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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ARM backend: Wrong tailcalls if varargs function"
href="https://bugs.llvm.org/show_bug.cgi?id=45234">45234</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>ARM backend: Wrong tailcalls if varargs function
</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>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>manjian2006@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>```c++
extern int GetPrimitiveType(int o);
extern double DoubleMethod(int o, ...);
namespace {
double __attribute__((noinline)) Load(int i) {
double d = DoubleMethod(1, i);
return d;
}
}
double ParseObject(int o) {
switch(GetPrimitiveType(o)) {
case 1:
return Load(o);
default:
return 1.0;
}
}
```
```asm
_Z11ParseObjecti:
.fnstart
@ %bb.0:
.save {r4, lr}
push {r4, lr}
mov r4, r0
bl _Z16GetPrimitiveTypei
cmp r0, #1
bne .LBB0_2
@ %bb.1:
mov r0, r4
bl _ZN12_GLOBAL__N_14LoadEi
vmov r0, r1, d0
pop {r4, pc}
.LBB0_2:
vmov.f64 d0, #1.000000e+00
vmov r0, r1, d0
pop {r4, pc}
```
The caller thinks the return location is d0.
```c++
_ZN12_GLOBAL__N_14LoadEi:
.fnstart
@ %bb.0:
mov r1, r0
movs r0, #1
b _Z12DoubleMethodiz
```
The tail call to _Z12DoubleMethodiz regardless the calee's cc, which is
probably AAPCS. The AAPCS's return location for the type double is in r0, r1.
The bug point is at the function
ARMTargetLowering::IsEligibleForTailCallOptimization in the file
lib/Target/ARM/ARMISelLowering.cpp.
```c++
if (!CCState::resultsCompatible(CalleeCC, CallerCC, MF, C, Ins,
CCAssignFnForReturn(CalleeCC, isVarArg),
CCAssignFnForReturn(CallerCC, isVarArg)))
return false;
```
Should be:
```c++
if (!CCState::resultsCompatible(
CalleeCC, CallerCC, MF, C, Ins,
CCAssignFnForReturn(CalleeCC, isVarArg),
CCAssignFnForReturn(CallerCC, CallerF.isVarArg())))
return false;
```</pre>
</div>
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