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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 - [X86] Failure to move indvar constant offset into final address gen"
href="https://bugs.llvm.org/show_bug.cgi?id=41348">41348</a>
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<th>Summary</th>
<td>[X86] Failure to move indvar constant offset into final address gen
</td>
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<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>andrea.dibiagio@gmail.com, craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<div>
<pre><a href="https://gcc.godbolt.org/z/Z2uB_v">https://gcc.godbolt.org/z/Z2uB_v</a>
<snip>
leal 1(%rdx), %eax
leaq (%rax,%rax,2), %rax
movq %r9, (%rdi,%rax,8)
leal 2(%rdx), %eax
leaq (%rax,%rax,2), %rax
movq %r11, (%rdi,%rax,8)
leal 3(%rdx), %eax
leaq (%rax,%rax,2), %rax
movq %rcx, (%rdi,%rax,8)
<snip>
leal 31(%rdx), %eax
leaq (%rax,%rax,2), %rax
movq %rcx, (%rdi,%rax,8)
It'd be much better to just do the "leaq (%rax,%rax,2), %rax" once without the
offset and add the constant offset into the memory op address. Even for
hardware that doesn't like complex LEA this should be a definite win.
Something like (I haven't thoroughly check the trunc/zext effects):
leaq (%rdx,%rdx,2), %eax
movq %r9, 3,(%rdi,%rax,8)
movq %r11, 6,(%rdi,%rax,8)
movq %rcx, 9(%rdi,%rax,8)
<snip>
movq %rcx, 93(%rdi,%rax,8)</pre>
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