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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [DebugInfo@O2] DAGCombine drops easily salvageable variable location"
href="https://bugs.llvm.org/show_bug.cgi?id=44881">44881</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[DebugInfo@O2] DAGCombine drops easily salvageable variable location
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</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>Keywords</th>
<td>wrong-debug
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jeremy.morse.llvm@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>chackz0x12@gmail.com, greg.bedwell@sony.com, llvm-bugs@lists.llvm.org, orlando.hyams@sony.com, paul.robinson@am.sony.com, stephen.tozer@sony.com, vsk@apple.com
</td>
</tr>
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<th>Blocks</th>
<td>38768
</td>
</tr></table>
<p>
<div>
<pre>Spun off from <a class="bz_bug_link
bz_status_NEW "
title="NEW - [DebugInfo] Arguments are lost after a call across TUs"
href="show_bug.cgi?id=39724">bug 39724</a>, Davides test case which I copy below has 'l' optimised
out in the fn1 function. The cause appears to be a DAGCombine that drops the
multiply, which the SelectionDAG salvager can't recover. This is true of todays
master, 2733ad2c24 ish.
--------8<--------
a.c:
extern void other_func(long int, long int, long int);
__attribute__((noinline))
int fn1 (long int x, long int y, long int z) {
int l = x * 2;
int q = y * z;
other_func(x, y, z);
return l + q;
}
__attribute__((noinline)) long int
fn2 (long int a, long int b, long int c)
{
long int q = 2 * a;
return fn1 (5, 6, 7);
}
int main(void) {
return fn2(14, 23, 34);
}
b.c:
void other_func(long int a, long int b, long int c) {}
built with: ${CC} a.c b.c -O3 -g
-------->8--------
I guess this ticket can more broadly represents the fact that all the folding /
morphing in DAGCombine isn't robustly salvaged.</pre>
</div>
</p>
<div id="referenced">
<hr style="border: 1px dashed #969696">
<b>Referenced Bugs:</b>
<ul>
<li>
[<a class="bz_bug_link
bz_status_NEW "
title="NEW - [meta][DebugInfo] Umbrella bug for poor debug experiences"
href="https://bugs.llvm.org/show_bug.cgi?id=38768">Bug 38768</a>] [meta][DebugInfo] Umbrella bug for poor debug experiences
</li>
</ul>
</div>
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