[LLVMbugs] [Bug 6282] New: Multiple inclusion elimination is too aggressive

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=6282

           Summary: Multiple inclusion elimination is too aggressive
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: preprocessor
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: dgregor at apple.com
                CC: llvmbugs at cs.uiuc.edu
            Blocks: 6023


In the following example, Clang's multiple-inclusion detection is suppressing
the second inclusion of "t.h", so we get different results from GCC. This
actually manifests itself in a Boost bug, since Boost often uses "vertical
repetition" (i.e., including the same file many times with different macro
definitions) for its preprocessor metaprogramming.

terfin:Projects dgregor$ cat t.h
#ifndef ITERATING
void NAME(int) { }
#else
void NAME(int) { }
#endif
terfin:Projects dgregor$ cat t.c
#define ITERATING 1
#define NAME foo
#include "t.h"
#include "t.h"

# 1 "t.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "t.c"


# 1 "t.h" 1



void foo(int) { }
# 4 "t.c" 2
# 1 "t.h" 1



void foo(int) { }
# 5 "t.c" 2

# 1 "t.c"
# 1 "t.c" 1
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 120 "<built-in>" 3
# 120 "<command line>" 1
# 121 "<built-in>" 2
# 1 "t.c" 2


# 1 "./t.h" 1



void foo(int) { }
# 4 "t.c" 2


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