http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46281
Summary: Inefficient unswitching (too many copies) Product: gcc Version: 4.6.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: tree-optimization AssignedTo: unassig...@gcc.gnu.org ReportedBy: davi...@gcc.gnu.org Compiling the following program with -O3: extern int gen_int(int); extern void ref_int_p(int*); void kernel3 () { int i; int j; int k; int l; int m; int a[200]; j = gen_int (0); k = gen_int (0); l = gen_int (0); m = gen_int (0); for (i = 0; i < 200; i++) { if (j < k || j < l || j < m ) // || j << 3 || k << 4) a[i] = 1; else a[i] -= j; } ref_int_p (&a[0]); return; } Gcc unswitches the loop, but generate three copies of the loop -- it should only generate 2 copies. LLVM correctly generates two copies. David