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[v2,4/8] RISC-V: Recognize sign-extract + and cases for XVentanaCondOps

Message ID 20221113212030.4078815-5-philipp.tomsich@vrull.eu
State New
Headers show
Series RISC-V: Backend support for XVentanaCondOps/ZiCondops | expand

Commit Message

Philipp Tomsich Nov. 13, 2022, 9:20 p.m. UTC 
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 + vt.maskc, if both Zbs and XVentanaCondOps are present
 - andi + vt.maskc, 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/xventanacondops.md: Recognize SIGN_EXTRACT
	  of a single-bit followed by AND for XVentanaCondOps.

Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
---

(no changes since v1)

 gcc/config/riscv/xventanacondops.md | 45 +++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
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Patch

diff --git a/gcc/config/riscv/xventanacondops.md b/gcc/config/riscv/xventanacondops.md
index f23058b95b2..a4068e53c13 100644
--- a/gcc/config/riscv/xventanacondops.md
+++ b/gcc/config/riscv/xventanacondops.md
@@ -74,3 +74,48 @@ 
   [(set (match_dup 5) (match_dup 1))
    (set (match_dup 0) (and:X (neg:X (ne:X (match_dup 5) (const_int 0)))
 			     (match_dup 4)))])
+
+;; 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_XVENTANACONDOPS && 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_XVENTANACONDOPS && !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]));
+})