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From: "lis8215 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/111835] New: Suboptimal codegen: zero extended load
 instead of sign extended one
Date: Mon, 16 Oct 2023 14:46:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111835

            Bug ID: 111835
           Summary: Suboptimal codegen: zero extended load instead of sign
                    extended one
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lis8215 at gmail dot com
  Target Milestone: ---

In this simplified example:

int test (const uint8_t * src, uint8_t * dst)
{
    int8_t tmp =3D (int8_t)*src;
    *dst =3D tmp;
    return tmp;
}

GCC prefers to use load with zero extension instead of more rational sign
extended load.
Then it needs to do explicit sign extension for making return value.

I know there's a lot of bugs related to zero/sign ext, but I guessed it's r=
are
special case, and it reproduces in any GCC version available at godbolt and=
 any
architecture except x86-64.=