bfin: Popcount-related improvements to machine description.

Blackfin processors support a ONES instruction that implements a
32-bit popcount returning a 16-bit result.  This instruction was
previously described by GCC's bfin backend using an UNSPEC, which
this patch changes to use a popcount:SI rtx thats capture its semantics,
allowing it to evaluated and simplified at compile-time.  I've decided
to keep the instruction name the same (avoiding any changes to the
__builtin_bfin_ones machinery), but have provided popcountsi2 and
popcounthi2 expanders so that the middle-end can use this instruction
to implement __builtin_popcount (and __builtin_parity).

The new testcase ones.c
short foo ()
{
  int t = 5;
  short r = __builtin_bfin_ones(t);
  return r;
}

previously generated:
_foo:   nop;
        nop;
        R0 = 5 (X);
        R0.L = ONES R0;
        rts;

with this patch, now generates:
_foo:   nop;
        nop;
        nop;
        R0 = 2 (X);
        rts;

The new testcase popcount.c
int foo(int x)
{
  return __builtin_popcount(x);
}

previously generated:
_foo:   [--SP] = RETS;
        SP += -12;
        call ___popcountsi2;
        SP += 12;
        RETS = [SP++];
        rts;

now generates:
_foo:   nop;
        nop;
        R0.L = ONES R0;
        R0 = R0.L (Z);
        rts;

And the new testcase parity.c
int foo(int x)
{
  return __builtin_parity(x);
}

previously generated:
_foo:	[--SP] = RETS;
        SP += -12;
        call ___paritysi2;
        SP += 12;
        RETS = [SP++];
        rts;

now generates:
_foo:	nop;
        R1 = 1 (X);
        R0.L = ONES R0;
        R0 = R1 & R0;
        rts;

2021-10-18  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/bfin/bfin.md (define_constants): Remove UNSPEC_ONES.
	(define_insn "ones"): Replace UNSPEC_ONES with a truncate of
	a popcount, allowing compile-time evaluation/simplification.
	(popcountsi2, popcounthi2): New expanders using a "ones" insn.

gcc/testsuite/ChangeLog
	* gcc.target/bfin/ones.c: New test case.
	* gcc.target/bfin/parity.c: New test case.
	* gcc.target/bfin/popcount.c: New test case.

gcc/config/bfin/bfin.md

@@ -138,8 +138,7 @@
    ;; Distinguish a 32-bit version of an insn from a 16-bit version.
    (UNSPEC_32BIT 11)
    (UNSPEC_NOP 12)
-   (UNSPEC_ONES 13)
-   (UNSPEC_ATOMIC 14)])
+   (UNSPEC_ATOMIC 13)])
 
 (define_constants
   [(UNSPEC_VOLATILE_CSYNC 1)
@@ -1398,12 +1397,32 @@
 
 (define_insn "ones"
   [(set (match_operand:HI 0 "register_operand" "=d")
-	(unspec:HI [(match_operand:SI 1 "register_operand" "d")]
-		UNSPEC_ONES))]
+	(truncate:HI
+	 (popcount:SI (match_operand:SI 1 "register_operand" "d"))))]
   ""
   "%h0 = ONES %1;"
   [(set_attr "type" "alu0")])
 
+(define_expand "popcountsi2"
+  [(set (match_dup 2)
+	(truncate:HI (popcount:SI (match_operand:SI 1 "register_operand" ""))))
+   (set (match_operand:SI 0 "register_operand")
+	(zero_extend:SI (match_dup 2)))]
+  ""
+{
+  operands[2] = gen_reg_rtx (HImode);
+})
+
+(define_expand "popcounthi2"
+  [(set (match_dup 2)
+	(zero_extend:SI (match_operand:HI 1 "register_operand" "")))
+   (set (match_operand:HI 0 "register_operand") 
+	(truncate:HI (popcount:SI (match_dup 2))))]
+  ""
+{
+  operands[2] = gen_reg_rtx (SImode);
+})
+
 (define_insn "smaxsi3"
   [(set (match_operand:SI 0 "register_operand" "=d")
 	(smax:SI (match_operand:SI 1 "register_operand" "d")

gcc/testsuite/gcc.target/bfin/ones.c

@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+short foo ()
+{
+  int t = 5;
+  short r = __builtin_bfin_ones(t);
+  return r;
+}
+
+/* { dg-final { scan-assembler-not "ONES" } } */

gcc/testsuite/gcc.target/bfin/parity.c

@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int foo(int x)
+{
+  return __builtin_parity(x);
+}
+
+/* { dg-final { scan-assembler "ONES" } } */

gcc/testsuite/gcc.target/bfin/popcount.c

@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+int foo(int x)
+{
+  return __builtin_popcount(x);
+}
+
+/* { dg-final { scan-assembler "ONES" } } */