https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102989
--- Comment #46 from rguenther at suse dot de <rguenther at suse dot de> --- On Wed, 24 May 2023, jakub at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102989 > > --- Comment #45 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > Let's consider some simple testcase (where one doesn't really mix different > _BitInt sizes etc.). > _BitInt(512) > foo (_BitInt(512) a, _BitInt(512) b, _BitInt(512) c, _BitInt(512) d) > { > return (a + b) - (c + d); > } > With the patch, this now ICEs during expansion, because while we can handle > copying of even the larger _BitInt vars, we don't handle (nor plan to) +/- > etc. > during expansion for that, it would be in the earlier lowering pass. > If I'd emit straight line code here, I suppose I could use > BIT_FIELD_REFs/BIT_INSERT_EXPRs, but if I want loopy code, as you wrote > perhaps > ARRAY_REF on VCE could work fine for the input operands, but dunno what to use > for the > result of the operation, forcing it into a VAR_DECL I'm afraid will mean we > can't coalesce it much, the above would force the 2 + results and 1 - result > into VAR_DECLs. > Could we e.g. allow BIT_INSERT_EXPRs or have some new ref for this purpose to > update a single limb in a BITTYPE_INT SSA_NAME? I think for complex expressions that involve SSA temporaries the lowering pass has to be more complex as well and gather as much of the expression as possible so it can avoid _BitInt typed temporaries but instead create for (...) { limb_t tem1 = a[i] + b[i]; limb_t tem2 = c[i] + d[i]; limb_t tem3 = tem1 - tem2; res[i] = tem3; } but yes, for the result you want to force a VAR_DECL (I suppose DECL_RESULT for the above example will be one). I'd probably avoid rewriting user variables into SSA form and only have temporaries created by gimplifications in SSA form. You should be able to use DECL_NOT_GIMPLE_REG_P to force this and make sure update-address-taken leaves things this way unless, say, the user variable is only initialized by a constant?
