On 09/10/2026 16:22, Richard Sandiford wrote:
Andrew Stubbs <[email protected]> writes:
On 09/10/2026 12:15, Richard Sandiford wrote:
Sorry, a couple of other things:
+
+ rtx new_addr
+ = (REG_P (addr)
+ ? simplify_gen_subreg (addr_elt_mode, addr, addrmode,
+ addr_byte)
+ : simplify_subreg (addr_elt_mode, addr, addrmode, addr_byte));
I think we should use simplify_gen_subreg unconditionally unless there's
a specific reason not to. This is a simplification regardless of what
the address is.
I tried this and got an ICE. AFAICT, simplify_gen_subreg does the wrong
thing (in this situation) when the address has an offset:
(mem/i:V8QI (plus:V8DI (reg:V8DI 720)
(vec_duplicate:V8DI (const_int 0))))
It tries to wrap the plus in a subreg, which is not valid. So, I'm going
to leave this bit as-is, unless you have a better suggestion?
Why's it not valid though?
gcn_addr_space_legitimate_address_p rejects it because there's no
instruction that can do that in a load/store instruction.
Is that not how that's supposed to work?
There's also a chance to fix it in gcn_addr_space_legitimize_address, so
I'm trying to figure out if that's something it should be doing.
The testcase is trying to convert
(mem/i:V8QI (plus:V8DI (reg:V8DI 720)
(vec_duplicate:V8DI (const_int 0))))
into
(mem:QI (subreg:DI (plus:V8DI (reg:V8DI 720)
(vec_duplicate:V8DI (const_int 0)))
0))
Which is because CSE is trying to split this
(set (mem/i:V8QI (plus:V8DI (reg:V8DI 720)
(vec_duplicate:V8DI (const_int 0))))
(const_vector:V8QI [(const_int 0 [0]) repeated x8]))
into 8 separate operations. The comment says "These are templates and
don't actually get emitted but are used to tell CSE how to get to a
particular constant."
Anyway, if I change gcn_addr_space_legitimate_address_p to allow the
subreg pattern the CSE pass works and eventually decides to do nothing.
I'm trying to work out if there are other consequences to allowing that.
Maybe I should allow it only when "strict == false"?
Thoughts?
Andrew
