Re: [RFC] RISC-V: Add Zibi extension support

[Jiawei]

Thanks, I really appreciate it.

Please feel free to include the riscv_emit_int_compare part from my RFC.
I am also happy to help test the updated patch against current GCC trunk if
needed.


Best regards,

Jiawei

在 2026/6/4 22:06, Kito Cheng 写道:

It's OK, and your version did have more right thing in
riscv_emit_int_compare, so do you mind I include that part and add you
to coauthor in the patch in future?

Jiawei <jia...@iscas.ac.cn> 於 2026年6月4日週四 下午9:14寫道：

Thanks for the comments.

I just noticed there is already a downstream implementation in the SiFive
riscv-gcc tree:

      https://github.com/riscv/zibi/issues/2

Sorry that I missed that before sending this RFC.

Since there is already an existing implementation, I will stop pursuing this
RFC to avoid duplicating the work. Please feel free to upstream the
downstream
patch directly if you prefer. I am happy to help test it and adapt it
against
current GCC trunk if needed.


Best regards,

Jiawei

在 2026/6/4 20:47, Kito Cheng 写道:

diff --git a/gcc/config/riscv/riscv-ext.def b/gcc/config/riscv/riscv-ext.def
index b9ef0c5ea05..ef8d0400f5d 100644
--- a/gcc/config/riscv/riscv-ext.def
+++ b/gcc/config/riscv/riscv-ext.def
@@ -220,6 +220,19 @@ DEFINE_RISCV_EXT(
     /* BITMASK_BIT_POSITION*/ 7,
     /* EXTRA_EXTENSION_FLAGS */ 0)

+DEFINE_RISCV_EXT(
+  /* NAME */ zibi,
+  /* UPPERCASE_NAME */ ZIBI,
+  /* FULL_NAME */ "Branch with immediate",
+  /* DESC */ "",
+  /* URL */ ,
+  /* DEP_EXTS */ ({}),
+  /* SUPPORTED_VERSIONS */ ({{1, 0}}),

It's 0.6 on the repo?

diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index 2055e5c4a9d..38fd5d9e9ac 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -3435,6 +3435,32 @@
     [(set_attr "type" "branch")
      (set_attr "mode" "none")])

+(define_insn "*branch_zibi<mode>"

I incline this merge with *branch<mode> pattern and then split that
into eqne and others
(e.g. *branch<mode>_eqne *branch<mode>_relational_comparison)
and control the zibi by `ext` attribute

+  [(set (pc)
+       (if_then_else
+        (match_operator 1 "equality_operator"
+                        [(match_operand:X 2 "register_operand" "r")
+                         (match_operand:X 3 "zibi_cimm_operand" "zibi")])
+        (label_ref (match_operand 0 "" ""))
+        (pc)))]