[LLVMbugs] [Bug 15048] New: bad code for struct initialization on x86

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=15048

             Bug #: 15048
           Summary: bad code for struct initialization on x86
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: dhazeghi at yahoo.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


We've found the following snippet (derived from 931004-11.c in the gcc
testsuite) which produces incorrect results with clang 3.2 and trunk when
compiled for x86_64-linux in 32-bit mode, using -O3.  At lower optimization
levels, the output is correct.  This may be connected to bug #14972, although
it triggers only at -O3, unlike that bug.


$ cat reduced.c
#include <stdio.h>

struct tiny {
  unsigned char c;
  unsigned char d;
  unsigned char e;
};

void foo (struct tiny x, struct tiny y, struct tiny z) {
  if (x.c != 1)
    printf("BUG1\n");

  if (x.e != 1)
    printf("BUG2\n");

  if (y.c != 1)
    printf("BUG3\n");

  if (y.d != 1)
    printf("BUG4\n");

  if (z.c != 1)
    printf("BUG5\n");
}

int main (void) {

  struct tiny x[3];

  x[0].c = 1;
  x[1].c = 1;
  x[2].c = 1;
  x[0].d = 1;
  x[1].d = 1;
  x[2].d = 1;
  x[0].e = 1;
  x[1].e = 1;
  x[2].e = 1;

  foo (x[0], x[1], x[2]); 

  printf("END\n");

  return 0;
}

$ clang -O2 -m32 reduced.c
$ ./a.out 
END
$ clang -O3 -m32 reduced.c
$ ./a.out 
BUG1
BUG2
END

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