<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 - Bug in pass 'ipsccp' on function attribute 'argmemonly'."
href="https://bugs.llvm.org/show_bug.cgi?id=46717">46717</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Bug in pass 'ipsccp' on function attribute 'argmemonly'.
</td>
</tr>
<tr>
<th>Product</th>
<td>tools
</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>opt
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>fangqingdu@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>When pass 'ipsccp' replaces arguments with global variables, it forgets to
remove the function's 'argmemonly' attribute. Which may cause wrong behavior,
just like following test case(from Alexandre Isoard) shows:
********************************************************
; RUN: opt -ipsccp -deadargelim -licm -O2 -S < %s
@g = internal global i32 0
; Function Attrs: argmemonly
define internal void @foo(i32* nonnull dereferenceable(4) %arg, i32 %val) #0 {
entry:
store i32 %val, i32* %arg
ret void
}
define i32 @bar(i32 %n) {
entry:
store i32 1, i32* @g
br label %loop
loop: ; preds = %bb1, %bb
%i = phi i32 [ %i.inc, %loop ], [ 0, %entry ]
%g.val = load i32, i32* @g
%g.inc = add nuw i32 %g.val, 1
tail call void @foo(i32* @g, i32 %g.inc)
%i.inc = add nuw i32 %i, 1
%cond = icmp eq i32 %i.inc, %n
br i1 %cond, label %exit, label %loop
exit: ; preds = %bb1
ret i32 %g.val
}
declare void @llvm.assume(i1)
attributes #0 = { argmemonly }
********************************************************
Before 'ipsccp', function '@foo' is marked with 'argmemonly' attribute. But
after the argument '%arg' is replaced with '@g' by pass 'ipsccp', attribute
'argmemonly' is left there. And due to the 'argmemonly' attribute, pass 'licm'
will think the value of global variable '@g' is not changed (but it is
changed), then hoist the load of the '@g' outside the loop. And cause function
'@bar' return wrong value '1'. But the correct return value should be '%n'.</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>