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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - wrong code after "opt -mem2reg -jump-threading -loop-unswitch -ipsccp -loop-extract-single -functionattrs""
href="https://bugs.llvm.org/show_bug.cgi?id=41511">41511</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>wrong code after "opt -mem2reg -jump-threading -loop-unswitch -ipsccp -loop-extract-single -functionattrs"
</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>cszide@163.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=21784" name="attach_21784" title=".bc file of the source code">attachment 21784</a> <a href="attachment.cgi?id=21784&action=edit" title=".bc file of the source code">[details]</a></span>
.bc file of the source code
$clang -v
clang version 9.0.0 (trunk 355281)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/jack-zhou/Documents/llvm/llvm_truck/llvm/build4/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
For the following code small.c, after running "opt -mem2reg -jump-threading
-loop-unswitch -ipsccp -loop-extract-single -functionattrs", lli and clang have
different outputs.
-----------------------------------------------------------
#include <stdio.h>
int a, b;
int main() {
c:
for (; a <= 1; a++) {
int d;
if (d)
goto c;
}
printf("%d\n",a);
}
-----------------------------------------------------------
$clang small.c -o small1.out && ./small1.out
2
$gcc small.c -o small2.out && ./small2.out
2
$clang -O3 -c -emit-llvm -mllvm -disable-llvm-optzns small.c -o small.bc
$opt -mem2reg -jump-threading -loop-unswitch -ipsccp -loop-extract-single
-functionattrs small.bc -o small-opt1.bc
By using lli, the program will never terminate.
$timeout -s 9 120 lli ./small-opt1.bc
Killed
However, when using clang to produce the executable file, the output is empty.
$clang small-opt1.bc -o small3.out && timeout -s 9 120 ./small3.out
Nothing here.
IR before optimzation
--------------------------------------------------------
@a = common dso_local global i32 0, align 4
@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
@b = common dso_local global i32 0, align 4
; Function Attrs: nounwind uwtable
define dso_local i32 @main() #0 {
%1 = alloca i32, align 4
%2 = alloca i32, align 4
%3 = alloca i32, align 4
store i32 0, i32* %1, align 4
br label %4
; <label>:4: ; preds = %14, %0
br label %5
; <label>:5: ; preds = %18, %4
%6 = load i32, i32* @a, align 4, !tbaa !2
%7 = icmp sle i32 %6, 1
br i1 %7, label %8, label %21
; <label>:8: ; preds = %5
%9 = bitcast i32* %2 to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* %9) #3
%10 = load i32, i32* %2, align 4, !tbaa !2
%11 = icmp ne i32 %10, 0
br i1 %11, label %12, label %13
; <label>:12: ; preds = %8
store i32 2, i32* %3, align 4
br label %14
; <label>:13: ; preds = %8
store i32 0, i32* %3, align 4
br label %14
; <label>:14: ; preds = %13, %12
%15 = bitcast i32* %2 to i8*
call void @llvm.lifetime.end.p0i8(i64 4, i8* %15) #3
%16 = load i32, i32* %3, align 4
switch i32 %16, label %25 [
i32 0, label %17
i32 2, label %4
]
; <label>:17: ; preds = %14
br label %18
; <label>:18: ; preds = %17
%19 = load i32, i32* @a, align 4, !tbaa !2
%20 = add nsw i32 %19, 1
store i32 %20, i32* @a, align 4, !tbaa !2
br label %5
; <label>:21: ; preds = %5
%22 = load i32, i32* @a, align 4, !tbaa !2
%23 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x
i8]* @.str, i64 0, i64 0), i32 %22)
%24 = load i32, i32* %1, align 4
ret i32 %24
; <label>:25: ; preds = %14
unreachable
}
---------------------------------------------------------------
IR after optimization
---------------------------------------------------------------
@a = common dso_local global i32 0, align 4
@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
@b = common dso_local global i32 0, align 4
; Function Attrs: nounwind uwtable
define dso_local i32 @main() #0 {
%.pr.pr = load i32, i32* @a, align 4, !tbaa !2
%1 = icmp sle i32 %.pr.pr, 1
br i1 %1, label %..split_crit_edge, label %..split1_crit_edge
..split1_crit_edge: ; preds = %0
br label %.split1
..split_crit_edge: ; preds = %0
br label %.split
.split: ; preds = %..split_crit_edge
br label %codeRepl
codeRepl: ; preds = %.split
call void @main.extracted()
ret i32 0
.split1: ; preds = %..split1_crit_edge
%2 = load i32, i32* @a, align 4, !tbaa !2
%3 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x
i8]* @.str, i64 0, i64 0), i32 %2)
ret i32 0
}
; Function Attrs: norecurse noreturn nounwind readnone uwtable
define internal void @main.extracted() #3 {
newFuncRoot:
br label %0
; <label>:0: ; preds = %newFuncRoot, %1
br label %1
; <label>:1: ; preds = %0
br label %0
}
Obviously, there is an infinite loop after optimization, lli chooses the
execute path with this infinite loop, but clang does not choose this path.</pre>
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