> Hi, > Sorry for late response, I was travelling. > I tried to verify the alignments are monotonously worse with the > attached patch (verify.diff), > which asserts that alignment lattice is not better than bits lattice > during each propagation > step in propagate_constants_accross_call(). > Does that look OK ?
Yes, that looks fine to me. > > ipa-cp-alignment has better alignments than ipa-bit-cp in following cases: > > a) ipa_get_type() returns NULL: ipa-bits-cp sets lattice to bottom if > ipa_get_type (param) returns NULL, > for instance in case of K&R function, while ipa-cp-alignment doesn't > look at param types, > and can propagate alignments. > The following assert: > if (bits_lattice.bottom_p ()) > gcc_assert (align_lattice.bottom_p()) > > triggered for 400.perlbench, 403.gcc, 456.hmmer and 481.wrf due to > ipa_get_type() > returning NULL. I am not really sure how to handle this case, since we > need to know parameter's > type during bits propagation for obtaining precision. Indeed, it looks like a but in alignment propagation? > > b) This happens for attached test-case (test.i), > which is a reduced (and slightly modified) test-case from 458.sjeng. > Bits propagation sets lattice to bottom, while alignment propagation > propagates <align 1, misalign 0>. > > In bits_lattice::meet_with_1 > m_mask = other_mask = 0x0fffffffffffffff0 > m_value = 0x7 > other_value = 0x8 > > In this case meet operation sets m_mask to: > (m_mask | mask) | (m_value ^ other_value) = 0x0fffffffffffffff0 | > (0xf) == 0x0ffffffffffffffff > and hence the bits lattice is set to bottom. > I suppose it doesn't matter for this case if bits propagation sets > lattice to bottom, > since propagating <align 1, misalign 0> isn't really useful ? Hmm, Martin probably knows how the alignment is defined here. If it is power of two, then it would be alignment to even byte :) > > The attached patch (alignprop-4.diff) removes ipa-cp-alignment, and > checks for misalign against old_misalgin and prints message in the dump file > if they mismatch. Testing in progress. Looks OK to me (with Changelog please) > diff --git a/gcc/common.opt b/gcc/common.opt > index 0e01577..601a347 100644 > --- a/gcc/common.opt > +++ b/gcc/common.opt > @@ -1565,10 +1565,6 @@ fipa-cp-clone > Common Report Var(flag_ipa_cp_clone) Optimization > Perform cloning to make Interprocedural constant propagation stronger. > > -fipa-cp-alignment > -Common Report Var(flag_ipa_cp_alignment) Optimization > -Perform alignment discovery and propagation to make Interprocedural constant > propagation stronger. I wonder if we should mark option as obsoleted and point users to consider -fno-ipa-bit-cp instead. Honza
