<html>
<head>
<base href="http://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 --- - Devirtualization fails for loop, while succeeds for a scalar call of the same method"
href="http://llvm.org/bugs/show_bug.cgi?id=20801">20801</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Devirtualization fails for loop, while succeeds for a scalar call of the same method
</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>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>zinovy.nis@gmail.com
</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><span class="quote">> clang++ -v</span >
clang version 3.6.0
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/i686-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
<span class="quote">> cat test.cpp</span >
class A { public: virtual int f() { return 123;} };
int Scalar() { A* a = new A; return a->f(); }
int Vector(int N) { A* a = new A; int sum = 0; for(int i = 0; i < N; ++i) sum
+= a->f(); return sum; }
int main(int argc, char** argv) { return Scalar() + Vector(argc); }
<span class="quote">> clang++ -march=core-avx2 -Ofast test.cpp -S -o - | c++filt | less</span >
...
Scalar():
movl $123, %eax # <<<----- devirtualized!
retq
Vector(int):
pushq %rbp
pushq %r14
pushq %rbx
movl %edi, %ebx
movl $8, %edi
callq operator new(unsigned long) # <<<<----- it's new is not needed
movq %rax, %r14
movq vtable for A+16, (%r14)
xorl %eax, %eax
testl %ebx, %ebx
jle .LBB1_4
# BB#1: # %for.body.lr.ph
xorl %eax, %eax
movl vtable for A+16, %ecx
jmp .LBB1_2
.align 16, 0x90
.LBB1_3: # %for.body.for.body_crit_edge
# in Loop: Header=BB1_2 Depth=1
movq (%r14), %rcx
.LBB1_2: # %for.body
# =>This Inner Loop Header: Depth=1
movl %eax, %ebp
movq %r14, %rdi
callq *(%rcx) # <<<<<----- virtual call!
addl %ebp, %eax
decl %ebx
jne .LBB1_3
.LBB1_4: # %for.end
popq %rbx
popq %r14
popq %rbp
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>