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From: "dcb314 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/103920] New: No warning for large structs passed by value ?
Date: Wed, 05 Jan 2022 16:48:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103920

            Bug ID: 103920
           Summary: No warning for large structs passed by value ?
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com
  Target Milestone: ---

For the following code:

$ more jan5c.cc

struct S
{
        long a;
        long b;
        long c;
        long d;
        long a2;
        long b2;
        long c2;
        long d2;
};

void f1( const S s);
void f2( S s);

gcc has not a lot to say:

$ /home/dcb/gcc/results/bin/gcc -c -O2 -Wall -Wextra -pedantic jan5c.cc
$

cppcheck does a slightly better job:

$ /home/dcb/cppcheck/trunk.git/cppcheck --enable=3Dall jan5c.cc
jan5c.cc:14:18: performance: Function parameter 's' should be passed by con=
st
reference. [passedByValue]
void f1( const S s);
                 ^
Also, clang-13 doesn't say anything.=20

Judgement call, but "large" might mean four words or more.=20

Example code derived from code in the Linux kernel, so even kernel programm=
ers
do this kind of thing in practice.=