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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 - LoopVectorizer calls getCastInstrCost for an illegal trunc instruction"
href="https://bugs.llvm.org/show_bug.cgi?id=36433">36433</a>
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<tr>
<th>Summary</th>
<td>LoopVectorizer calls getCastInstrCost for an illegal trunc instruction
</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>
</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>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<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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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=19895" name="attach_19895" title="reduced testcase">attachment 19895</a> <a href="attachment.cgi?id=19895&action=edit" title="reduced testcase">[details]</a></span>
reduced testcase
getInstructionCost():
(gdb) p I->dump()
%17 = trunc i32 %16 to i16
(gdb) p SrcVecTy->dump()
<2 x i32>
(gdb) p RetTy->dump()
i8
(gdb) p VectorTy->dump()
<2 x i8>
canTruncateToMinimalBitwidth(I, VF) returns true
(gdb) p SrcVecTy->dump()
<2 x i8>
(gdb) p VectorTy->dump()
<2 x i16>
TargetTransformInfo::getCastInstrCost() :
(gdb) p Dst->dump()
<2 x i16>
(gdb) p Src->dump()
<2 x i8>
These types do not make sense for a truncate.
->
lib/Target/SystemZ/SystemZTargetTransformInfo.cpp:520: unsigned int
llvm::SystemZTTIImpl::getVectorTruncCost(llvm::Type*, llvm::Type*): Assertion
`SrcTy->getPrimitiveSizeInBits() > DstTy->getPrimitiveSizeInBits() && "Packing
must reduce size of vector type."' failed.
I would hope that the SystemZ assert is correct, and that the loop vectorizer
should not have made this call.
---
Please excuse my simple patch for disabling instruction combining, which is how
this test case appeared with csmith.
I first tried to reproduce this with opt -debug-pass=Arguments and then using
opt with all the explicit passes without -O3, but that did not work for some
reason. First I got
'LLVM ERROR: Trying to construct TargetPassConfig without a target machine.
Scheduling a CodeGen pass without a target triple set?'
This is weird, because I passed the triple, and it's also in the input file.
When I removed the -targetpassconfig argument, I didn't get the error.
Also did not know how to do something like -stop-before=loop-vectorize.
So, to rerun (with the patch for -disable-instcombine applied):
bin/opt -O3 -mcpu=z13 -o out.opt.ll tc_loopvec_trunc.ll
-enable-loop-versioning-licm -disable-instcombine -enable-tbaa=false
BTW, I see a *lot* of errors when I use my disable-instcombine option. Given
this, I feel like I must ask if instcombine is truly optional, or if other
passes depend on it? Before rewriting instcombine per some discussion I read a
while back ago, I hope people are aware of this...</pre>
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