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From: "gjl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114779] New: __builtin_constant_p does not
 work in inline functions
Date: Fri, 19 Apr 2024 08:28:39 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: gjl at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114779

            Bug ID: 114779
           Summary: __builtin_constant_p does not work in inline functions
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

Take the following C test case with a special function register (SFR)
definition at a constant address:

#define SFR (*(volatile int*) 0x100)

static __inline__ __attribute__((__always_inline__))
void test_bcp (int volatile *psfr)
{
    if (! __builtin_constant_p (psfr))
        __asm (".error \"psfr is not constant\"");
}

int main (void)
{
    test_bcp (& SFR);
    return 0;
}

Then compile with:

$ gcc bar.c -c -O2
Assembler messages:
Error: psfr is not constant=