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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Simpler DWARF for C99 VLAs"
href="https://bugs.llvm.org/show_bug.cgi?id=36322">36322</a>
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<th>Summary</th>
<td>Simpler DWARF for C99 VLAs
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>paul_robinson@playstation.sony.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
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<pre>Filed on behalf of Carlos Enciso, who made this post-commit suggestion
on Phabricator D41698:
Hi @sdesmalen!
For the following test case
int main() {
int size = 2;
int var[size];
var[1] = 1;
return 0;
}
I compared the DWARF generated by GCC and it looks like
DW_TAG_variable "var"
DW_AT_location ...
DW_AT_type DW_FORM_ref4
DW_TAG_array_type
DW_AT_type -> "int"
DW_TAG_subrange_type
DW_AT_type -> "sizetype"
DW_AT_upper_bound DW_FORM_exprloc [4] = { DW_OP_fbreg 0xffffffb8
DW_OP_deref }
GCC use DW_AT_upper_bound with an associated location expression to describe
the VLA boundaries.
In order to reduce the side effects created by the artifical-variable as
described in my previous comment
(<a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED - Debug info generated for arrays is not what GDB expects (not as good as GCC's)"
href="show_bug.cgi?id=30553#c3">https://bugs.llvm.org/show_bug.cgi?id=30553#c3</a>) and to keep the generated
DWARF within a reasonable size, I would suggest the GCC aproach as a size
optimization.
The DWARF description of the artificial-variable could be removed and its
location expression used by the array's subrange_type, instead of the
subrange_type making a reference to the artificial-variable.</pre>
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