http://d.puremagic.com/issues/show_bug.cgi?id=9387



--- Comment #9 from Don <clugdbug@yahoo.com.au> 2013-01-28 01:03:34 PST ---
...and I can reproduce your bug.

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--- Comment #10 from Don <clugdbug@yahoo.com.au> 2013-01-28 01:13:35 PST ---
I think there is an uninitialized variable in there. When I compile with -O, if I run the same executable multiple times, sometimes it passes, sometimes it fails.

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--- Comment #11 from Stephan <stephan.schiffels@mac.com> 2013-01-28 06:57:56 PST ---
Hi Don,

glad to hear that you can reproduce the bug! I tested initializing all
variables by hand, and the bug still occurs.
Thanks for the suggestion to use std.numeric. Looks very useful! The Numerical
Recipes Code style is worse than horrible! All those 1-letter variables...

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code


--- Comment #12 from Don <clugdbug@yahoo.com.au> 2013-01-29 15:13:51 PST ---
Here is a more reduced test case (still enormous):
Without -O, it returns on the first pass through the loop. With -O, one of two
things happen:
(a) it hits the assert(0) on the first pass through the loop; or
(b) it generates an alignment hardware exception.

It looks as though it is a issue with misalignment of SSE registers. Removing the assert(0) causes an ICE.

---
import std.math : abs;

void minimize()
{
    double a,b,d=0.0,etemp,fu,fv,fw,fx;
    double p;
    double q,r,tol1,tol2,u,v,w,x,xm;
    double e=0.0;
    double ax,bx,cx,fa,fb,fc;
    double tol;
  ax = 2.8541;
  bx = 3;
  cx = 3.0458;
  fa = 0.145898;
  fb = 0;
  fc = 0.381966;
 tol = 3.0e-8;

    a= ax;
    b= cx;
    v = bx;
    w = bx;
    x = bx;
    fx = 0;
    fv = fx;
    fw = fx;

  a = 2.97871347812973974456; b = 3.0458; v =2.9442711606; w =2.9787134781;
  x = 3;  fx= 0; fv = 0.00310570354087098691;
  fw = 0.00045311601333306815;
  e =-0.0557288394;
  d = -0.0212865219;
    for (int iter=0;iter<1;iter++) {
      xm=0.5*(a+b);
      tol1=tol*abs(x);
      tol2=2.0*(tol1);
      if (abs(x-xm) <= (tol2-0.5*(b-a))) {
        return;
      }
      if (abs(e) > tol1) {
       r=(x-w)*(fx-fv);
        q=(x-v)*(fx-fw);
        p=(x-v)*q-(x-w)*r;
        q=2.0*(q-r);
        if (q > 0.0) p = -p;
        q=abs(q);
        etemp=e;
        e=d;
        if (abs(p) >= abs(0.5*q*etemp) || q < p) {
          d= b-x;
        }
        else {
          d=p/q;
          u=x+d;
          if (u-a < tol2 || b-u < tol2)
            d = xm - x;
        }
      }
      else { d= (e=(x >= xm ? a-x : b-x)); }
      u= (abs(d) >= tol1) ? x+d : x+3.0e-8;

     if (u < 3.01) return;
     else
        assert(0);  // FAILS HERE

      fu = (u-3.0)*(u-3.0);

      if (fu <= fx) {
        assert(0);
      }
    }
}

void main() {
  minimize();
}

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice
         OS/Version|Mac OS X                    |All


--- Comment #13 from Don <clugdbug@yahoo.com.au> 2013-01-29 23:51:04 PST ---
A reduced test case for the ICE:

import std.math : abs;

void bug9387()
{
    double x = 3;
    double r = (x-2.1)*0.1;
    double q = (x-2.1)*0.1 - r;
    double p = (x-2.1)*q - (x-2.1)*r;

    if (q > 0.0) p = -p;
    if (abs(p) >= q ) { }
}
---
dmd -O -m64 bug.d
Internal error: backend/cgcod.c 769

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--- Comment #14 from Don <clugdbug@yahoo.com.au> 2013-01-30 00:20:15 PST ---
ICE, further reduced:
--------------
void bug9387a(double x) { }

void ice9387()
{
    double x = 0.3;
    double r = x*0.1;
    double q = x*0.1 + r;
    double p = x*0.1 + r*0.2;
    if ( q )
        p = -p;
    bug9387a(p);
}

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--- Comment #15 from Don <clugdbug@yahoo.com.au> 2013-01-30 03:58:21 PST ---
And a reduction for the wrong-code case. This sometimes segfaults but usually hangs. Looks like the saved RBX register gets trampled:

double brent(double x) { return x; }

void wrong9387()
{
    for (int iter=0; iter<1; iter++) {
        double v =2.94;
        if (brent(v)<= 2.9) { return; }
        double w = 2.97;
        double r = (0.2-w) * 0.1;
        double q = (0.2-v) * 0.1 - r;
        double p = 0.7*q - (0.2-v)*0.3;
        if (q > 0.0) p = -p;
        q = brent(q);
        double d = p-q;
        if (2.94 + d)
            w = v -v;
        brent(w);
    }
}

void main()
{
  wrong9387();
}

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--- Comment #16 from github-bugzilla@puremagic.com 2013-01-30 14:40:23 PST ---
Commit pushed to dmd-1.x at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/bfa5d0f0ba80c7ff6e0d67806714763584666fb2 fix Issue 9387 - Compiler switch -O changes behavior of correct code

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--- Comment #17 from Walter Bright <bugzilla@digitalmars.com> 2013-01-30 14:42:56 PST ---
https://github.com/D-Programming-Language/dmd/pull/1584

Thanks, Don, for the minimizations which made it easy for me to find the problem. It was not a regression, although it looked like one. The bug is nasty and I'm glad to get it fixed.

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--- Comment #18 from Stephan <stephan.schiffels@mac.com> 2013-01-30 15:29:45 PST ---
Don and Walter, thanks for reducing the code and fixing the bug, all on a very short timescale! This is going to be a very important fix for me. Using the optimization switch is critical for me.

Stephan

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