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From: "vineetg at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/110748] RISC-V: optimize store of DF 0.0
Date: Thu, 20 Jul 2023 17:24:39 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110748

--- Comment #8 from Vineet Gupta <vineetg at gcc dot gnu.org> ---
(In reply to Jeffrey A. Law from comment #5)
> I'd bet it's const_0_operand not allowing CONST_DOUBLE.

Correct.

> The question is what unintended side effects we'd have if we allowed
> CONST_DOUBLE 0.0 in const_0_operand.

Exactly. I had the same concern.=20
I do have a hack which creates a new predicate and that seems to do the tri=
ck.

+(define_predicate "const_0hf_operand"
+  (and (match_code "const_double")
+       (match_test "op =3D=3D CONST0_RTX (GET_MODE (op))")))
+
+(define_predicate "reg_or_0_operand_inc_hf"
+  (ior (match_operand 0 "reg_or_0_operand")
+       (match_operand 0 "const_0hf_operand")))

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc

-  if (!register_operand (dest, mode) && !reg_or_0_operand (src, mode))
+  if (!register_operand (dest, mode) && !reg_or_0_operand_inc_hf (src, mod=
e))
     {

And it seems to be generating the desired int 0 for double 0.0.

However to Kito's point, this indeed works in gcc 12 so I first need to bis=
ect
what regressed it in 13.=