<html>
<head>
<base href="https://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Less efficient stack adjustment code with -g"
href="https://llvm.org/bugs/show_bug.cgi?id=23240">23240</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Less efficient stack adjustment code with -g
</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>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>russell_gallop@sn.scee.net
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Enabling debug info results in larger code at address 0x13. Without -g a 1 byte
pop instruction is used, with -g a 4 byte add is used to adjust the stack
pointer. Guessing that this is in the X86 backend.
Reduced from Burg in the llvm-test-suite. With revision r234984.
$ cat lex.c
int a;
int fn2();
int fn1() {
int b;
if ((b = fn2()) == '\n')
a++;
return b;
}
$ clang -c -O1 lex.c -o lex.o && objdump -d lex.o
lex.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <fn1>:
0: 50 push %rax
1: 31 c0 xor %eax,%eax
3: e8 00 00 00 00 callq 8 <fn1+0x8>
8: 83 f8 0a cmp $0xa,%eax
b: 75 06 jne 13 <fn1+0x13>
d: ff 05 00 00 00 00 incl 0x0(%rip) # 13 <fn1+0x13>
13: 5a pop %rdx
14: c3 retq
$ clang -c -O1 lex.c -o lex_g.o -g && objdump -d lex_g.o
lex_g.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <fn1>:
0: 50 push %rax
1: 31 c0 xor %eax,%eax
3: e8 00 00 00 00 callq 8 <fn1+0x8>
8: 83 f8 0a cmp $0xa,%eax
b: 75 06 jne 13 <fn1+0x13>
d: ff 05 00 00 00 00 incl 0x0(%rip) # 13 <fn1+0x13>
13: 48 83 c4 08 add $0x8,%rsp
17: c3 retq</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>