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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [ARM] Unnecessary reloads from GOT"
href="https://bugs.llvm.org/show_bug.cgi?id=35221">35221</a>
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<th>Summary</th>
<td>[ARM] Unnecessary reloads from GOT
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<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>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: ARM
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>eugeni.stepanov@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>ARM backend fails to reuse the address of an external variable between basic
blocks and reloads it from GOT on each use.
# cat 1.c
extern char x;
void fail();
void f() {
if (x) fail();
if (x) fail();
if (x) fail();
}
# clang 1.c -O3 -target arm-linux-androideabi -c && objdump -drl 1.o
f():
0: e92d4800 push {fp, lr}
4: e1a0b00d mov fp, sp
8: e59f004c ldr r0, [pc, #76] ; 5c <f+0x5c>
c: e79f0000 ldr r0, [pc, r0]
10: e5d00000 ldrb r0, [r0]
14: e3500000 cmp r0, #0
18: 0a00000d beq 54 <f+0x54>
1c: ebfffffe bl 0 <fail>
1c: R_ARM_CALL fail
20: e59f0038 ldr r0, [pc, #56] ; 60 <f+0x60>
24: e79f0000 ldr r0, [pc, r0]
28: e5d00000 ldrb r0, [r0]
2c: e3500000 cmp r0, #0
30: 0a000007 beq 54 <f+0x54>
34: ebfffffe bl 0 <fail>
34: R_ARM_CALL fail
38: e59f0024 ldr r0, [pc, #36] ; 64 <f+0x64>
3c: e79f0000 ldr r0, [pc, r0]
40: e5d00000 ldrb r0, [r0]
44: e3500000 cmp r0, #0
48: 0a000001 beq 54 <f+0x54>
4c: e8bd4800 pop {fp, lr}
50: eafffffe b 0 <fail>
50: R_ARM_JUMP24 fail
54: e8bd4800 pop {fp, lr}
58: e12fff1e bx lr
5c: 00000048 .word 0x00000048
5c: R_ARM_GOT_PREL x
60: 00000034 .word 0x00000034
60: R_ARM_GOT_PREL x
64: 00000020 .word 0x00000020
64: R_ARM_GOT_PREL x</pre>
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