[PATCH] RISC-V: avoid splitting small constant in i_extrabit pattern

[Lin Sinan via Gcc-patches]

From: Sinan Lin <linsinan....@linux.alibaba.com>

there is no need to split an xori/ori with an small constant. take the test
case `int foo(int idx) { return idx|3; }` as an example,

rv64im_zba generates:
        ori     a0,a0,3
        ret
but, rv64im_zba_zbs generates:
        ori     a0,a0,1
        ori     a0,a0,2
        ret

with this change, insn `ori r2,r1,3` will not be splitted in zbs.
---
 gcc/config/riscv/predicates.md                     |  2 +-
 .../gcc.target/riscv/zbs-extra-bit-or-twobits.c    | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/zbs-extra-bit-or-twobits.c

diff --git a/gcc/config/riscv/predicates.md b/gcc/config/riscv/predicates.md
index 0d9d7701c7e..8654dbc5943 100644
--- a/gcc/config/riscv/predicates.md
+++ b/gcc/config/riscv/predicates.md
@@ -399,7 +399,7 @@
 (define_predicate "uimm_extra_bit_or_twobits"
   (and (match_code "const_int")
        (ior (match_operand 0 "uimm_extra_bit_operand")
-           (match_operand 0 "const_twobits_operand"))))
+           (match_operand 0 "const_twobits_not_arith_operand"))))
 
 ;; A CONST_INT operand that fits into the negative half of a
 ;; signed-immediate after a single cleared top bit has been
diff --git a/gcc/testsuite/gcc.target/riscv/zbs-extra-bit-or-twobits.c 
b/gcc/testsuite/gcc.target/riscv/zbs-extra-bit-or-twobits.c
new file mode 100644
index 00000000000..ef7ed60461a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zbs-extra-bit-or-twobits.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zbs -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" } } */
+
+int or_two_bit(int idx) {
+    return idx|3;
+}
+
+int xor_two_bit(int idx) {
+    return idx^3;
+}
+
+/* { dg-final { scan-assembler-times "\tori\t" 1 } } */
+/* { dg-final { scan-assembler-times "\txori\t" 1 } } */
-- 
2.19.1.6.gb485710b