------- Comment #3 from aoliva at gcc dot gnu dot org 2009-11-18 16:30 ------- Different UIDs affect hash table walks, which in turn may affect codegen. We've had several -g/-g0 codegen differences ultimately caused by decl UID differences, and they were detected and fixed long before -fcompare-debug was even introduced, i.e., they were detected with the compare-debug script that compares actual generated code.
That's why -fcompare-debug must report such differences. Even if the code ends up the same in one particular testcase, supersets of that testcase would likely diverge. Disregarding the UIDs in -fcompare-debug would hide errors. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42088
