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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - InstCombine removes an icmp and select"
href="http://llvm.org/bugs/show_bug.cgi?id=21199">21199</a>
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<th>Summary</th>
<td>InstCombine removes an icmp and select
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>hans@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
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<p>
<div>
<pre>Consider the following IR:
; ModuleID = '<stdin>'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
declare void @f(i32)
define void @test(i32 %len) {
entry:
%cmp = icmp ult i32 %len, 8
%cond = select i1 %cmp, i32 %len, i32 8
%cmp11 = icmp ult i32 0, %cond
br i1 %cmp11, label %for.body, label %for.end
for.body: ; preds = %entry, %for.body
%i.02 = phi i32 [ %inc, %for.body ], [ 0, %entry ]
tail call void @f(i32 %cond)
%inc = add i32 %i.02, 1
%cmp1 = icmp ult i32 %inc, %cond
br i1 %cmp1, label %for.body, label %for.end
for.end: ; preds = %for.body, %entry
ret void
}
Passing it through instcombine like so:
$ bin/opt -instcombine < /tmp/c.ll -S -o -
Results in the first comparison and select going missing:
define void @test(i32 %len) {
entry:
%0 = icmp eq i32 %len, 0
br i1 %0, label %for.end, label %for.body
for.body: ; preds = %entry, %for.body
%i.02 = phi i32 [ %inc, %for.body ], [ 0, %entry ]
tail call void @f(i32 %len)
%inc = add i32 %i.02, 1
%cmp1 = icmp ult i32 %inc, %len
br i1 %cmp1, label %for.body, label %for.end</pre>
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