[Bug c/77365] New: Wrong result with -fcaller-saves on i386

["olebole at debian dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77365

            Bug ID: 77365
           Summary: Wrong result with -fcaller-saves on i386
           Product: gcc
           Version: 6.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: olebole at debian dot org
  Target Milestone: ---

With gcc-6.2.0 on Debian, I get a wrong result with the following code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

double f(double x) {
  return sqrt(1.0 - x) - 1.0;
}

double g(double x) {
  double res = f(x);
  printf("res=%.20g\n", res);
  return res;
}

int main(void) {
  double x = 3.1740879016271733482e-09;
  double r1 = f(x);
  double r2 = g(x);
  printf("r1=%.20g r2=%.20g diff=%20g\n", r1, r2, r2-r1);
  exit(0);
}  

Compile this with `gcc -O -o m m.c -lm` gives

r =-1.5870439520936432953e-09
r1=-1.5870439407095204842e-09 r2=-1.5870439520936432953e-09 diff=       
-1.13841e-17

Adding `-fno-caller-saves` gives the expected result.