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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [ARMv6M] missing tail call opportunities and unneeded instr emitted"
href="https://llvm.org/bugs/show_bug.cgi?id=31227">31227</a>
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<th>Summary</th>
<td>[ARMv6M] missing tail call opportunities and unneeded instr emitted
</td>
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<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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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>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</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>weimingz@codeaurora.org
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>test.c:
__attribute__((noinline)) static int foo(int a) {
return a*10;
}
int caller(int b) {
b += 10;
return foo(b);
}
clang -mcpu=cortex-m0 -target armv6m-linux-gnueabi -S -Os test.c -o test.llvm.s
test.llvm.s:
caller:
.fnstart
push {r7, lr}
add r7, sp, #0 ==> why do we need this?
adds r0, #10
bl foo
pop {r7, pc}
Other compilers generate:
00000006 <caller>:
6: 300a adds r0, #10
8: e7fe b.n 0 <foo>
LLVM generated code has 2 problems:
1. unneeded instruction "add r7, sp, #0" is emitted
2. Other compiler can do tail call. on armv6m, "b" can be thumb2 with imm11 but
still not a big range. Maybe linker can do trampoline?</pre>
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