Slightly different and less arcane. Tested on x86_64-unknown-linux-gnu, applied to trunk and branch.
Richard. 2013-04-03 Richard Biener <rguent...@suse.de> PR tree-optimization/55964 * gcc.dg/torture/pr55964-2.c: New testcase. Index: gcc/testsuite/gcc.dg/torture/pr55964-2.c =================================================================== --- gcc/testsuite/gcc.dg/torture/pr55964-2.c (revision 0) +++ gcc/testsuite/gcc.dg/torture/pr55964-2.c (working copy) @@ -0,0 +1,21 @@ +/* { dg-do compile } */ +/* { dg-options "-ftree-loop-distribution -funswitch-loops" } */ + +struct test_struct { + int a, b[10], c[10], d[10]; +}; + +extern struct test_struct* new_struct; + +void testfunc(struct test_struct* old_struct) +{ + int i; + for (i = 0; i < 10; ++i) + { + new_struct->b[i] = old_struct ? old_struct->b[i] : -1; + new_struct->c[i] = old_struct ? old_struct->c[i] : 0; + new_struct->d[i] = old_struct ? old_struct->d[i] : 0; + } + if (old_struct) + old_struct->a++; +}