If-conversion is turning '(a >= 0) ? b : 0' into a branchless sequence
not a5,a0
srai a5,a5,63
and a0,a1,a5
missing the opportunity to combine the NOT and AND into an ANDN.
This adds a define_split to help the combiner reassociate the NOT with
the AND.
gcc/ChangeLog:
* config/riscv/bitmanip.md: New define_split.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/zbb-srai-andn.c: New test.
---
gcc/config/riscv/bitmanip.md | 13 +++++++++++++
gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c | 15 +++++++++++++++
2 files changed, 28 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c
diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index b44fb9517e7..d26f3567182 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -128,6 +128,19 @@
[(set_attr "type" "bitmanip")
(set_attr "mode" "<X:MODE>")])
+;; '(a >= 0) ? b : 0' is emitted branchless (from if-conversion). Without a
+;; bit of extra help for combine (i.e., the below split), we end up emitting
+;; not/srai/and instead of combining the not into an andn.
+(define_split
+ [(set (match_operand:DI 0 "register_operand")
+ (and:DI (neg:DI (ge:DI (match_operand:DI 1 "register_operand")
+ (const_int 0)))
+ (match_operand:DI 2 "register_operand")))
+ (clobber (match_operand:DI 3 "register_operand"))]
+ "TARGET_ZBB"
+ [(set (match_dup 3) (ashiftrt:DI (match_dup 1) (const_int 63)))
+ (set (match_dup 0) (and:DI (not:DI (match_dup 3)) (match_dup 2)))])
+
(define_insn "*xor_not<mode>"
[(set (match_operand:X 0 "register_operand" "=r")
(not:X (xor:X (match_operand:X 1 "register_operand" "r")
diff --git a/gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c
b/gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c
new file mode 100644
index 00000000000..afe9fba5f05
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zbb-srai-andn.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zbb -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-Os" "-Oz" } } */
+
+long long foo0(long long a, long long b)
+{
+ if (a >= 0)
+ return b;
+
+ return 0;
+}
+
+/* { dg-final { scan-assembler-times "srai\t" 1 } } */
+/* { dg-final { scan-assembler-times "andn\t" 1 } } */
+
--
2.34.1
