Between gcc-4.5-20090903 (correct) and gcc-4.5-20091008 (wrong), a
bug was introduced in the expansion of _asm__() directives on AMD64.
The bug has been reproduced also in gcc-4.5-20100107 and yesterday's
first release of gcc-4.6-20100416. Here is test program, with leading
comments that reflect its test results:
/***********************************************************************
Demonstrate a bug in the handling of __asm__() in recent gcc-4.5 and
gcc-4.6 releases on AMD64:
gcc-4.1-20070723 mysqrt(4) = 2
gcc-4.1-20071126 mysqrt(4) = 2
gcc-4.1-20071231 mysqrt(4) = 2
gcc-4.1-20080211 mysqrt(4) = 2
gcc-4.1-20080218 mysqrt(4) = 2
gcc-4.1-20080407 mysqrt(4) = 2
gcc-4.1-20080630 mysqrt(4) = 2
gcc-4.2-20061031 mysqrt(4) = 2
gcc-4.2-20070124 mysqrt(4) = 2
gcc-4.2-20070207 mysqrt(4) = 2
gcc-4.2-20070815 mysqrt(4) = 2
gcc-4.2-20070905 mysqrt(4) = 2
gcc-4.2-20071128 mysqrt(4) = 2
gcc-4.2-20071219 mysqrt(4) = 2
gcc-4.2-20071226 mysqrt(4) = 2
gcc-4.2-20080102 mysqrt(4) = 2
gcc-4.2-20080213 mysqrt(4) = 2
gcc-4.2-20080220 mysqrt(4) = 2
gcc-4.2-20080409 mysqrt(4) = 2
gcc-4.2-20080806 mysqrt(4) = 2
gcc-4.2-20081015 mysqrt(4) = 2
gcc-4.2-20081126 mysqrt(4) = 2
gcc-4.2-20090121 mysqrt(4) = 2
gcc-4.2-20090325 mysqrt(4) = 2
gcc-4.3-20061118 mysqrt(4) = 2
gcc-4.3-20070209 mysqrt(4) = 2
gcc-4.3-20070511 mysqrt(4) = 2
gcc-4.3-20070720 mysqrt(4) = 2
gcc-4.3-20070914 mysqrt(4) = 2
gcc-4.3-20081016 mysqrt(4) = 2
gcc-4.3-20081127 mysqrt(4) = 2
gcc-4.3-20090122 mysqrt(4) = 2
gcc-4.3-20090524 mysqrt(4) = 2
gcc-4.3-20090816 mysqrt(4) = 2
gcc-4.3-20100103 mysqrt(4) = 2
gcc-4.4-20081017 mysqrt(4) = 2
gcc-4.4-20081128 mysqrt(4) = 2
gcc-4.4-20090123 mysqrt(4) = 2
gcc-4.4-20090526 mysqrt(4) = 2
gcc-4.4-20090818 mysqrt(4) = 2
gcc-4.4-20090908 mysqrt(4) = 2
gcc-4.4-20100105 mysqrt(4) = 2
gcc-4.4-20100112 mysqrt(4) = 2
gcc-4.5-20090528 mysqrt(4) = 2
gcc-4.5-20090820 mysqrt(4) = 2
gcc-4.5-20090903 mysqrt(4) = 2
gcc-4.5-20091008 mysqrt(4) = 0
gcc-4.5-20100107 mysqrt(4) = 0
gcc-4.6-20100416 mysqrt(4) = 0
***********************************************************************/
#include <stdio.h>
#include <stdlib.h>
double
mysqrt(double x)
{
double result;
__asm__ __volatile__("sqrtsd %0, %1" : "=x" (result) : "x" (x)); /* use
AMD64 SSE2 instruction */
return (result);
}
int
main(void)
{
double x, y;
x = 4.0;
y = mysqrt(x);
(void)printf("mysqrt(%g) = %.17g\n", x, y);
return (EXIT_SUCCESS);
}
--
Summary: Erroneous expansion of __asm__() directive
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: beebe at math dot utah dot edu
GCC build triplet: x86_64-unknown-linux-gnu
GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43782
