RISC-V: Support movmisalign of RVV VLA modes

This patch fixed these following FAILs in regressions:
FAIL: gcc.dg/vect/slp-perm-11.c -flto -ffat-lto-objects  scan-tree-dump-times vect "vectorizing stmts using SLP" 1
FAIL: gcc.dg/vect/slp-perm-11.c scan-tree-dump-times vect "vectorizing stmts using SLP" 1
FAIL: gcc.dg/vect/vect-bitfield-read-2.c -flto -ffat-lto-objects  scan-tree-dump-not optimized "Invalid sum"
FAIL: gcc.dg/vect/vect-bitfield-read-2.c scan-tree-dump-not optimized "Invalid sum"
FAIL: gcc.dg/vect/vect-bitfield-read-4.c -flto -ffat-lto-objects  scan-tree-dump-not optimized "Invalid sum"
FAIL: gcc.dg/vect/vect-bitfield-read-4.c scan-tree-dump-not optimized "Invalid sum"
FAIL: gcc.dg/vect/vect-bitfield-write-2.c -flto -ffat-lto-objects  scan-tree-dump-not optimized "Invalid sum"
FAIL: gcc.dg/vect/vect-bitfield-write-2.c scan-tree-dump-not optimized "Invalid sum"
FAIL: gcc.dg/vect/vect-bitfield-write-3.c -flto -ffat-lto-objects  scan-tree-dump-not optimized "Invalid sum"
FAIL: gcc.dg/vect/vect-bitfield-write-3.c scan-tree-dump-not optimized "Invalid sum"

Previously, I removed the movmisalign pattern to fix the execution FAILs in this commit:
https://github.com/gcc-mirror/gcc/commit/f7bff24905a6959f85f866390db2fff1d6f95520

I was thinking that RVV doesn't allow misaligned at the beginning so I removed that pattern.
However, after deep investigation && reading RVV ISA again and experiment on SPIKE,
I realized I was wrong.

RVV ISA reference: https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc#vector-memory-alignment-constraints

"If an element accessed by a vector memory instruction is not naturally aligned to the size of the element,
 either the element is transferred successfully or an address misaligned exception is raised on that element."

It's obvious that RVV ISA does allow misaligned vector load/store.

And experiment and confirm on SPIKE:

[jzzhong@rios-cad122:/work/home/jzzhong/work/toolchain/riscv/gcc/gcc/testsuite/gcc.dg/vect]$~/work/toolchain/riscv/build/dev-rv64gcv_zfh-lp64d-medany-newlib-spike-debug/install/bin/spike --isa=rv64gcv --varch=vlen:128,elen:64 ~/work/toolchain/riscv/build/dev-rv64gcv_zfh-lp64d-medany-newlib-spike-debug/install/riscv64-unknown-elf/bin/pk64  a.out
bbl loader
z  0000000000000000 ra 0000000000010158 sp 0000003ffffffb40 gp 0000000000012c48
tp 0000000000000000 t0 00000000000110da t1 000000000000000f t2 0000000000000000
s0 0000000000013460 s1 0000000000000000 a0 0000000000012ef5 a1 0000000000012018
a2 0000000000012a71 a3 000000000000000d a4 0000000000000004 a5 0000000000012a71
a6 0000000000012a71 a7 0000000000012018 s2 0000000000000000 s3 0000000000000000
s4 0000000000000000 s5 0000000000000000 s6 0000000000000000 s7 0000000000000000
s8 0000000000000000 s9 0000000000000000 sA 0000000000000000 sB 0000000000000000
t3 0000000000000000 t4 0000000000000000 t5 0000000000000000 t6 0000000000000000
pc 0000000000010258 va/inst 00000000020660a7 sr 8000000200006620
Store/AMO access fault!

[jzzhong@rios-cad122:/work/home/jzzhong/work/toolchain/riscv/gcc/gcc/testsuite/gcc.dg/vect]$~/work/toolchain/riscv/build/dev-rv64gcv_zfh-lp64d-medany-newlib-spike-debug/install/bin/spike --misaligned --isa=rv64gcv --varch=vlen:128,elen:64 ~/work/toolchain/riscv/build/dev-rv64gcv_zfh-lp64d-medany-newlib-spike-debug/install/riscv64-unknown-elf/bin/pk64  a.out
bbl loader

We can see SPIKE can pass previous *FAILED* execution tests with specifying --misaligned to SPIKE.

So, to honor RVV ISA SPEC, we should add movmisalign pattern back base on the investigations I have done since
it can improve multiple vectorization tests and fix dumple FAILs.

This patch adds TARGET_VECTOR_MISALIGN_SUPPORTED to decide whether we support misalign pattern for VLA modes (By default it is enabled).

