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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - LICM incorrectly hoists load because Instruction::mayThrow does not correctly handle invokes" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D24185&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=BPIem4qSzf9X_-q3qFddA3vjvEUGdTj_gmH1DUaP6i0&s=EhTH1lrGkoYyUWB2ExgQ6biGBlUzuz5MeSWTQdFr0Gw&e=">24185</a>
</td>
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<th>Summary</th>
<td>LICM incorrectly hoists load because Instruction::mayThrow does not correctly handle invokes
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>sanjoy@playingwithpointers.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>Running -licm on the following IR hoists the load of `%m` outside the loop.
This is incorrect because it is possible that @f throws something that does not
unwind to `%right` (because the exception's type does not match `@_ZTIi`).
Such a throw will exit the frame. Thus, the load from %ptr is not executed on
all paths through the loop and cannot be safely speculated.
As far as I can tell, the bug is in Instruction::mayThrow -- LLVM cannot
certify that an `invoke` does not throw without analyzing all of its
landingpads.
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.10.0"
@_ZTIi = external constant i8*
declare i32 @__gxx_personality_v0(...)
declare i32 @f(i32) readnone
define i32 @g(i32* %ptr) personality i8* bitcast (i32 (...)*
@__gxx_personality_v0 to i8*) {
entry:
br label %loop
loop:
%acc = phi i32 [ 0, %entry ], [ %acc.next, %merge ]
%x = invoke i32 @f(i32 %acc) to label %left unwind label %right
left:
br label %merge
right:
%v = landingpad { i8*, i32 } catch i8* bitcast (i8** @_ZTIi to i8*)
br label %merge
merge:
%vv = phi i32 [ %x, %left ], [ 0, %right]
%m = load i32, i32* %ptr
%acc.next = add i32 %m, %acc
%c = icmp eq i32 %vv, 0
br i1 %c, label %loop, label %exit
exit:
ret i32 %acc
}</pre>
</div>
</p>
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