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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Inefficient 64-bit absolute addresses in Cygwin"
href="https://bugs.llvm.org/show_bug.cgi?id=42983">42983</a>
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<th>Summary</th>
<td>Inefficient 64-bit absolute addresses in Cygwin
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>5.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</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
</td>
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<th>Component</th>
<td>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>agner@agner.org
</td>
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Cygwin Clang v. 5.0.1 is using 64-bit absolute addresses when accessing static
data in 64-bit mode. This is inefficient because it requires an extra 10-bytes
long instruction for loading an address into a register every time it needs to
access static data.
Linux Clang v. 6.0.0 with --target=x86_64-win64-windows gives the more
efficient relative addresses, as do all other compilers.
Is this a Cygwin-only issue? I posted it to the cygwin mailing list, but they
advised me to go here.
Test case:
#include <immintrin.h>
__m128d test (__m128d a) {
__m128d b = _mm_add_pd(a, _mm_set1_pd(1.5));
__m128d c = _mm_mul_pd(b, _mm_set1_pd(2.5));
return c;
}
Cygwin Clang assembly output:
_Z4testDv2_d:
vmovapd (%rcx), %xmm0
movabsq $.LCPI0_0, %rax
vaddpd (%rax), %xmm0, %xmm0
movabsq $.LCPI0_1, %rax
vmulpd (%rax), %xmm0, %xmm0
retq
Linux Clang assembly output with windows target:
"?test@@YAU__m128d@@U1@@Z": # @"\01?test@@YAU__m128d@@U1@@Z"
# %bb.0:
vmovapd (%rcx), %xmm0
vaddpd __xmm@3ff80000000000003ff8000000000000(%rip), %xmm0, %xmm0
vmulpd __xmm@40040000000000004004000000000000(%rip), %xmm0, %xmm0
retq</pre>
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