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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - InstCombine incorrectly rewrites indices of gep inbounds"
href="https://bugs.llvm.org/show_bug.cgi?id=44861">44861</a>
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<th>Summary</th>
<td>InstCombine incorrectly rewrites indices of gep inbounds
</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>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>juneyoung.lee@sf.snu.ac.kr
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
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<pre>```
$ cat input.ll
declare void @g(i8*)
define void @foo(i8* %ptr, i1 %cc1, i1 %cc2, i1 %cc3, i32 %arg) {
entry:
br i1 %cc1, label %do.end, label %if.then
if.then:
br i1 %cc2, label %do.body, label %do.end
do.body:
%phi = phi i32 [ %arg, %if.then ]
%phi.ext = zext i32 %phi to i64
%ptr2 = getelementptr inbounds i8, i8* %ptr, i64 %phi.ext
%ptr3 = getelementptr inbounds i8, i8* %ptr2, i64 -1
call void @g(i8* %ptr3)
br i1 %cc3, label %do.end, label %if.then
do.end:
ret void
}
$ opt -instcombine -S -o - input.ll
declare void @g(i8*)
define void @foo(i8* %ptr, i1 %cc1, i1 %cc2, i1 %cc3, i32 %arg) {
br i1 %cc1, label %do.end, label %if.then
if.then: ; preds = %do.body, %entry
br i1 %cc2, label %do.body, label %do.end
do.body: ; preds = %if.then
%phi.ext = zext i32 %arg to i64
%ptr2 = getelementptr inbounds i8, i8* %ptr, i64 -1
%ptr3 = getelementptr inbounds i8, i8* %ptr2, i64 %phi.ext
call void @g(i8* nonnull %ptr3)
br i1 %cc3, label %do.end, label %if.then
do.end: ; preds = %do.body, %if.then,
%entry
ret void
}
```
If %arg is 1, ptr3 in the source is `gep inb (gep inb ptr, 1), -1` whereas ptr3
in the target is `gep inb (gep inb ptr, -1), 1`.
This is incorrect because ptr3 in the tgt may be poison whereas ptr3 in the
source isn't.</pre>
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