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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - DSE fails to shorten sizes of memsets"
href="https://bugs.llvm.org/show_bug.cgi?id=50120">50120</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>DSE fails to shorten sizes of memsets
</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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre><a href="https://godbolt.org/z/48TT9dPvP">https://godbolt.org/z/48TT9dPvP</a>
#include <string.h>
struct pam {
void *p1;
void *p2;
#ifdef LONG
unsigned long size;
#else
unsigned int size;
unsigned int pad;
#endif
};
extern int use(struct pam *param);
unsigned int foo(void) {
struct pam s_pam;
memset(&s_pam, 0, sizeof(struct pam));
s_pam.size = 1;
return use(&s_pam);
}
For LONG case DSE changes 24->16
call void @llvm.memset.p0i8.i64(i8* noundef nonnull align 8
dereferenceable(24) %2, i8 0, i64 16, i1 false), !dbg !24
For INT case - no change - 24->24
call void @llvm.memset.p0i8.i64(i8* noundef nonnull align 8
dereferenceable(24) %2, i8 0, i64 24, i1 false), !dbg !23
INT case:
foo(): # @foo()
sub rsp, 24
xorps xmm0, xmm0
movaps xmmword ptr [rsp], xmm0
mov qword ptr [rsp + 16], 0 // ******
mov dword ptr [rsp + 16], 1 // ******
mov rdi, rsp
call use(pam*)
add rsp, 24
ret
LONG case:
foo(): # @foo()
sub rsp, 24
xorps xmm0, xmm0
movaps xmmword ptr [rsp], xmm0
mov qword ptr [rsp + 16], 1 // ******
mov rdi, rsp
call use(pam*)
add rsp, 24
ret</pre>
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