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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Inefficient codegen for postincrement of _ExtInt(256)"
href="https://bugs.llvm.org/show_bug.cgi?id=45650">45650</a>
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<th>Summary</th>
<td>Inefficient codegen for postincrement of _ExtInt(256)
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
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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>-New Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>arthur.j.odwyer@gmail.com
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<pre>The following source code:
// <a href="https://wide.godbolt.org/z/t6j6Z">https://wide.godbolt.org/z/t6j6Z</a>-
using uint256 = unsigned _ExtInt(256);
extern auto inc2(uint256& a)
{
return a++;
}
produces the following x86-64 assembly at -O3:
inc2(unsigned int _ExtInt<256>&): # @inc2(unsigned int _ExtInt<256>&)
pushq %rbx
movq %rdi, %rax
movq 24(%rsi), %r8
movq 16(%rsi), %r11
movq (%rsi), %r9
movq 8(%rsi), %r10
movq %r9, %rdi
addq $1, %rdi
movq %r10, %rcx
adcq $0, %rcx
movq %r11, %rdx
adcq $0, %rdx
movq %r8, %rbx
adcq $0, %rbx
movq %rdi, (%rsi)
movq %rcx, 8(%rsi)
movq %rdx, 16(%rsi)
movq %rbx, 24(%rsi)
movq %r11, 16(%rax)
movq %r8, 24(%rax)
movq %r9, (%rax)
movq %r10, 8(%rax)
popq %rbx
retq
Also, completely tangential, I notice that the demangler thinks the spelling is
`ExtInt<256>`, but the real syntax is supposed to be `_ExtInt(256)`.</pre>
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