https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90867
Bug ID: 90867
Summary: Multiplication or typecast of integer and double
always zero when...
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: sven.schm...@gmx-topmail.de
Target Milestone: ---
Created attachment 46485
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46485&action=edit
Compiler output text
A multiplication of integer with double or a typecast of integer to double is
always zero when compiling with -march=native and the function is defined
"GENERIC" with "__attribute__ ((target ("arch=x86-64")))" or any other arch.
The bug occurs an all gcc 64-bit (x86-64) for Linux since gcc-6 I've tested.
Not affected is gcc 32-bit (i386) or other systems like gcc for mingw.
-----
#include <stdint.h>
#include <stdio.h>
/*
* no opcode optimization allowed
*/
#if __i386__
# define GENERIC __attribute__ ((target ("arch=i386")))
#else
# define GENERIC __attribute__ ((target ("arch=x86-64")))
#endif
uint64_t freq = 3600000000UL; /* 3.6 GHz = 3600.0 MHz */
GENERIC int main (void)
{
printf("freq = %f Hz\n", (double)freq);
printf("freq = %f kHz\n", 1e-3 * freq);
printf("freq = %f MHz\n", 1e-6 * freq);
printf("freq = %f GHz\n", 1e-9 * freq);
return 0;
}
-----
Compile with: gcc -v -save-temps -Wall -Wextra -march=native test.c -o test
Result when running is:
-----
freq = 0.000000 Hz
freq = 0.000000 kHz
freq = 0.000000 MHz
freq = 0.000000 GHz
-----
Compiling same code with -m32...
gcc -m32 -v -save-temps -Wall -Wextra -march=native test.c -o test
...gives expected results:
-----
freq = 3600000000.000000 Hz
freq = 3600000.000000 kHz
freq = 3600.000000 MHz
freq = 3.600000 GHz
-----
gcc --version: gcc (Debian 8.3.0-6) 8.3.0
gcc compiles assembler code for the old FPU and there is a bug in machine code.
When compiling same code without architecture restrictions assembler code is
build for SSE unit without bug.
Compiler output file is appended.
Best regards
Sven
