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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 - __attribute__((pcs("aapcs-vfp"))) is not consistent"
href="https://bugs.llvm.org/show_bug.cgi?id=39982">39982</a>
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<th>Summary</th>
<td>__attribute__((pcs("aapcs-vfp"))) is not consistent
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</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>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: ARM
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>srhines@google.com
</td>
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<th>CC</th>
<td>kristof.beyls@arm.com, llvm-bugs@lists.llvm.org, peter.smith@linaro.org, Ties.Stuij@arm.com
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<p>
<div>
<pre>This is from an internal Google bug, but really has to do with ARM backend
handling of aapcs-vfp. From that bug:
float __attribute__((pcs("aapcs-vfp"))) baz(float x, float y) {
return y;
}
struct S {
float f;
float d;
};
float __attribute__((pcs("aapcs-vfp"))) foo(S s) {
return s.d;
}
float __attribute__((pcs("aapcs"))) bar(S s) {
return s.d;
}
Compilation in hard-fp mode produces expected output (
<a href="https://godbolt.org/z/SdXIsN">https://godbolt.org/z/SdXIsN</a> ):
baz(float, float):
vmov.f32 s0, s1
bx lr
foo(S):
vmov.f32 s0, s1
bx lr
bar(S):
mov r0, r1
bx lr
Compilation in soft-fp mode produces very strange output (
<a href="https://godbolt.org/z/HVVDtj">https://godbolt.org/z/HVVDtj</a> ):
baz(float, float):
vmov.f32 s0, s1
bx lr
foo(S):
vmov s0, r1
bx lr
bar(S):
mov r0, r1
bx lr
It looks as if "foo" function uses hard-fp mode for result but soft-fp for
input.
Unfortunatelly vulkan uses pcs("aapcs-vfp") thus we couldn't just ignore that
issue (even if it looks as if currently vulkan does not suffer from that issue
- there very few functions with float arguments and they all are compiled
identically in hardfp and pcs("aapcs-vfp") modes).</pre>
</div>
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