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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/100056] [9/10/11 Regression]  orr + lsl vs. [us]bfiz
Date: Tue, 13 Apr 2021 10:55:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100056

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, the change is that previously there was just one significant combinatio=
n,
Trying 7 -> 8:
    7: r96:SI=3Dr94:SI<<0xb
    8: r95:SI=3Dr96:SI|r94:SI
      REG_DEAD r96:SI
      REG_DEAD r94:SI
Successfully matched this instruction:
(set (reg:SI 95)
    (ior:SI (ashift:SI (reg/v:SI 94 [ i ])
            (const_int 11 [0xb]))
        (reg/v:SI 94 [ i ])))
With the addition of 2 to 2 combination,
Trying 2 -> 7:
    2: r94:SI=3Dzero_extend(x0:QI)
      REG_DEAD x0:QI
    7: r96:SI=3Dr94:SI<<0xb
is replaced with:
(set (reg/v:SI 94 [ i ])
    (zero_extend:SI (reg:QI 0 x0 [ i ])))
and
(set (reg:SI 96)
    (and:SI (ashift:SI (reg:SI 0 x0 [ i ])
            (const_int 11 [0xb]))
        (const_int 522240 [0x7f800])))
and therefore the combination that was successful earlier no longer trigger=
s.
So, I think it would be helpful to have a combiner splitter that would split
Trying 7, 2 -> 8:
    7: r96:SI=3Dx0:SI<<0xb&0x7f800
      REG_DEAD x0:QI
    2: r94:SI=3Dzero_extend(x0:QI)
    8: r95:SI=3Dr96:SI|r94:SI
the zero_extend and
(set (reg:SI 95)
    (ior:SI (ashift:SI (reg/v:SI 94 [ i ])
            (const_int 11 [0xb]))
        (reg/v:SI 94 [ i ])))=