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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Consider lowering the i686-windows DataLayout alignment of i64 to 32 bits"
href="https://bugs.llvm.org/show_bug.cgi?id=35215">35215</a>
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<th>Summary</th>
<td>Consider lowering the i686-windows DataLayout alignment of i64 to 32 bits
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<th>Product</th>
<td>libraries
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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>Windows NT
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<th>Status</th>
<td>NEW
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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: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>rnk@google.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>This is my current triple and datalayout for x86 Windows:
target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
target triple = "i386-pc-windows-msvc19.11.25508"
We should reconsider the i64:64 part and consider adding f64:32:64.
My argument for doing this is that "ABI" alignment in LLVM is a little too
overloaded. It is used for the alignment used in LLVM struct layout in addition
to some other things like va_arg lowering.
The reality is that i64 arguments and stack allocations are generally not
aligned, and you can't assume that any unadorned i64 load is really 8 byte
aligned. However, in structs, 64-bit integers and doubles are naturally
aligned. Since struct layout is mainly a frontend responsibility at this point,
we should be able to lower LLVM's alignment without affecting clang.
This is similar to how we implemented -malign-double in clang without changing
LLVM.</pre>
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