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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - pointer arithmetic with empty struct compiles into division by zero"
href="http://llvm.org/bugs/show_bug.cgi?id=15683">15683</a>
</td>
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<tr>
<th>Summary</th>
<td>pointer arithmetic with empty struct compiles into division by zero
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jari@kirma.fi
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Unoptimized compilation of following program emits code that includes division
by zero (apparently clang considers struct to be zero-sized, and doesn't handle
the special case?):
#include <stddef.h>
int main(int argc, char **argv)
{
struct {} x[2];
volatile ptrdiff_t y = 1+x-x;
return 0;
}
This issue occurs with -O0, but not with -O1.
Generated assembler below.
.file "struct_test.c"
.text
.globl main
.align 16, 0x90
.type main,@function
main: # @main
.cfi_startproc
# BB#0:
pushq %rbp
.Ltmp2:
.cfi_def_cfa_offset 16
.Ltmp3:
.cfi_offset %rbp, -16
movq %rsp, %rbp
.Ltmp4:
.cfi_def_cfa_register %rbp
movl $0, %eax
movl $0, -4(%rbp)
movl %edi, -8(%rbp)
movq %rsi, -16(%rbp)
xorl %esi, %esi
xorl %edx, %edx
movl %eax, -36(%rbp) # 4-byte Spill
movq %rsi, %rax
divq %rsi
movq %rax, -32(%rbp)
movl -36(%rbp), %eax # 4-byte Reload
popq %rbp
ret
.Ltmp5:
.size main, .Ltmp5-main
.cfi_endproc
.section ".note.GNU-stack","",@progbits</pre>
</div>
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