On Tue, Mar 29, 2011 at 2:44 PM, Richard Sandiford <[email protected]> wrote: > Richard Sandiford <[email protected]> writes: >> Richard Guenther <[email protected]> writes: >>> Well, I meant if the user compiles with -msse, declares such a >>> global var (which means it gets V4SFmode and not BLKmode) >>> and then uses it in a function where he explicitly disables SSE >>> then something is wrong. If he declares a BLKmode global >>> then generic vector support will happily trigger and make it work. >> >> Ah, OK. I'm just not sure whether, to take a MIPS example, >> MIPS16 functions in a "-mno-mips16" compile should behave >> differently from unannotated functions in a "-mips16" compile. >> >>> If it's just three element array-of-vector types you need why not expose >>> it via attribute((mode(xyz))) only? You could alias that mode to BLKmode >>> if neon is not enabled ... >> >> I don't think that really changes anything. Getting the non-BLK mode >> on the array type seems like the easy part. The difficult part is >> dealing with the fallout when the array is defined in a Neon context >> and used in a non-Neon context. > > As a follow-up to this, I think the current definition of TYPE_MODE > is too restrictive even for the vector case. Single-element structures > get the modes of their fields, and similarly for arrays. So if we modify > the original 38240 testcase a bit, we still get a difference: > > ------------------------------------------------------------------------- > #if STRUCT > typedef struct { > float x __attribute__ ((__vector_size__ (16), __may_alias__)); > } V; > #else > typedef float V __attribute__ ((__vector_size__ (16), __may_alias__)); > #endif > > V __attribute__((target("sse"))) f(const V *ptr) { return *ptr; } > ------------------------------------------------------------------------- > > Without -DSTRUCT, this generates the same code regardless of whether > you compile with -msse. But with -DSTRUCT, you get: > > movaps (%rdi), %xmm0 > ret > > with -msse and: > > movq (%rdi), %rax > movq %rax, -24(%rsp) > movq 8(%rdi), %rax > movq %rax, -16(%rsp) > movdqa -24(%rsp), %xmm0 > ret > > with -mno-sse. > > I think your argument is that most/all uses of TYPE_MODE are a mistake. > But I still think it makes sense to say that types have a natural mode > _in a given context_, just not globally. So how about replacing it with > a current_mode_of_type function? That makes it obvious that TYPE_MODE is > not a global property, and that it isn't really a simple accessor any more. > We could then make it recompute the mode for all types, possibly with a > cache if that's necessary for performance reasons.
Well, ok. That current_mode_of_type wouldn't make sense when for example expanding global initializers (neither would looking at TYPE_MODE). But - what's the natural mode to choose for global entities? After all we have to stick something into TYPE_MODE and DECL_MODE. But yes, changing the TYPE_MODE users over to current_mode_of_type (or rather mode_of_type_in_fn (struct function *, tree)) would be nice (and then get rid of the TYPE_MODE hack). Richard. > Richard >
