<html>
<head>
<base href="https://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 --- - MachineLICM register pressure calculation incorrect"
href="https://llvm.org/bugs/show_bug.cgi?id=23143">23143</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>MachineLICM register pressure calculation incorrect
</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>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>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>djasper@google.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>The new test test/CodeGen/X86/licm-regpressure.ll shows this behavior
(currently marked as XFAIL). MachineLICM assumes that it is hoisting all of the
GEPs out of the loop under in a low pressure situation, when indeed there is
register pressure.
The cause here is that the RegLimit (for the RegClass GR64) is 12, but each
instruction is assumed to have a cost of only 1.
The problem seems to be that MachineLICM isn't considering the regmasks, i.e.
the registers clobbered by the call.
IR leading to the bad behavior:
%struct.A = type { i32, i32, i32, i32, i32, i32, i32 }
define void @test(i1 %b, %struct.A* %a) nounwind {
entry:
br label %loop-header
loop-header:
br label %loop-body
loop-body:
%0 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 0
%1 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 1
%2 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 2
%3 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 3
%4 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 4
%5 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 5
%6 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 6
call void @assign(i32* %0)
call void @assign(i32* %1)
call void @assign(i32* %2)
call void @assign(i32* %3)
call void @assign(i32* %4)
call void @assign(i32* %5)
call void @assign(i32* %6)
br i1 %b, label %loop-body, label %loop-exit
loop-exit:
ret void
}
declare void @assign(i32*)</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>