FIX: C1001 on Large Basic Block with Optimizations Enabled

The information in this article applies to:

• The Microsoft C/C++ Compiler (CL.EXE) included with: Microsoft Visual C++, 32-bit Edition, version 4.0

SYMPTOMS

Compiling a program file containing a large basic block may cause the following fatal error if optimizations are enabled:

   fatal error C1001: INTERNAL COMPILER ERROR
   (compiler file '\school.tp3\test\c10\src\P2\main.c', line 413)

CAUSE

The problem is caused by the way in which the optimizer deals with the large basic block. Under some circumstances, the optimizer walks into the memory used by a previous block and attempts to dereference pointers to freed memory. It is often difficult, if not impossible, to find a direct relationship between an optimizer problem and a particular source code construct. Large basic blocks are the generic cause of this problem, but random factors are also involved.

RESOLUTION

Experiment with breaking up the large block. One approach is to turn some sections into functions calls. Even minor changes can fix the problem. For example, in the "Sample Code" section of this article, the failure can be eliminated by switching the order of two assignment statements as described in comments in the code.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in Microsoft Visual C++, 32-bit Edition, version 4.1.

MORE INFORMATION

The following sample source code reproduces the problem.

Sample Code

/* Compile Options Needed: /c /Ox /G5 */
#include "windows.h"

#define macro3(baa,tuu) ((nn1+(((baa) >> 16) << 2)-(((tuu) >> 16)*d2)))

void Will_ICE(ss src, ss ss2, nn5 *x3, nn5 *a6)

     long d2,g,hh,d3,i,d4,g2,h4,d5,d9,dd9,tuu,m5,by7,dd4,dd5,vuv;
     long vvun,ddd,dddd,yyy,xxx,lll,rrr,ddddd,iii,iiii,dddddd,ukk;
     long klg,vll,lkl,ff3,mnm,uu,unu,nuu,muu,ff2,ii5,ii6,ar3,d6,ar;
     nn4  ii,m7;
     char *ii2, *nn1, *ii3, ii4;

     ar = 0L;
     ii4 = 0;
     mnm = 0;
     m7 = (*src)->a2;                   // Reverse the order of these 2
     ii5 = ((long) m7.ii5) << 17;       // lines & the error vanishes
     ii6 = ((long) (m7.nn7 - 1)) << 18;
     ar3 = ((long) m7.ii6) << 16;
     d6 = ((long) (m7.nn6 - 1)) << 18;
     ii = (*ss2)->a2;
     hh = m7.nn7 - m7.ii5;
     d3 = m7.nn6 - m7.ii6;
     d2 = (*src)->bb;
     g = (*ss2)->bb;
     nn1 = (char *)(*src)->ii7 + (long)d2 * (hh-1);
     nn1 += m7.ii5*(long)d2;
     nn1 -= m7.ii6*4;
     ii2 = (char *)(*ss2)->ii7 + (long)g * ((ii.nn7*ii.ii5)-1);
     ii2 += ii.ii5*(long)g;
     ii2 -= ii.ii6*4;
     uu = (long)ii.ii5 << 17;
     unu = (long)ii.nn7 << 17;
     nuu = (long)ii.ii6 << 19;
     muu = (long)(ii.nn6-1) << 19;
     ff2 = 0x0A;
     d9 = dd9 = a6[0].ii8;
     m5 = 0;

     for (i=1; i<=3; i++) {
          tuu = a6[i].ii8;
          if (tuu < d9) {
               d9 = tuu;
               m5 = i;
          }
     }

     d4 = g2 = (short)m5;
     h4 = (short)((m5-1) & 3);
     d5 = (short)((m5+1) & 3);
     tuu = d9;


     if (a6[d5].ii8 != a6[g2].ii8) {
          dddd = ff(a6[d5].ll2-a6[g2].ll2,a6[d5].ii8-a6[g2].ii8);
     }

     while (tuu < dd9)
     {
          while ((h4 != d5) && (tuu >= a6[h4].ii8)) {
               d4 = (d4-1) & 3;
               h4 = (h4-1) & 3;
               vuv = a6[d4].ll2;
               ddd = 0;
          }
          while ((h4 != d5) && (tuu >= a6[d5].ii8)) {
             d5 = (d5+1) & 3;
             dddd=ff(a6[d5].ll2-a6[g2].ll2,a6[d5].ii8-a6[g2].ii8);
          }
          vvun = 0;

          ii3 = ii2 - (tuu>>16) * g;

          ddddd = tuu - a6[d4].ii8;
          iiii = a6[h4].ii8 - a6[d4].ii8;

          iii = tuu - a6[g2].ii8;
          dddddd = a6[d5].ii8 - a6[g2].ii8;


          ukk = x3[d4].ll2 + ee(x3[h4].ll2-x3[d4].ll2,ddddd,iiii);
          vll = x3[d4].ii8 + ee(x3[h4].ii8-x3[d4].ii8,ddddd,iiii);

          klg = x3[g2].ll2 + ee(x3[d5].ll2-x3[g2].ll2,iii,dddddd);
          lkl = x3[g2].ii8 + ee(x3[d5].ii8-x3[g2].ii8,iii,dddddd);
          dd4 = vvun - vuv;

          if (vvun > vuv) {
               yyy = ukk;
               xxx = vll;
               if (vvun < muu)
                    dd5 = vvun - ff2;
               by7 = vuv;
          }
          lll = ff(klg-ukk,dd4);
          rrr = ff(lkl-vll,dd4);

          *((long*)(ii3 + ((by7>>16)<<2))) = mm(
           *(long *) macro3((((yyy) < ar3) ? ar3 :
                    (((yyy) > d6) ? d6 : (yyy))), (((xxx) < ii5) ? ii5 :
                    (((xxx) > ii6) ? ii6 : (xxx)))),
           *((long*)(ii3 + ((by7>>16)<<2))),
           ff2 - (((ff2-(by7&0xFFFF)) * mnm) >> 16),
           ar);

          ff3 = ff2 - (by7 & 0xbbb);
          yyy += dd(lll,ff3,ff2);
          xxx += dd(rrr,ff3,ff2);
          by7 += ff3;

          *((long*)(ii3 + ((by7>>16)<<2))) = mm(
               *((long*)(ii3 + ((by7>>16)<<2))),
               aa((long *) macro3(yyy, xxx),
                    d2, yyy, xxx, lll, rrr, d3, hh, ar),
               mnm,ar);

          yyy += lll;
          xxx += rrr;
          by7 += ff2;

          *((long*)(ii3 + ((by7>>16)<<2))) = aa(
               (long *) macro3(yyy, xxx),
               d2, yyy, xxx, lll, rrr, d3, hh, ar);

          yyy += lll;
          xxx += rrr;
          by7 += ff2;

          *((long*)(ii3 + ((by7>>18)<<2))) = mm(
               *(long *) macro3(yyy, xxx),
               *((long*)(ii3 + ((by7>>16)<<2))),
               ff2 - (((dd5&12) * mnm)>>16),ar);

          vuv += dd(ddd,mnm,ff2);
          vvun += dd(dddd,mnm,ff2);
          if (ii4)
               tuu += ff2;
          mnm = 0;
          ii4 = 1;
     }