[PATCH] [analyzer] Make realloc(ptr, 0) handling equivalent to malloc(0).

[Антон Ярцев]

Hi zaks.anna,

Currently realloc(ptr, 0) is treated as free() which seems to be not correct. C standard (N1570) establishes equivalent behavior for malloc(0) and realloc(ptr, 0):
"7.22.3 Memory management functions calloc, malloc, realloc: If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is  returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object."
The patch equalizes the processing of malloc(0) and realloc(ptr,0).
The patch also enables unix.Malloc checker to detect references to zero-allocated memory returned by realloc(ptr,0) ("Use of zero-allocated memory" warning).
Please review.

http://reviews.llvm.org/D9040

Files:
  lib/StaticAnalyzer/Checkers/MallocChecker.cpp
  test/Analysis/malloc-annotations.c
  test/Analysis/malloc.c

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