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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 - [MachineCopyPropagagation] Incorrect dead flag survives"
href="https://bugs.llvm.org/show_bug.cgi?id=33037">33037</a>
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<th>Summary</th>
<td>[MachineCopyPropagagation] Incorrect dead flag survives
</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>
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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>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>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>paulsson@linux.vnet.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
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<pre>Created <span class=""><a href="attachment.cgi?id=18438" name="attach_18438" title="reduced testcase">attachment 18438</a> <a href="attachment.cgi?id=18438&action=edit" title="reduced testcase">[details]</a></span>
reduced testcase
In this MBB:
BB#0: derived from LLVM BB %BB
%V0<def> = VGBM 0
%V1<def,dead> = COPY %V0
%V1<def> = COPY %V0
%V1<def,tied1> = VLEIH %V1<kill,tied0>, 0, 1
%V0<def> = VCEQH %V1<kill>, %V0<kill>
%R1D<def> = LARL <cp#0>
%V1<def> = VL %R1D<kill>, 0, %noreg; mem:LD16[ConstantPool](align=8)
%V0<def,dead> = VPERM %V0<kill>, %V0<undef>, %V1<kill>
, the first COPY of %V0 to %V1 has a dead flag, while the second one doesn't.
The optimization seems to think the second COPY is redundant, and calls
eraseIfRedundant(). Afterwards, this results in:
%V1<def,dead> = COPY %V0
%V1<def,tied1> = VLEIH %V1<kill,tied0>, 0, 1
*** Bad machine code: Using an undefined physical register ***
- function: autogen_SD11756
- basic block: BB#0 BB (0x3c90be8)
- instruction: %V1<def,tied1> = VLEIH
- operand 1: %V1<kill,tied0>
Somehow, the dead flag should have been removed.
Run line: llc -O3 -mtriple=s390x-linux-gnu -mcpu=z13 -verify-machineinstrs
-disable-cgp -pre-RA-sched=source -disable-machine-dce
-join-liveintervals=false -o /dev/null ./tc_mcp_undefphysreg.ll</pre>
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