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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ThinLTO does not drop aliases to dead targets."
href="https://bugs.llvm.org/show_bug.cgi?id=36208">36208</a>
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<th>Summary</th>
<td>ThinLTO does not drop aliases to dead targets.
</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>Windows NT
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Linker
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>grimar@accesssoftek.com
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
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<pre>Currently ThinLTO backend does not support dropping aliases to dead functions.
(see comment at
<a href="https://github.com/llvm-mirror/llvm/blob/master/lib/LTO/LTOBackend.cpp#L411">https://github.com/llvm-mirror/llvm/blob/master/lib/LTO/LTOBackend.cpp#L411</a>)
For example if we have following testcase where foo is prevailing and bar is
not prevailing:
; RUN: opt -module-summary %s -o %t1.bc
; RUN: llvm-lto2 run %t1.bc -r %t1.bc,fooAlias,pl -r %t1.bc,barAlias,pl \
; RUN: -r %t1.bc,foo,plx -r %t1.bc,bar,lx \
; RUN: -o %t2.o -save-temps
; RUN: llvm-dis -o %t.dis %t2.o.1.2.internalize.bc
; RUN: opt -module-summary %t.dis -o %t2.bc
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@fooAlias = alias i32(), i32()* @foo
define i32 @foo() {
ret i32 11
}
@barAlias = alias i32(), i32()* @bar
define i32 @bar() {
ret i32 22
}
It will fail with:
"Alias must point to a definition i32 ()* @barAlias"
because LTO drops bar, but does not drop it's alias.
Disasm of %t2.o.1.2.internalize.bc (%t.dis content):
@fooAlias = internal alias i32 (), i32 ()* @foo
@barAlias = internal alias i32 (), i32 ()* @bar
define dso_local i32 @foo() {
ret i32 11
}
declare dso_local i32 @bar()
Expected result is that barAlias should be eliminated I think.</pre>
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