't crop up for plain H8/300.
If we change data type of counting variable to unsigned int (16 bits) and
value also within range of 16 bits ( less than 65535) then bug can be seen in
case of plain H8/300.
Bug is not observed in following program code,
//test.c
void theLoop( void )
{
unsigned long int cnt;
cnt = 0L;
do{
cnt++;
asm("nop");
} while (cnt < 1000000L);
}
//test.c
Compiled with -S -O2 -ms options.
The number of instructions in loop becomes 4 in above case. Hence bug is not
observed.
I tracked the problem to loop.c, line no. 5358 (gcc 3.5 snapshot dated 25 July
2004).
Following call doesn't take place for insn_count more than 4
since "unrolled_insn_copies <= insn_count" this condition is dissatisfied.
unroll_loop (loop, insn_count, 1);
In case of H8S target and insn_count 3, call takes place and the magic number
50 appears instead of 1.
This magic number is also dependent on number of iterations of loop.
Will it be ok to add additional condition as insn_count > 4 while calling
unroll_loop at line 5358 ?
Please comment.
Regards,
Anil Paranjpe
KPIT Cummins InfoSystems Ltd.
Pune, India
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16562