<html>
<head>
<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 - Missed load elimination"
href="https://bugs.llvm.org/show_bug.cgi?id=49924">49924</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed load elimination
</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>Windows NT
</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>struct A
{
int x;
} *A_ptr;
struct B
{
struct A a;
int y;
} *B_ptr;
int
test ()
{
struct A ap = { 0 };
B_ptr->y = 123;
*A_ptr = ap;
return B_ptr->y;
}
ICC/GCC:
test():
mov rax, QWORD PTR B_ptr[rip] #15.3
mov rdx, QWORD PTR A_ptr[rip] #16.4
mov DWORD PTR [4+rax], 123 #15.3
mov eax, 123 #17.10
mov DWORD PTR [rdx], 0 #16.4
ret #17.10
A_ptr:
B_ptr:
LLVM trunk:
test(): # @test()
mov rax, qword ptr [rip + B_ptr]
mov dword ptr [rax + 4], 123
mov rax, qword ptr [rip + A_ptr]
mov dword ptr [rax], 0
mov rax, qword ptr [rip + B_ptr]
mov eax, dword ptr [rax + 4]
ret
A_ptr:
.quad 0
B_ptr:
.quad 0
<a href="https://godbolt.org/z/Pxx66j44r">https://godbolt.org/z/Pxx66j44r</a></pre>
</div>
</p>
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