MATCH: Optimize COND_ADD_LEN reduction pattern

MATCH: Optimize COND_ADD_LEN reduction pattern

This patch leverage this commit: https://gcc.gnu.org/git/gitweb.cgi?p=gcc.git;h=62b505a4d5fc89
to optimize COND_LEN_ADD reduction pattern.

We are doing optimization of VEC_COND_EXPR + COND_LEN_ADD -> COND_LEN_ADD.

Consider thsi following case:

void
pr11594 (uint64_t *restrict a, uint64_t *restrict b, int loop_size)
{
  uint64_t result = 0;

  for (int i = 0; i < loop_size; i++)
    {
      if (b[i] <= a[i])
	{
	  result += a[i];
	}
    }

  a[0] = result;
}

Before this patch:
        vsetvli a7,zero,e64,m1,ta,ma
        vmv.v.i v2,0
        vmv1r.v v3,v2                    --- redundant
.L3:
        vsetvli a5,a2,e64,m1,ta,ma
        vle64.v v1,0(a3)
        vle64.v v0,0(a1)
        slli    a6,a5,3
        vsetvli a7,zero,e64,m1,ta,ma
        sub     a2,a2,a5
        vmsleu.vv       v0,v0,v1
        add     a1,a1,a6
        vmerge.vvm      v1,v3,v1,v0     ---- redundant.
        add     a3,a3,a6
        vsetvli zero,a5,e64,m1,tu,ma
        vadd.vv v2,v2,v1
        bne     a2,zero,.L3
        li      a5,0
        vsetvli a4,zero,e64,m1,ta,ma
        vmv.s.x v1,a5
        vredsum.vs      v2,v2,v1
        vmv.x.s a5,v2
        sd      a5,0(a0)
        ret

After this patch:

	vsetvli	a6,zero,e64,m1,ta,ma
	vmv.v.i	v1,0
.L3:
	vsetvli	a5,a2,e64,m1,ta,ma
	vle64.v	v2,0(a4)
	vle64.v	v0,0(a1)
	slli	a3,a5,3
	vsetvli	a6,zero,e64,m1,ta,ma
	sub	a2,a2,a5
	vmsleu.vv	v0,v0,v2
	add	a1,a1,a3
	vsetvli	zero,a5,e64,m1,tu,mu
	add	a4,a4,a3
	vadd.vv	v1,v1,v2,v0.t
	bne	a2,zero,.L3
	li	a5,0
	vsetivli	zero,1,e64,m1,ta,ma
	vmv.s.x	v2,a5
	vsetvli	a5,zero,e64,m1,ta,ma
	vredsum.vs	v1,v1,v2
	vmv.x.s	a5,v1
	sd	a5,0(a0)
	ret

Bootstrap && Regression is running.

Ok for trunk when testing passes ?

	PR tree-optimization/111594
	PR tree-optimization/110660

gcc/ChangeLog:

	* match.pd: Optimize COND_LEN_ADD reduction.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/cond/cond_reduc-1.c: New test.
	* gcc.target/riscv/rvv/autovec/cond/pr111594.c: New test.