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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Loop Unswitch creates duplicated dbg.declare"
href="https://bugs.llvm.org/show_bug.cgi?id=33355">33355</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Loop Unswitch creates duplicated dbg.declare
</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>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>mattias.v.eriksson@ericsson.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=18591" name="attach_18591" title="Reproducer for duplicated dbg.declare">attachment 18591</a> <a href="attachment.cgi?id=18591&action=edit" title="Reproducer for duplicated dbg.declare">[details]</a></span>
Reproducer for duplicated dbg.declare
The function f2 has a byval argument that is dead ("dum"). f2 is
inlined into f3 and the dbg.declare is inlined to reflect
that "dum" is "p1" in the inlined code.
Input to 'Function Integration/Inlining':
; Function Attrs: nounwind readonly
define i16 @f2(%struct.S* byval nocapture readnone align 1 %dum)
local_unnamed_addr #0 !dbg !11 {
entry:
call void @llvm.dbg.declare(metadata %struct.S* %dum, metadata !18, metadata
!19), !dbg !20
%0 = load i16, i16* @a, align 1, !dbg !21, !tbaa !22
ret i16 %0, !dbg !26
}
define void @f3(%struct.S* byval align 1 %p1) local_unnamed_addr #2 !dbg !27 {
entry:
call void @llvm.dbg.declare(metadata %struct.S* %p1, metadata !31, metadata
!19), !dbg !32
br label %lbl1, !dbg !33
lbl1: ; preds = %lbl1, %entry
%call = call i16 @f2(%struct.S* byval nonnull align 1 %p1), !dbg !34
After 'Function Integration/Inlining':
; Function Attrs: nounwind
define void @f3(%struct.S* byval align 1 %p1) local_unnamed_addr #2 !dbg !27 {
entry:
call void @llvm.dbg.declare(metadata %struct.S* %p1, metadata !31, metadata
!19), !dbg !32
br label %lbl1, !dbg !33
lbl1: ; preds = %lbl1, %entry
call void @llvm.dbg.declare(metadata %struct.S* %p1, metadata !18, metadata
!19), !dbg !34
%0 = load i16, i16* @a, align 1, !dbg !36, !tbaa !22
call void @f1(i16 %0), !dbg !37
Some relevant metadata:
!18 = !DILocalVariable(name: "dum", arg: 1, scope: !11, file: !3, line: 8,
type: !14)
!19 = !DIExpression()
!31 = !DILocalVariable(name: "p1", arg: 1, scope: !27, file: !3, line: 15,
type: !14)
A while later, 'Unswitch loops' duplicates dum's dbg.declare:
define void @f3(%struct.S* byval nocapture readonly align 1 %p1)
local_unnamed_addr #2 !dbg !27 {
...
lbl1.us: ; preds = %lbl1.us,
%entry.split.us
call void @llvm.dbg.declare(metadata %struct.S* %p1, metadata !18, metadata
!19), !dbg !34
%1 = load i16, i16* @a, align 1, !dbg !36, !tbaa !22
call void @f1(i16 %1), !dbg !37
...
lbl1: ; preds = %lbl1, %entry.split
call void @llvm.dbg.declare(metadata %struct.S* %p1, metadata !18, metadata
!19), !dbg !34
%2 = load i16, i16* @a, align 1, !dbg !36, !tbaa !22
call void @f1(i16 %2), !dbg !37
And then in the late stages of llc I get a crash in DwarfDebug
because it expects that there can't be duplicate dbg.declares.
(Same assertion as in <a class="bz_bug_link
bz_status_NEW "
title="NEW - Assertion failed: ("conflicting locations for variable")"
href="show_bug.cgi?id=33157">bug 33157</a>.)
I am a bit confused about how dbg.declare is supposed to work in
this case. The documentation says: "This intrinsic provides
information about a local element (e.g., variable). The first
argument is metadata holding the alloca for the variable." But
there is no alloca associated with %p1 here. Is this an omission
in the documentation?
Are duplicated dbg.declares allowed? Then the bug is in
DwarfDebug for crashing, not in loop unswitch.
Reproduce like this:
opt -S -inline -functionattrs -licm -loop-unswitch -o - inline.ll | grep
dbg.declare | sort | uniq -c
1 call void @llvm.dbg.declare(metadata %struct.S* %dum, metadata !18,
metadata !19), !dbg !20
2 call void @llvm.dbg.declare(metadata %struct.S* %p1, metadata !18,
metadata !19), !dbg !34
1 call void @llvm.dbg.declare(metadata %struct.S* %p1, metadata !31,
metadata !19), !dbg !32
1 declare void @llvm.dbg.declare(metadata, metadata, metadata) #1</pre>
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