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<body><span class="vcard"><a class="email" href="mailto:t.scheller@samsung.com" title="Tilmann Scheller <t.scheller@samsung.com>"> <span class="fn">Tilmann Scheller</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED WORKSFORME - select in thumb2 sign extends constants when it shouldn't"
href="http://llvm.org/bugs/show_bug.cgi?id=19107">bug 19107</a>
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<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
</tr>
<tr>
<td style="text-align:right;">CC</td>
<td>
</td>
<td>t.scheller@samsung.com
</td>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>WORKSFORME
</td>
</tr></table>
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED WORKSFORME - select in thumb2 sign extends constants when it shouldn't"
href="http://llvm.org/bugs/show_bug.cgi?id=19107#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED WORKSFORME - select in thumb2 sign extends constants when it shouldn't"
href="http://llvm.org/bugs/show_bug.cgi?id=19107">bug 19107</a>
from <span class="vcard"><a class="email" href="mailto:t.scheller@samsung.com" title="Tilmann Scheller <t.scheller@samsung.com>"> <span class="fn">Tilmann Scheller</span></a>
</span></b>
<pre>Just tried this with trunk, getting the following machine code for the bad2
function:
bad2:
.fnstart
.Leh_func_begin1:
@ BB#0:
uxtb r1, r1
uxtb r2, r0
cmp r2, r1
it hi
mvnhi r0, #127
bx lr
So indeed the 128 constant is sign extended, however this still matches the
semantics of the LLVM IR, so I don't think we have an actual bug here.
Since there are no 8-bit registers, i8 values effectively get promoted to i32.
In other words, the upper 24-bits of a promoted i8 value are undefined. That's
also why we need the two uxtb instructions in the beginning, since we need to
assume that the upper 24-bits of the incoming values are garbage.</pre>
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