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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missing identical block merging"
href="https://bugs.llvm.org/show_bug.cgi?id=33583">33583</a>
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<th>Summary</th>
<td>Missing identical block merging
</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>All
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<th>Status</th>
<td>NEW
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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>davide@freebsd.org
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<th>CC</th>
<td>filcab@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, simon.f.whittaker@gmail.com
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<pre>LLVM lowers the following (with -O3 -fno-vectorize -c)
extern void f4();
void function(int x) {
if (x == 0) f4();
else if (x == 1) f4();
else if (x == 2) f4();
else if (x == 3) f4();
else if (x == 4) f4();
else if (x == 5) f4();
else if (x == 6) f4();
}
into a switch, but duplicates the destination block n times,
i.e.
switch i32 %0, label %9 [
i32 0, label %2
i32 1, label %3
i32 2, label %4
i32 3, label %5
i32 4, label %6
i32 5, label %7
i32 6, label %8
]
; <label>:2: ; preds = %1
tail call void @f4()()
br label %9
; <label>:3: ; preds = %1
tail call void @f4()()
br label %9
; <label>:4: ; preds = %1
tail call void @f4()()
br label %9
; <label>:5: ; preds = %1
tail call void @f4()()
br label %9
; <label>:6: ; preds = %1
tail call void @f4()()
br label %9
; <label>:7: ; preds = %1
tail call void @f4()()
br label %9
We manage to recognize identical blocks in the backend and merge them,
but it seems we could do it already in the middle-end.</pre>
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