[PATCH v7 03/12] RISC-V: Add CRC expander to generate faster CRC.

If the target is ZBC or ZBKC, it uses clmul instruction for the CRC
calculation.  Otherwise, if the target is ZBKB, generates table-based
CRC, but for reversing inputs and the output uses bswap and brev8
instructions.  Add new tests to check CRC generation for ZBC, ZBKC and
ZBKB targets.

gcc/

	* expr.cc (gf2n_poly_long_div_quotient): New function.
	* expr.h (gf2n_poly_long_div_quotient):  New function declaration.
	* hwint.cc (reflect_hwi): New function.
	* hwint.h (reflect_hwi): New function declaration.
	* config/riscv/bitmanip.md (crc_rev<ANYI1:mode><ANYI:mode>4): New
	expander for reversed CRC.
	(crc<SUBX1:mode><SUBX:mode>4): New expander for bit-forward CRC.
	* config/riscv/iterators.md (SUBX1, ANYI1): New iterators.
	* config/riscv/riscv-protos.h (generate_reflecting_code_using_brev):
	New function declaration.
	(expand_crc_using_clmul): Likewise.
	(expand_reversed_crc_using_clmul): Likewise.
	* config/riscv/riscv.cc (generate_reflecting_code_using_brev): New
	function.
	(expand_crc_using_clmul): Likewise.
	(expand_reversed_crc_using_clmul): Likewise.
	* config/riscv/riscv.md (UNSPEC_CRC, UNSPEC_CRC_REV):  New unspecs.

	* doc/sourcebuild.texi: Document new target selectors.

gcc/testsuite
	* lib/target-supports.exp (check_effective_target_riscv_zbc): New
	target supports predicate.
	(check_effective_target_riscv_zbkb): Likewise.
	(check_effective_target_riscv_zbkc): Likewise.
	(check_effective_target_zbc_ok): Likewise.
	(check_effective_target_zbkb_ok): Likewise.
	(check_effective_target_zbkc_ok): Likewise.
	(riscv_get_arch): Add zbkb and zbkc support.

	* gcc.target/riscv/crc-builtin-zbc32.c: New file.
	* gcc.target/riscv/crc-builtin-zbc64.c: Likewise.

	    Co-author: Jeff Law  <jlaw@ventanamicro.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/gcc/expr.cc b/gcc/expr.cc
index de25437..70f2ece 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -14178,6 +14178,33 @@ int_expr_size (const_tree exp)
   return tree_to_shwi (size);
 }
 
+/* Return the quotient of polynomial long division of x^2N by POLYNOMIAL
+   in GF (2^N).
+   Author: Richard Sandiford <richard.sandiford@arm.com>  */
+
+unsigned HOST_WIDE_INT
+gf2n_poly_long_div_quotient (unsigned HOST_WIDE_INT polynomial,
+			     unsigned short n)
+{
+  /* The result has degree N, so needs N + 1 bits.  */
+  gcc_assert (n < 64);
+
+  /* Perform a division step for the x^2N coefficient.  At this point the
+     quotient and remainder have N implicit trailing zeros.  */
+  unsigned HOST_WIDE_INT quotient = 1;
+  unsigned HOST_WIDE_INT remainder = polynomial;
+
+  /* Process the coefficients for x^(2N-1) down to x^N, with each step
+     reducing the number of implicit trailing zeros by one.  */
+  for (unsigned int i = 0; i < n; ++i)
+    {
+      bool coeff = remainder & (HOST_WIDE_INT_1U << (n - 1));
+      quotient = (quotient << 1) | coeff;
+      remainder = (remainder << 1) ^ (coeff ? polynomial : 0);
+    }
+  return quotient;
+}
+
 /* Calculate CRC for the initial CRC and given POLYNOMIAL.
    CRC_BITS is CRC size.  */