Consider this following case:

struct s {
    unsigned i : 31;
    char a : 4;
};

#define N 32
#define ELT0 {0x7FFFFFFFUL, 0}
#define ELT1 {0x7FFFFFFFUL, 1}
#define ELT2 {0x7FFFFFFFUL, 2}
#define ELT3 {0x7FFFFFFFUL, 3}
#define RES 48
struct s A[N]
  = { ELT0, ELT1, ELT2, ELT3, ELT0, ELT1, ELT2, ELT3,
      ELT0, ELT1, ELT2, ELT3, ELT0, ELT1, ELT2, ELT3,
      ELT0, ELT1, ELT2, ELT3, ELT0, ELT1, ELT2, ELT3,
      ELT0, ELT1, ELT2, ELT3, ELT0, ELT1, ELT2, ELT3};

int __attribute__ ((noipa))
f(struct s *ptr, unsigned n) {
    int res = 0;
    for (int i = 0; i < n; ++i)
      res += ptr[i].a;
    return res;
}

-O3 -S -fno-vect-cost-model (default strict-align):

f:
	mv	a4,a0
	beq	a1,zero,.L9
	addiw	a5,a1,-1
	li	a3,14
	vsetivli	zero,16,e64,m8,ta,ma
	bleu	a5,a3,.L3
	andi	a5,a0,127
	bne	a5,zero,.L3
	srliw	a3,a1,4
	slli	a3,a3,7
	li	a0,15
	slli	a0,a0,32
	add	a3,a3,a4
	mv	a5,a4
	li	a2,32
	vmv.v.x	v16,a0
	vsetvli	zero,zero,e32,m4,ta,ma
	vmv.v.i	v4,0
.L4:
	vsetvli	zero,zero,e64,m8,ta,ma
	vle64.v	v8,0(a5)
	addi	a5,a5,128
	vand.vv	v8,v8,v16
	vsetvli	zero,zero,e32,m4,ta,ma
	vnsrl.wx	v8,v8,a2
	vadd.vv	v4,v4,v8
	bne	a5,a3,.L4
	li	a3,0
	andi	a5,a1,15
	vmv.s.x	v1,a3
	andi	a3,a1,-16
	vredsum.vs	v1,v4,v1
	vmv.x.s	a0,v1
	mv	a2,a0
	beq	a5,zero,.L15
	slli	a5,a3,3
	add	a5,a4,a5
	lw	a0,4(a5)
	andi	a0,a0,15
	addiw	a4,a3,1
	addw	a0,a0,a2
	bgeu	a4,a1,.L15
	lw	a2,12(a5)
	andi	a2,a2,15
	addiw	a4,a3,2
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a2,20(a5)
	andi	a2,a2,15
	addiw	a4,a3,3
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a2,28(a5)
	andi	a2,a2,15
	addiw	a4,a3,4
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a2,36(a5)
	andi	a2,a2,15
	addiw	a4,a3,5
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a2,44(a5)
	andi	a2,a2,15
	addiw	a4,a3,6
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a2,52(a5)
	andi	a2,a2,15
	addiw	a4,a3,7
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a4,60(a5)
	andi	a4,a4,15
	addw	a4,a4,a0
	addiw	a2,a3,8
	mv	a0,a4
	bgeu	a2,a1,.L15
	lw	a0,68(a5)
	andi	a0,a0,15
	addiw	a2,a3,9
	addw	a0,a0,a4
	bgeu	a2,a1,.L15
	lw	a2,76(a5)
	andi	a2,a2,15
	addiw	a4,a3,10
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a2,84(a5)
	andi	a2,a2,15
	addiw	a4,a3,11
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a2,92(a5)
	andi	a2,a2,15
	addiw	a4,a3,12
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a2,100(a5)
	andi	a2,a2,15
	addiw	a4,a3,13
	addw	a0,a2,a0
	bgeu	a4,a1,.L15
	lw	a4,108(a5)
	andi	a4,a4,15
	addiw	a3,a3,14
	addw	a0,a4,a0
	bgeu	a3,a1,.L15
	lw	a5,116(a5)
	andi	a5,a5,15
	addw	a0,a5,a0
	ret
.L9:
	li	a0,0
.L15:
	ret
.L3:
	mv	a5,a4
	slli	a4,a1,32
	srli	a1,a4,29
	add	a1,a5,a1
	li	a0,0
.L7:
	lw	a4,4(a5)
	andi	a4,a4,15
	addi	a5,a5,8
	addw	a0,a4,a0
	bne	a5,a1,.L7
	ret

-O3 -S -mno-strict-align -fno-vect-cost-model:

f:
	beq	a1,zero,.L4
	slli	a1,a1,32
	li	a5,15
	vsetvli	a4,zero,e64,m1,ta,ma
	slli	a5,a5,32
	srli	a1,a1,32
	li	a6,32
	vmv.v.x	v3,a5
	vsetvli	zero,zero,e32,mf2,ta,ma
	vmv.v.i	v2,0
.L3:
	vsetvli	a5,a1,e64,m1,ta,ma
	vle64.v	v1,0(a0)
	vsetvli	a3,zero,e64,m1,ta,ma
	slli	a2,a5,3
	vand.vv	v1,v1,v3
	sub	a1,a1,a5
	vsetvli	zero,zero,e32,mf2,ta,ma
	add	a0,a0,a2
	vnsrl.wx	v1,v1,a6
	vsetvli	zero,a5,e32,mf2,tu,ma
	vadd.vv	v2,v2,v1
	bne	a1,zero,.L3
	li	a5,0
	vsetvli	a3,zero,e32,mf2,ta,ma
	vmv.s.x	v1,a5
	vredsum.vs	v2,v2,v1
	vmv.x.s	a0,v2
	ret
.L4:
	li	a0,0
	ret

We can see it improves this case codegen a lot.

gcc/ChangeLog:

	* config/riscv/riscv-opts.h (TARGET_VECTOR_MISALIGN_SUPPORTED): New macro.
	* config/riscv/riscv.cc (riscv_support_vector_misalignment): Depend on movmisalign pattern.
	* config/riscv/vector.md (movmisalign<mode>): New pattern.