powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()

powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()

At the time being, __put_user()/__get_user() and friends only use
D-form addressing, with 0 offset. Ex:

	lwz	reg1, 0(reg2)

Give the compiler the opportunity to use other adressing modes
whenever possible, to get more optimised code.

Hereunder is a small exemple:

struct test {
	u32 item1;
	u16 item2;
	u8 item3;
	u64 item4;
};

int set_test_user(struct test __user *from, struct test __user *to)
{
	int err;
	u32 item1;
	u16 item2;
	u8 item3;
	u64 item4;

	err = __get_user(item1, &from->item1);
	err |= __get_user(item2, &from->item2);
	err |= __get_user(item3, &from->item3);
	err |= __get_user(item4, &from->item4);

	err |= __put_user(item1, &to->item1);
	err |= __put_user(item2, &to->item2);
	err |= __put_user(item3, &to->item3);
	err |= __put_user(item4, &to->item4);

	return err;
}

Before the patch:

00000df0 <set_test_user>:
 df0:	94 21 ff f0 	stwu    r1,-16(r1)
 df4:	39 40 00 00 	li      r10,0
 df8:	93 c1 00 08 	stw     r30,8(r1)
 dfc:	93 e1 00 0c 	stw     r31,12(r1)
 e00:	7d 49 53 78 	mr      r9,r10
 e04:	80 a3 00 00 	lwz     r5,0(r3)
 e08:	38 e3 00 04 	addi    r7,r3,4
 e0c:	7d 46 53 78 	mr      r6,r10
 e10:	a0 e7 00 00 	lhz     r7,0(r7)
 e14:	7d 29 33 78 	or      r9,r9,r6
 e18:	39 03 00 06 	addi    r8,r3,6
 e1c:	7d 46 53 78 	mr      r6,r10
 e20:	89 08 00 00 	lbz     r8,0(r8)
 e24:	7d 29 33 78 	or      r9,r9,r6
 e28:	38 63 00 08 	addi    r3,r3,8
 e2c:	7d 46 53 78 	mr      r6,r10
 e30:	83 c3 00 00 	lwz     r30,0(r3)
 e34:	83 e3 00 04 	lwz     r31,4(r3)
 e38:	7d 29 33 78 	or      r9,r9,r6
 e3c:	7d 43 53 78 	mr      r3,r10
 e40:	90 a4 00 00 	stw     r5,0(r4)
 e44:	7d 29 1b 78 	or      r9,r9,r3
 e48:	38 c4 00 04 	addi    r6,r4,4
 e4c:	7d 43 53 78 	mr      r3,r10
 e50:	b0 e6 00 00 	sth     r7,0(r6)
 e54:	7d 29 1b 78 	or      r9,r9,r3
 e58:	38 e4 00 06 	addi    r7,r4,6
 e5c:	7d 43 53 78 	mr      r3,r10
 e60:	99 07 00 00 	stb     r8,0(r7)
 e64:	7d 23 1b 78 	or      r3,r9,r3
 e68:	38 84 00 08 	addi    r4,r4,8
 e6c:	93 c4 00 00 	stw     r30,0(r4)
 e70:	93 e4 00 04 	stw     r31,4(r4)
 e74:	7c 63 53 78 	or      r3,r3,r10
 e78:	83 c1 00 08 	lwz     r30,8(r1)
 e7c:	83 e1 00 0c 	lwz     r31,12(r1)
 e80:	38 21 00 10 	addi    r1,r1,16
 e84:	4e 80 00 20 	blr

After the patch:

00000dbc <set_test_user>:
 dbc:	39 40 00 00 	li      r10,0
 dc0:	7d 49 53 78 	mr      r9,r10
 dc4:	80 03 00 00 	lwz     r0,0(r3)
 dc8:	7d 48 53 78 	mr      r8,r10
 dcc:	a1 63 00 04 	lhz     r11,4(r3)
 dd0:	7d 29 43 78 	or      r9,r9,r8
 dd4:	7d 48 53 78 	mr      r8,r10
 dd8:	88 a3 00 06 	lbz     r5,6(r3)
 ddc:	7d 29 43 78 	or      r9,r9,r8
 de0:	7d 48 53 78 	mr      r8,r10
 de4:	80 c3 00 08 	lwz     r6,8(r3)
 de8:	80 e3 00 0c 	lwz     r7,12(r3)
 dec:	7d 29 43 78 	or      r9,r9,r8
 df0:	7d 43 53 78 	mr      r3,r10
 df4:	90 04 00 00 	stw     r0,0(r4)
 df8:	7d 29 1b 78 	or      r9,r9,r3
 dfc:	7d 43 53 78 	mr      r3,r10
 e00:	b1 64 00 04 	sth     r11,4(r4)
 e04:	7d 29 1b 78 	or      r9,r9,r3
 e08:	7d 43 53 78 	mr      r3,r10
 e0c:	98 a4 00 06 	stb     r5,6(r4)
 e10:	7d 23 1b 78 	or      r3,r9,r3
 e14:	90 c4 00 08 	stw     r6,8(r4)
 e18:	90 e4 00 0c 	stw     r7,12(r4)
 e1c:	7c 63 53 78 	or      r3,r3,r10
 e20:	4e 80 00 20 	blr

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c27bc4e598daf3bbb225de7a1f5c52121cf1e279.1597235091.git.christophe.leroy@csgroup.eu