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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - ARM: integrated assembler should replace "ldr rX, =imm" with "mov rX, #imm" if imm can be encoded as immediate"
href="https://llvm.org/bugs/show_bug.cgi?id=25722">25722</a>
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<tr>
<th>Summary</th>
<td>ARM: integrated assembler should replace "ldr rX, =imm" with "mov rX, #imm" if imm can be encoded as immediate
</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>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: ARM
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nicolasweber@gmx.de
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>gas does that, it produces smaller code, and it prevents follow-on "out of
range pc-relative fixup value" errors if the ldr is in a large-ish code block
and the offset to the constant pool is too large.
Example (reduced from boringssl):
thakis@thakis:~/src/chrome/src$ head arm.S
.fpu neon
.text
.align 4
.global foo
.hidden foo
.type foo, %function
ldr r4, =0
mov r1, r2
mov r1, r2
/* repeat previous instruction 2000 times here */
thakis@thakis:~/src/chrome/src$
third_party/llvm-build/Release+Asserts/bin/clang -c arm.S -march=armv7-a
-target arm-linux-androideab
arm.S:8:1: error: out of range pc-relative fixup value
ldr r4, =0
^
thakis@thakis:~/src/chrome/src$
third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc
-c arm.S
thakis@thakis:~/src/chrome/src$
third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/linux-x86_64/bin/arm-linux-androideabi-objdump
-D -marm arm.o | head
arm.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <.text>:
0: e3a04000 mov r4, #0
4: e1a01002 mov r1, r2
8: e1a01002 mov r1, r2</pre>
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