[LLVMbugs] [Bug 11641] New: preprocessor with -O2 generates incorrect warnings

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11641

             Bug #: 11641
           Summary: preprocessor with -O2 generates incorrect warnings
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: steven at ngls.net
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Created attachment 7795
  --> http://llvm.org/bugs/attachment.cgi?id=7795
unoptimized preprocessor output

Running just the prepocessor with and without -O2 generates different
output files.  The -O2 file then generates incorrect warnings.

shell log follows:

bluishred:~/work 754 ? clang -O2 -fpic -Wno-format-security -E minigzip.c >
preprocessed_O2.c 
bluishred:~/work 755 ? clang     -fpic -Wno-format-security -E minigzip.c >
preprocessed.c 
bluishred:~/work 756 ? clang     -fpic -Wno-format-security -c preprocessed.c 
bluishred:~/work 757 ? clang -O2 -fpic -Wno-format-security -c
preprocessed_O2.c 
In file included from minigzip.c:1:
minigzip.c:283:2075: warning: array index 3 is past the end of the array (which
contains 3 elements) [-Warray-bounds]
  ...- ((__const unsigned char *) (__const char *) ("-d"))[2]); if (__s2_len >
2 && __result == 0) __result = (__s1[3] - ((__const unsigned char *) (__const
char *) ("-d"))[3]); } } __result; }))) : __builtin_strcmp (*argv, "-d")))); })
== 0)
                                                                               
                                                                               
      ^      ~
minigzip.c:285:2080: warning: array index 3 is past the end of the array (which
contains 3 elements) [-Warray-bounds]
  ...- ((__const unsigned char *) (__const char *) ("-f"))[2]); if (__s2_len >
2 && __result == 0) __result = (__s1[3] - ((__const unsigned char *) (__const
char *) ("-f"))[3]); } } __result; }))) : __builtin_strcmp (*argv, "-f")))); })
== 0)
                                                                               
                                                                               
      ^      ~
minigzip.c:287:2080: warning: array index 3 is past the end of the array (which
contains 3 elements) [-Warray-bounds]
  ...- ((__const unsigned char *) (__const char *) ("-h"))[2]); if (__s2_len >
2 && __result == 0) __result = (__s1[3] - ((__const unsigned char *) (__const
char *) ("-h"))[3]); } } __result; }))) : __builtin_strcmp (*argv, "-h")))); })
== 0)
                                                                               
                                                                               
      ^      ~
minigzip.c:289:2080: warning: array index 3 is past the end of the array (which
contains 3 elements) [-Warray-bounds]
  ...- ((__const unsigned char *) (__const char *) ("-r"))[2]); if (__s2_len >
2 && __result == 0) __result = (__s1[3] - ((__const unsigned char *) (__const
char *) ("-r"))[3]); } } __result; }))) : __builtin_strcmp (*argv, "-r")))); })
== 0)
                                                                               
                                                                               
      ^      ~
4 warnings generated.
bluishred:~/work 758 ? clang -v
clang version 3.1 (trunk 147153)
Target: x86_64-unknown-linux-gnu
Thread model: posix

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