> Message du 20/10/21 17:14
> De : "Vladislav Yaglamunov"
> A : [email protected]
> Copie à :
> Objet : [Valgrind-users] Cubic root of zero gives wrong result with clang
> 64-bit
>
>Hi,
>I am using Valgrind 3.17.0 and noticed a strange behavior while running a code
>compiled with clang:
>
> #include
>
> int main() {
> long double x = std::cbrtl(0.0L);
> printf("%Lf", x);
>
> return 0;
> }
I just did a test with g++. I had to modify the code a bit to prevent the
compiler replacing the cbrtl() call with just a zero:
#include
#include
int main() {
volatile long double arg{0.0L};
long double x = std::cbrtl(arg);
printf("%Lf", x);
return 0;
}
This seems to work OK, both default and -m32.
The asm for that is
00000000004011a5 :
4011a5: 55 push %rbp
4011a6: 48 89 e5 mov %rsp,%rbp
4011a9: 48 83 ec 20 sub $0x20,%rsp
4011ad: d9 ee fldz
4011af: db 7d e0 fstpt -0x20(%rbp)
4011b2: db 6d e0 fldt -0x20(%rbp)
4011b5: 48 8d 64 24 f0 lea -0x10(%rsp),%rsp
4011ba: db 3c 24 fstpt (%rsp)
4011bd: e8 8e fe ff ff callq 401050
4011c2: 48 83 c4 10 add $0x10,%rsp
4011c6: db 7d f0 fstpt -0x10(%rbp)
4011c9: ff 75 f8 pushq -0x8(%rbp)
4011cc: ff 75 f0 pushq -0x10(%rbp)
4011cf: bf 04 20 40 00 mov $0x402004,%edi
4011d4: b8 00 00 00 00 mov $0x0,%eax
4011d9: e8 62 fe ff ff callq 401040
4011de: 48 83 c4 10 add $0x10,%rsp
4011e2: b8 00 00 00 00 mov $0x0,%eax
4011e7: c9 leaveq
4011e8: c3 retq
I'll have a go with clang++ at home tonight.
A+
Paul
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