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<head>
<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 - Regression: const function hoisting not happening"
href="https://bugs.llvm.org/show_bug.cgi?id=34208">34208</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Regression: const function hoisting not happening
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</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>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nat-llvmbugs@mulle-kybernetik.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Starting with 3.9.0 a const function is not hoisted out of the loop anymore.
Compiling this little C snippet
```
extern __attribute__(( const)) int foo( int i);
extern int bar( int i);
int foobar( void)
{
int i;
int x;
x = 0;
for( i = 0; i < 100; i++)
{
x += foo( 0x2373);
x = bar( x);
}
return( x == 1848);
}
```
with `-O3 -S -emit-llvm` produces
```
; ModuleID = '/tmp/x.c'
source_filename = "/tmp/x.c"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-freebsd10.3"
; Function Attrs: nounwind uwtable
define i32 @foobar() local_unnamed_addr #0 {
br label %1
; <label>:1: ; preds = %1, %0
%2 = phi i32 [ 0, %0 ], [ %6, %1 ]
%3 = phi i32 [ 0, %0 ], [ %7, %1 ]
%4 = tail call i32 @foo(i32 9075) #3
%5 = add nsw i32 %4, %2
%6 = tail call i32 @bar(i32 %5) #4
%7 = add nuw nsw i32 %3, 1
%8 = icmp eq i32 %7, 100
br i1 %8, label %9, label %1
; <label>:9: ; preds = %1
%10 = icmp eq i32 %6, 1848
%11 = zext i1 %10 to i32
ret i32 %11
}
; Function Attrs: nounwind readnone
declare i32 @foo(i32) local_unnamed_addr #1
declare i32 @bar(i32) local_unnamed_addr #2
attributes #0 = { nounwind uwtable "disable-tail-calls"="false"
"less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
"no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
"no-jump-tables"="false" "no-nans-fp-math"="false"
"no-signed-zeros-fp-math"="false" "stack-protector-buffer-size"="8"
"target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87"
"unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { nounwind readnone "disable-tail-calls"="false"
"less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
"no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
"no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false"
"stack-protector-buffer-size"="8" "target-cpu"="x86-64"
"target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false"
"use-soft-float"="false" }
attributes #2 = { "disable-tail-calls"="false" "less-precise-fpmad"="false"
"no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false" "no-nans-fp-math"="false"
"no-signed-zeros-fp-math"="false" "stack-protector-buffer-size"="8"
"target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87"
"unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #3 = { nounwind readnone }
attributes #4 = { nounwind }
!llvm.ident = !{!0}
!0 = !{!"clang version 3.9.0 (tags/RELEASE_390/final)"}
```
But with clang 3.8.1 it hoists the function `foo` correctly out of the loop:
```
; ModuleID = 'x.c'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-freebsd10.3"
; Function Attrs: nounwind uwtable
define i32 @foobar() #0 {
entry:
%call = tail call i32 @foo(i32 9075) #3
br label %for.body
for.body: ; preds = %for.body, %entry
%x.09 = phi i32 [ 0, %entry ], [ %call1, %for.body ]
%i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%add = add nsw i32 %call, %x.09
%call1 = tail call i32 @bar(i32 %add) #4
%inc = add nuw nsw i32 %i.08, 1
%exitcond = icmp eq i32 %inc, 100
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body
%call1.lcssa = phi i32 [ %call1, %for.body ]
%cmp2 = icmp eq i32 %call1.lcssa, 1848
%conv = zext i1 %cmp2 to i32
ret i32 %conv
}
; Function Attrs: nounwind readnone
declare i32 @foo(i32) #1
declare i32 @bar(i32) #2
attributes #0 = { nounwind uwtable "disable-tail-calls"="false"
"less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
"no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
"no-nans-fp-math"="false" "stack-protector-buffer-size"="8"
"target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2"
"unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { nounwind readnone "disable-tail-calls"="false"
"less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
"no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
"no-nans-fp-math"="false" "stack-protector-buffer-size"="8"
"target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2"
"unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { "disable-tail-calls"="false" "less-precise-fpmad"="false"
"no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false" "no-nans-fp-math"="false"
"stack-protector-buffer-size"="8" "target-cpu"="x86-64"
"target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false"
"use-soft-float"="false" }
attributes #3 = { nounwind readnone }
attributes #4 = { nounwind }
!llvm.ident = !{!0}
!0 = !{!"clang version 3.8.1 (tags/RELEASE_381/final)"}
```
If you remove the line `x = bar( x);` from the loop, the optimizer doesn't have
the problem anymore.
P.S. Do not use <a href="https://godbolt.org">https://godbolt.org</a> to test this, for some reasons it gives
different results.</pre>
</div>
</p>
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