RISC-V: vector absolute difference expander [PR117722]

This improves codegen for x264 sum of absolute difference routines.
The insn count is same, but we avoid double widening ops and ensuing
whole register moves.

Also for more general applicability, we chose to implement abs diff
vs. the sum of abs diff variant.

Suggested-by: Robin Dapp <rdapp@ventanamicro.com>
Co-authored-by: Pan Li <pan2.li@intel.com>
Signed-off-by: Vineet Gupta <vineetg@rivosinc.com>
	PR target/117722

gcc/ChangeLog:
	* config/riscv/autovec.md: Add uabd expander.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/pr117722.c: New test.

diff --git a/gcc/config/riscv/autovec.md b/gcc/config/riscv/autovec.md
index 8d22b5f9c59a6b8dd243bed814fdf538eb1ee0c7..8426f12757f349eb7e133b4636c432f244dc97e3 100644 (file)
--- a/gcc/config/riscv/autovec.md
+++ b/gcc/config/riscv/autovec.md
@@ -2928,3 +2928,29 @@
     riscv_vector::expand_strided_store (<MODE>mode, operands);
     DONE;
   })
+
+; ========
+; == Absolute difference (not including sum)
+; ========
+(define_expand "uabd<mode>3"
+  [(match_operand:V_VLSI 0 "register_operand")
+   (match_operand:V_VLSI 1 "register_operand")
+   (match_operand:V_VLSI 2 "register_operand")]
+  "TARGET_VECTOR"
+  {
+    rtx max = gen_reg_rtx (<MODE>mode);
+    insn_code icode = code_for_pred (UMAX, <MODE>mode);
+    rtx ops1[] = {max, operands[1], operands[2]};
+    riscv_vector::emit_vlmax_insn (icode, riscv_vector::BINARY_OP, ops1);
+
+    rtx min = gen_reg_rtx (<MODE>mode);
+    icode = code_for_pred (UMIN, <MODE>mode);
+    rtx ops2[] = {min, operands[1], operands[2]};
+    riscv_vector::emit_vlmax_insn (icode, riscv_vector::BINARY_OP, ops2);
+
+    icode = code_for_pred (MINUS, <MODE>mode);
+    rtx ops3[] = {operands[0], max, min};
+    riscv_vector::emit_vlmax_insn (icode, riscv_vector::BINARY_OP, ops3);
+
+    DONE;
+  });

diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr117722.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr117722.c
new file mode 100644 (file)
index 0000000..b675930
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr117722.c
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O2" } */
+
+/* Generate sum of absolute difference as sub (max, min).
+   This helps with x264 sad routines.  */
+
+inline int abs(int i)
+{
+  return (i < 0 ? -i : i);
+}
+
+int pixel_sad_n(unsigned char *pix1, unsigned char *pix2, int n)
+{
+  int sum = 0;
+  for( int i = 0; i < n; i++ )
+       sum += abs(pix1[i] - pix2[i]);
+
+  return sum;
+}
+
+/* { dg-final { scan-assembler {vmin\.v} } } */
+/* { dg-final { scan-assembler {vmax\.v} } } */
+/* { dg-final { scan-assembler {vsub\.v} } } */