<html>
<head>
<base href="https://bugs.llvm.org/">
</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 - Unnecessary spills when passing a struct argument by value"
href="https://bugs.llvm.org/show_bug.cgi?id=46798">46798</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Unnecessary spills when passing a struct argument by value
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</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>riyaz@synopsys.com
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=23763" name="attach_23763" title="C test case to reproduce the problem">attachment 23763</a> <a href="attachment.cgi?id=23763&action=edit" title="C test case to reproduce the problem">[details]</a></span>
C test case to reproduce the problem
Clang generates unnecessary spills of %xmm0 and %rax for the attached test
case. See below (and attached test) for details.
The issue goes away if an __attribute__((align(8)) is added to the variable
blah.
// Test case:
// compile: clang -O3 -S -emit-llvm -o test.s test.c
typedef struct { int a; int b; int c; int d; int e; int f; } T;
extern int foo(T a);
extern T blah;
int boo() {
return foo(blah);
}
Code generated by gcc:
subq $40, %rsp
movq blah+16(%rip), %rax
movdqu blah(%rip), %xmm0
movq %rax, 16(%rsp)
movups %xmm0, (%rsp)
call foo
addq $40, %rsp
ret
Code generated by "clang -O3"
subq $56, %rsp
movq blah+16(%rip), %rax
movq %rax, 48(%rsp) ; unnecessary
movups blah(%rip), %xmm0
movaps %xmm0, 32(%rsp) ; unnecessary
movq 48(%rsp), %rax ; unnecessary
movq %rax, 16(%rsp)
movaps 32(%rsp), %xmm0 ; unnecessary
movups %xmm0, (%rsp)
callq foo
addq $56, %rsp
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>