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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Null check elimination when callsite args are nonnull"
href="https://bugs.llvm.org/show_bug.cgi?id=39119">39119</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Null check elimination when callsite args are nonnull
</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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>int foo(char *d, char *s) {
int res = strncmp(d, s, 10);
if (!s)
abort();
return res;
}
Current -O3 IR:
define dso_local i32 @foo(i8* nocapture readonly %d, i8* readonly %s)
local_unnamed_addr #0 {
entry:
%tobool = icmp eq i8* %s, null
br i1 %tobool, label %if.then, label %if.end
if.then: ; preds = %entry
tail call void @abort() #3
unreachable
if.end: ; preds = %entry
%call = tail call i32 @strncmp(i8* %d, i8* nonnull %s, i64 10) #4
ret i32 %call
}
We somehow miss logic to remove "top level null check", if all uses of %s are
in "nonnull" places
---------------------------------------------
For similar code:
int foo(char *d, char *s) {
int res = strncmp(d, s, 10);
if (!s)
abort();
if (!d)
exit(1);
return res;
}
We get:
define dso_local i32 @foo(i8* readonly %d, i8* readonly %s) local_unnamed_addr
#0 {
entry:
%call = tail call i32 @strncmp(i8* %d, i8* %s, i64 10) #3
%tobool = icmp eq i8* %s, null
br i1 %tobool, label %if.then, label %if.end
if.then: ; preds = %entry
tail call void @abort() #4
unreachable
if.end: ; preds = %entry
%tobool1 = icmp eq i8* %d, null
br i1 %tobool1, label %if.then2, label %if.end3
if.then2: ; preds = %if.end
tail call void @exit(i32 1) #4
unreachable
if.end3: ; preds = %if.end
ret i32 %call
}
But if I change
%call = tail call i32 @strncmp(i8* %d, i8* %s, i64 10) #3
to
%call = tail call i32 @strncmp(i8* nonnull %d, i8* nonnull %s, i64 10) #3
Ran:
opt -O3 -enable-nonnull-arg-prop aa.ll -S
No eliminations :/ We need to propagate nonnull info more.</pre>
</div>
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