On Sat, Jun 4, 2011 at 2:50 PM, Alexandre Oliva <aol...@redhat.com> wrote: > If cprop regards changes to debug insns as “changed”, it will perform > cfg optimizations and more, even if no non-debug insns were changed, > causing divergence between -g and -g0 compilations. > > This was observed during bootstrap-debug-lib of the SSA coalesce patch, > building a-strsea.adb with -fcompare-debug. Because of different CFGs, > cse2 chose different equivalent pseudos for an insn. -fcompare-debug > detected the difference in REG notes, even though the executable code > turned out to be the same. We can't count on this luck, though: other > optimization passes could apply different transformations to the > different CFGs, producing different executable code, which must never > happen. > > This patch fixes the problem, disregarding changes to debug insns as > “changed”. Regstrapped on x86_64-linux-gnu and i686-linux-gnu. Ok to > install?
Looks OK to me, although I can't approve it. I'm curious, though: What CFG changes or other transformations are performed without this patch? It could be a sign of a missed optimization before CPROP. Have you looked at that too? Ciao! Steven
