[PATCH] Wrong output from built-in size function

[Nuno Lopes]

Hi,

I don't think this is the right fix.
On that file, lines 1512-1515, and after calling isAllocSiteRemovable(), the 
objectsize intrinsic is replaced with the "don't know" value.  Which is 
fine, semantics wise, but we can do better as you expect.
I think that at that point we could try to infer the size of the object, and 
only resort to the don't know value if we fail. Take a look at the 
getObjectSize() function, and InstCombineCalls.cpp for an example usage.

Nuno

P.S.: BTW, this patch is not for clang, so please send the new version to 
llvm-commits.

----- Original Message ----- 
From: "MAYUR PANDEY" <mayur.p at samsung.com>
To: <cfe-commits at cs.uiuc.edu>
Sent: Tuesday, March 18, 2014 8:19 AM
Subject: [PATCH] Wrong output from built-in size function


> Hi,
>
> Please find attached the fix for wrong output from built-in size function. 
> The Testcase attached is a standard gcc testsuite TC.
>
>
>
> extern void abort (void);
>
> extern inline __attribute__ ((__always_inline__)) int
> foo (char *dest)
> {
>  return __builtin_object_size (dest, 1);
> }
>
> struct S
> {
>  union
>  {
>    struct { int a, b; char c, d; } f;
>    struct { struct { int a, b; char c, d[255]; } e; } g;
>  } u;
> };
>
> int
> main (void)
> {
>  struct S s;
>  if (foo (s.u.g.e.d) != 255)
>    abort ();
>  return 0;
> }
>
>
>
> In the TC above the abort function is called as clang is unable to return 
> correct output on calling built-in size function. the reason seems to be 
> that in Instruction Combination pass for optimization,
>
> Clang was not able to properly handle built-in size function as per new 
> DFS implementation. So Moving it back to follow iterative way specifically 
> for built-in size function.
>
>
>
> Please Review.
>
>
>
> Thanks,
>
> Mayur