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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Opus miscompiled for ARM after ParallelDSP change r367389"
href="https://bugs.llvm.org/show_bug.cgi?id=43073">43073</a>
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<th>Summary</th>
<td>Opus miscompiled for ARM after ParallelDSP change r367389
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hans@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, sam.parker@arm.com
</td>
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<pre>Some WebRTC tests which use Opus started failing on Android after LLVM r367389
(<a href="https://bugs.chromium.org/p/webrtc/issues/detail?id=10887">https://bugs.chromium.org/p/webrtc/issues/detail?id=10887</a>)
It's very possible that the change itself is fine, but that it exposed
ParallelDSP to more code that then got miscompiled due to some already existing
bug in the pass.
Here's a reduced repro which I think shows the problem:
b.c:
typedef short int16_t;
typedef unsigned short uint16_t;
typedef int int32_t;
typedef unsigned int uint32_t;
#define MLA(a, m, n) (int32_t)((uint32_t)(a) + (uint32_t)((int32_t)(int16_t)(m)
* (int32_t)(int16_t)(n)))
int32_t bar(int32_t a, int32_t b);
int32_t foo(const int16_t *in, const int16_t *b)
{
uint32_t x;
x = bar(in[0], b[0]);
x = MLA(x, in[-1], b[1]);
x = MLA(x, in[-2], b[2]);
x = MLA(x, in[-3], b[3]);
x = MLA(x, in[-4], b[4]);
x = MLA(x, in[-5], b[5]);
return x;
}
$ clang --target=arm-linux-androideabi -march=armv7-a -mthumb
-fomit-frame-pointer -O3 -S /tmp/b.c -o -
[...]
foo:
.fnstart
@ %bb.0: @ %entry
.save {r4, r5, r7, lr}
push {r4, r5, r7, lr}
mov r4, r1
mov r5, r0
ldrsh.w r1, [r1]
ldrsh.w r0, [r0]
bl bar
ldr r2, [r5, #-4]
ldr.w r3, [r4, #2]
ldr r1, [r5, #-8]
ldr.w r5, [r4, #6]
smlabt r0, r3, r2, r0
smladx r0, r3, r2, r0
smladx r0, r5, r1, r0
pop {r4, r5, r7, pc}
.Lfunc_end0:
.size foo, .Lfunc_end0-foo
.cantunwind
.fnend
My ARM/Thumb is rusty, but it appears that both the SMLABT and the first SMLADX
instruction are accumulating in[-1] * b[1] into r0, and that in[-5] and b[5]
are never even loaded.</pre>
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