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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 - [AArch64] redundant adrp/ldr on aarch64 (GCC does better)"
href="https://bugs.llvm.org/show_bug.cgi?id=39170">39170</a>
</td>
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<tr>
<th>Summary</th>
<td>[AArch64] redundant adrp/ldr on aarch64 (GCC does better)
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kcc@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>clang version 8.0.0 (trunk 343550)
typedef struct {
long a, b;
} S;
void foo(S *s) {
s->a = 1;
s->b = 0;
}
clang++ -fomit-frame-pointer -O3 -S -o - store16.c -target aarch64-linux
adrp x8, .LCPI0_0 <<<<<<<<<<<<
ldr q0, [x8, :lo12:.LCPI0_0] <<<<<<<<<<<<
str q0, [x0]
ret
While gcc 6.3 does this (much nicer!!):
mov x1, 1
stp x1, xzr, [x0]
ret
If I change "s->b = 0" to "s->b = 1" clang generates the same code
(loads the constant)
but gcc keeps avoiding loads (still better!!)
mov x2, 1
mov x1, 2
stp x2, x1, [x0]
ret</pre>
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