MIPS: Add pattern insqisi_extended and inshisi_extended

This match pattern allows combination (zero_extract:DI 8, 24, QI)
with an sign-extend to 32bit INS instruction on TARGET_64BIT.

For SI mode, if the sign-bit is modified by bitops, we will need a
sign-extend operation.  Since 32bit INS instruction can be sure that
result is sign-extended, and the QImode src register is safe for INS, too.

(insn 19 18 20 2 (set (zero_extract:DI (reg/v:DI 200 [ val ])
            (const_int 8 [0x8])
            (const_int 24 [0x18]))
        (subreg:DI (reg:QI 205) 0)) "../xx.c":7:29 -1
     (nil))
(insn 20 19 23 2 (set (reg/v:DI 200 [ val ])
        (sign_extend:DI (subreg:SI (reg/v:DI 200 [ val ]) 0))) "../xx.c":7:29 -1
     (nil))

Combine try to merge them to:

(insn 20 19 23 2 (set (reg/v:DI 200 [ val ])
        (sign_extend:DI (ior:SI (and:SI (subreg:SI (reg/v:DI 200 [ val ]) 0)
                    (const_int 16777215 [0xffffff]))
                (ashift:SI (subreg:SI (reg:QI 205 [ MEM[(const unsigned char *)buf_8(D) + 3B] ]) 0)
                    (const_int 24 [0x18]))))) "../xx.c":7:29 18 {*insv_extended}
     (expr_list:REG_DEAD (reg:QI 205 [ MEM[(const unsigned char *)buf_8(D) + 3B] ])
        (nil)))

And do similarly for 16/16 pair:
(insn 13 12 14 2 (set (zero_extract:DI (reg/v:DI 198 [ val ])
            (const_int 16 [0x10])
            (const_int 16 [0x10]))
        (subreg:DI (reg:HI 201 [ MEM[(const short unsigned int *)buf_6(D) + 2B] ]) 0)) "xx.c":5:30 286 {*insvdi}
     (expr_list:REG_DEAD (reg:HI 201 [ MEM[(const short unsigned int *)buf_6(D) + 2B] ])
        (nil)))
(insn 14 13 17 2 (set (reg/v:DI 198 [ val ])
        (sign_extend:DI (subreg:SI (reg/v:DI 198 [ val ]) 0))) "xx.c":5:30 241 {extendsidi2}
     (nil))
------------>
(insn 14 13 17 2 (set (reg/v:DI 198 [ val ])
        (sign_extend:DI (ior:SI (ashift:SI (subreg:SI (reg:HI 201 [ MEM[(const short unsigned int *)buf_6(D) + 2B] ]) 0)
                    (const_int 16 [0x10]))
                (zero_extend:SI (subreg:HI (reg/v:DI 198 [ val ]) 0))))) "xx.c":5:30 284 {*inshisi_extended}
     (expr_list:REG_DEAD (reg:HI 201 [ MEM[(const short unsigned int *)buf_6(D) + 2B] ])
        (nil)))

Let's accept these patterns, and set the cost to 1 instruction.

gcc

	PR rtl-optimization/104914
	* config/mips/mips.md (insqisi_extended): New patterns.
	(inshisi_extended): Ditto.

gcc/testsuite

	* gcc.target/mips/pr104914.c: New test.