Re: [RFC PATCH v1 06/10] RISC-V: Recognize sign-extract + and cases for czero.eqz/nez

[Jeff Law via Gcc-patches]

On 2/10/23 15:41, Philipp Tomsich wrote:

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.
Conceptually OK.  In fact using bext to drive if conversions is 
something I think we've got in our queue of things to investigate here. 
So you may have just made Raphael's work easier ;-)


As with the other patches we just need to adjust to using the 
if-then-else form.   You've got a mention of XVentanaCondOps in the 
comments, you might want to change that to zicond.



jeff

[RFC PATCH v1 06/10] RISC-V: Recognize sign-extract + and cases for czero.eqz/nez

[Philipp Tomsich]

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 
---

 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,
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 000..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