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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed store-load forwarding due to asymmetric alias information"
href="https://bugs.llvm.org/show_bug.cgi?id=39186">39186</a>
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<th>Summary</th>
<td>Missed store-load forwarding due to asymmetric alias information
</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
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>jeroen.dobbelaere@synopsys.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<pre>Created <span class=""><a href="attachment.cgi?id=20966" name="attach_20966" title="test.c showing two similar cases, one that gets optimized, one that doesn't">attachment 20966</a> <a href="attachment.cgi?id=20966&action=edit" title="test.c showing two similar cases, one that gets optimized, one that doesn't">[details]</a></span>
test.c showing two similar cases, one that gets optimized, one that doesn't
The attached testcase results in following asymmetric alias relationship
between two stores and one load.
(A) store 42, %0
(B) store 43, %1
(C) load %0
for FOO:
(A)-(B): may alias
(A)-(C): must alias
(B)-(C): no alias (due to __restrict)
for BAR:
(A)-(B): no alias (due to __restrict)
(A)-(C): must alias
(B)-(C): may alias
Content after inlining:
case 'FOO':
*** IR Dump After Function Integration/Inlining ***
; Function Attrs: nounwind uwtable
define dso_local i32 @foo(i32*, i32*) local_unnamed_addr #0 {
store i32 42, i32* %0, align 4, !tbaa !2
store i32 43, i32* %1, align 4, !tbaa !2, !noalias !6
%3 = load i32, i32* %0, align 4, !tbaa !2, !alias.scope !6
ret i32 %3
}
case 'BAR':
*** IR Dump After Function Integration/Inlining ***
; Function Attrs: nounwind uwtable
define dso_local i32 @bar(i32*, i32*) local_unnamed_addr #2 {
store i32 42, i32* %0, align 4, !tbaa !2, !alias.scope !6
store i32 43, i32* %1, align 4, !tbaa !2, !noalias !6
%3 = load i32, i32* %0, align 4, !tbaa !2
ret i32 %3
}
- EarlyCSE is able to optimize foo and see that the load is not necessary.
- EarlyCSE, GVN and NewGVN are not able to optimize bar.
NOTE: gcc is able to optimize both cases</pre>
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