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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Passing values to inline assembly via high-byte registers can cause unencodable instructions"
href="https://bugs.llvm.org/show_bug.cgi?id=45865">45865</a>
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<th>Summary</th>
<td>Passing values to inline assembly via high-byte registers can cause unencodable instructions
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>10.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>josephcsible@gmail.com
</td>
</tr>
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=23467" name="attach_23467" title="Result of clang -O -emit-llvm -c -o foo.bc foo.c && bugpoint -llc-safe foo.bc">attachment 23467</a> <a href="attachment.cgi?id=23467&action=edit" title="Result of clang -O -emit-llvm -c -o foo.bc foo.c && bugpoint -llc-safe foo.bc">[details]</a></span>
Result of clang -O -emit-llvm -c -o foo.bc foo.c && bugpoint -llc-safe foo.bc
Consider this minimal C function:
void f(char x) {
register char y asm("ah") = x;
asm volatile("" :: "r"(y));
}
When I compile it with any optimization level except -O0, the code generator
fails with "Cannot encode high byte register in REX-prefixed instruction".</pre>
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