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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Unnecessary narrowing of register reference in DW_AT_location for int parameter"
href="http://bugs.llvm.org/show_bug.cgi?id=32288">32288</a>
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<th>Summary</th>
<td>Unnecessary narrowing of register reference in DW_AT_location for int parameter
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>DebugInfo
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>dblaikie@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=18099" name="attach_18099" title="repro IR">attachment 18099</a> <a href="attachment.cgi?id=18099&action=edit" title="repro IR">[details]</a></span>
repro IR
Given:
void f(int i) { }
(which produces the attached LLVM IR)
The DWARF generated by LLVM includes this location:
0x55 0x93 0x04
DW_OP_reg5 DW_OP_piece(4)
When GCC's DWARF is simply 0x55 (DW_OP_reg5) without the DW_OP_piece. I believe
it's reasonable to assume the DWARF consumer knows which part of a register
logically holds the value (low bytes, high bytes, how many bytes, etc) for a
primitive value like an integer.
If something fancy is going on, like the register only contains part of an
object (eg: struct foo { int x, y, z; }; gets {reg5, piece(8), reg4, piece(4)}
which is probably important ({reg5, reg4} seems inadequate) - interestingly,
GCC uses fbreg (insufficient optimization?) even at -O3)
PR33269 has some related work.
This could be changed in DwarfExpression::setSubRegisterPiece could be a no-op
when the offset is zero? (But this wouldn't be quite right for a case where
that piece was used as part of a larger value, perhaps... as in the 'foo'
example above)</pre>
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