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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - llvm.bitreverse.i64 returns wrong value"
href="https://bugs.llvm.org/show_bug.cgi?id=36253">36253</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>llvm.bitreverse.i64 returns wrong value
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>5.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: PowerPC
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kai@redstar.de
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=19818" name="attach_19818" title="LLVM IR demonstring the problem.">attachment 19818</a> <a href="attachment.cgi?id=19818&action=edit" title="LLVM IR demonstring the problem.">[details]</a></span>
LLVM IR demonstring the problem.
The following code produces an unexpected output. It is a reduced version of
the following D code:
import ldc.intrinsics;
import core.stdc.stdio : printf;
int main()
{
auto exp = 1UL << 63;
printf("%lx\n", exp);
auto arg = 1UL << 0;
printf("%lx\n", arg);
auto val = llvm_bitreverse(arg);
printf("%lx\n", val);
return exp != val;
}
LLVM IR:
source_filename = "bitop.d"
target datalayout = "e-m:e-i64:64-n32:64"
target triple = "powerpc64le-unknown-linux-gnu"
@.str = private unnamed_addr constant [5 x i8] c"%lx\0A\00"
declare signext i32 @printf(i8*, ...)
declare i64 @llvm.bitreverse.i64(i64)
define signext i32 @main(i32 signext %argc_arg, i8** %argv_arg) {
%exp = alloca i64, align 8
%arg = alloca i64, align 8
%val = alloca i64, align 8
store i64 -9223372036854775808, i64* %exp
%1 = load i64, i64* %exp
%2 = call signext i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x
i8], [5 x i8]* @.str, i32 0, i32 0), i64 %1)
store i64 1, i64* %arg
%3 = load i64, i64* %arg
%4 = call signext i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x
i8], [5 x i8]* @.str, i32 0, i32 0), i64 %3)
%5 = load i64, i64* %arg
%6 = call i64 @llvm.bitreverse.i64(i64 %5)
store i64 %6, i64* %val
%7 = load i64, i64* %val
%8 = call signext i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x
i8], [5 x i8]* @.str, i32 0, i32 0), i64 %7)
%9 = load i64, i64* %exp
%10 = load i64, i64* %val
%11 = icmp ne i64 %9, %10
%12 = zext i1 %11 to i32
ret i32 %12
}
Compile and run:
llc -filetype=obj bitop.ll
gcc bitop.o -o bitop
./bitop
echo "Ret: $?"
Result:
8000000000000000
1
80000000
Ret: 1
If you change the line
%6 = call i64 @llvm.bitreverse.i64(i64 %5)
to
%6 = call i64 @llvm.bitreverse.i64(i64 %3)
or to
%6 = call i64 @llvm.bitreverse.i64(i64 1)
then the expected output
8000000000000000
1
8000000000000000
Ret: 0
is produced.
LLVM used:
ubuntu@ldc:/tmp/unittest$ /home/ubuntu/build-llvm/bin/llc --version
LLVM (<a href="http://llvm.org/">http://llvm.org/</a>):
LLVM version 5.0.1git-6af15925d78
DEBUG build with assertions.
Default target: powerpc64le-unknown-linux-gnu
Host CPU: pwr8
Registered Targets:
nvptx - NVIDIA PTX 32-bit
nvptx64 - NVIDIA PTX 64-bit
ppc32 - PowerPC 32
ppc64 - PowerPC 64
ppc64le - PowerPC 64 LE
Environment:
ubuntu@ldc:/tmp/unittest$ uname -a
Linux ldc 4.13.0-32-generic #35-Ubuntu SMP Thu Jan 25 09:05:20 UTC 2018 ppc64le
ppc64le ppc64le GNU/Linux</pre>
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