[llvm-bugs] [Bug 25955] New: [C standard violation] incorrect value of a variable pointer to a constant value after a recursive function call

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25955

            Bug ID: 25955
           Summary: [C standard violation] incorrect value of a variable
                    pointer to a constant value after a recursive function
                    call
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: andrey.kuleshov at intel.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

-! this bug seems to be a violation of C standard 
(6.2.4 Storage durations of objects paragraph 6):
"If the block is entered recursively, a new instance of the
object is created each time. The initial value of the object is indeterminate." 

--! This problem appears because clang FE transforms const int b [] =
{constant} to an "internal constant", that means that the value is showed as a
local symbol (STB_LOCAL in the case of ELF) in the object file. But this
corresponds to a "static" keyword. Because of this no new temporary objects are
created and values of pointers are equal. 
To my mind such array might be declared as "private", not "internal" in IR 

==============HOW TO REPRODUCE====================
#include <stdio.h>
int f(int x,
#ifndef OK
  const
#endif
    int *a)
{
    #ifndef OK
    const
    #endif
        int b[] = { 1, 2, 3}; // any recursive call might create
    if (!x)
    return f(1, b);                        // f is recursively called with a
const int b[] as an argument
                                           // a new temporary object might be
crated with a pointer to another address (6.2.4p6)

    printf("const int b[] (variable declared in function): %p\n", b);
    printf("const int *a (argument of a function): %p\n", a);
    return b == a;
}

int main(void)
{
    printf("Result of f(0,0) is: %d (might be 0)\n", f(0,0));
    return 0;
}

================COMPARED TO OTHER COMPILERS=======================
>>>Microsoft cl: 
    const int b[] (variable declared in function): 000000ECFCE4FBF8
    const int *a (argument of a function): 000000ECFCE4FC48 
    Result of f(0,0) is: 0 (might be 0)

>>>Intel icc:
    const int b[] (variable declared in function): 0xffa3f9e0
    const int *a (argument of a function): 0xffa3fa80
    Result of f(0,0) is: 0 (might be 0)

>>>gcc:
    const int b[] (variable declared in function): 0x7fff8a6dfa00
    const int *a (argument of a function): 0x7fff8a6dfa30
    Result of f(0,0) is: 0 (might be 0)

>>>clang:
    const int b[] (variable declared in function): 0x400640
    const int *a (argument of a function): 0x400640
    Result of f(0,0) is: 1 (might be 0)

-------------------------
Intel Software Engineer
Andrey Kuleshov

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