Users might use explicit arithmetic operations to create a mask and
then and it, in a sequence like
cond = (bits >> SHIFT) & 1;
mask = ~(cond - 1);
val &= mask;
which will present as a single-bit sign-extract.
Dependening on what combination of XVentanaCondOps and Zbs are
available, this will map to the following sequences:
- bexti + czero, if both Zbs and XVentanaCondOps are present
- andi + czero, if only XVentanaCondOps is available and the
sign-extract is operating on bits 10:0 (bit 11
can't be reached, as the immediate is
sign-extended)
- slli + srli + and, otherwise.
gcc/ChangeLog:
* config/riscv/zicond.md: Recognize SIGN_EXTRACT of a
single-bit followed by AND for Zicond.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/zicond-le-01.c: New test.
Signed-off-by: Philipp Tomsich <philipp.toms...@vrull.eu>
---
gcc/config/riscv/zicond.md | 45 +++++++++++++++++++
gcc/testsuite/gcc.target/riscv/zicond-le-01.c | 16 +++++++
2 files changed, 61 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/riscv/zicond-le-01.c
diff --git a/gcc/config/riscv/zicond.md b/gcc/config/riscv/zicond.md
index 9d1ce067150..15fdaa539f1 100644
--- a/gcc/config/riscv/zicond.md
+++ b/gcc/config/riscv/zicond.md
@@ -98,3 +98,48 @@ (define_split
operands[6] = gen_rtx_fmt_ee (GET_CODE (operands[1]) == LE ? GT : GTU,
<X:MODE>mode, operands[2], operands[3]);
})
+
+;; Users might use explicit arithmetic operations to create a mask and
+;; then and it, in a sequence like
+;; cond = (bits >> SHIFT) & 1;
+;; mask = ~(cond - 1);
+;; val &= mask;
+;; which will present as a single-bit sign-extract in the combiner.
+;;
+;; This will give rise to any of the following cases:
+;; - with Zbs and XVentanaCondOps: bexti + vt.maskc
+;; - with XVentanaCondOps (but w/o Zbs):
+;; - andi + vt.maskc, if the mask is representable in the immediate
+;; (which requires extra care due to the immediate
+;; being sign-extended)
+;; - slli + srli + and
+;; - otherwise: slli + srli + and
+
+;; With Zbb, we have bexti for all possible bits...
+(define_split
+ [(set (match_operand:X 0 "register_operand")
+ (and:X (sign_extract:X (match_operand:X 1 "register_operand")
+ (const_int 1)
+ (match_operand 2 "immediate_operand"))
+ (match_operand:X 3 "register_operand")))
+ (clobber (match_operand:X 4 "register_operand"))]
+ "TARGET_ZICOND && TARGET_ZBS"
+ [(set (match_dup 4) (zero_extract:X (match_dup 1) (const_int 1) (match_dup
2)))
+ (set (match_dup 0) (and:X (neg:X (ne:X (match_dup 4) (const_int 0)))
+ (match_dup 3)))])
+
+;; ...whereas RV64I only allows us access to bits 0..10 in a single andi.
+(define_split
+ [(set (match_operand:X 0 "register_operand")
+ (and:X (sign_extract:X (match_operand:X 1 "register_operand")
+ (const_int 1)
+ (match_operand 2 "immediate_operand"))
+ (match_operand:X 3 "register_operand")))
+ (clobber (match_operand:X 4 "register_operand"))]
+ "TARGET_ZICOND && !TARGET_ZBS && (UINTVAL (operands[2]) < 11)"
+ [(set (match_dup 4) (and:X (match_dup 1) (match_dup 2)))
+ (set (match_dup 0) (and:X (neg:X (ne:X (match_dup 4) (const_int 0)))
+ (match_dup 3)))]
+{
+ operands[2] = GEN_INT(1 << UINTVAL(operands[2]));
+})
diff --git a/gcc/testsuite/gcc.target/riscv/zicond-le-01.c
b/gcc/testsuite/gcc.target/riscv/zicond-le-01.c
new file mode 100644
index 00000000000..e5902d1ca5b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zicond-le-01.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zicond -mabi=lp64 -mbranch-cost=4" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-O1" "-Os" "-Oz" } } */
+
+long long sink (long long);
+
+long long le1 (long long a, long long b)
+{
+ if (a <= b)
+ b = 0;
+
+ return sink(b);
+}
+
+/* { dg-final { scan-assembler-times "sgt\t" 1 } } */
+/* { dg-final { scan-assembler-times "czero.eqz\t" 1 } } */
--
2.34.1
