Microsoft KB Archive/149964

= FIX: C1001 on Large Basic Block with Optimizations Enabled =

Article ID: 149964

Article Last Modified on 7/5/2005

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APPLIES TO


 * Microsoft Visual C++ 4.0 Professional Edition
 * Microsoft Visual C++ 5.0 Learning Edition

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This article was previously published under Q149964



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)

NOTE: Basic blocks are straight line sections of generated code for which there is no flow of control into or out of the section.



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 */
 * 1) include "windows.h"

long mm(long, long, long, long); long ff(long, long); long dd(long, long, long); long ee(long, long, long); long aa(long *,long,long,long,long,long,long,long,long); typedef struct {int ii5; int nn6; int nn7; int ii6;} nn4; typedef struct {int ll2; int ii8; int ii9;} nn5; typedef struct {char ii7[1]; long x2; nn4 a2; short bb; short gg;} **ss;


 * 1) 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; } }

Additional query words: 4.00 10.00

Keywords: kbbug kbfix kbcompiler KB149964

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