<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/64566>64566</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
Dead Code Elimination Regression at -O2 (trunk vs. llvmorg-16.0.6)
</td>
</tr>
<tr>
<th>Labels</th>
<td>
new issue
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
SvenjaScherrer
</td>
</tr>
</table>
<pre>
```c
static int b, c, d;
static int e[][1] = {{}, {}, {}, {}, {}, 4, 6, 9};
static short f = 5;
static char g = 194;
static int *j = &e[7][0];
void bar18_(void);
void foo(void);
void bar20_(void);
static short(a)(short k) { return k; }
static void i();
static void h(short k) {
if (a(0)) {
c++;
e[c];
--f;
}
i(&d, k, g);
}
static void i(int *, int l, unsigned n) {
o:
*j = 0;
if (!(n >= 4294967234 && n <= 4294967234))
bar20_();
if (l)
bar18_();
{
int p;
if (!(n >= 4294967234 && n <= 4294967234))
foo();
n = 0;
for (; n <= 5; n++) {
int q;
if (0 == f)
goto o;
if (*j)
break;
}
}
}
int main() {
char m = b = 8;
for (; b; b--)
h(b);
a(m);
}
```
`clang-84e89c9e0640 (trunk) -O2` cannot eliminate the call to foo but `clang-llvmorg-16.0.6 -O2` can.
-----------------------------------------------------------------------
`clang-84e89c9e0640de4cb946d126723d2038b74e2ea0 -O2 case.c -S -emit-llvm -o case.ll`
<details ><summary>Emitted IR</summary><p>
```ll
; ModuleID = 'case.c'
source_filename = "case.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@b = internal unnamed_addr global i32 0, align 4
@e.0 = internal unnamed_addr global i1 false, align 16
; Function Attrs: nounwind uwtable
define dso_local i32 @main() local_unnamed_addr #0 {
store i32 8, ptr @b, align 4, !tbaa !5
br label %1
1: ; preds = %0, %16
%2 = phi i32 [ 8, %0 ], [ %18, %16 ]
%3 = and i32 %2, 65535
%4 = icmp eq i32 %3, 0
store i1 true, ptr @e.0, align 16
br i1 %4, label %8, label %5
5: ; preds = %1
tail call void @bar18_() #2
%6 = load i1, ptr @e.0, align 16
%7 = freeze i1 %6
br i1 %7, label %8, label %9
8: ; preds = %1, %5
br label %9
9: ; preds = %8, %5
%10 = phi i1 [ true, %8 ], [ false, %5 ]
%11 = phi i32 [ 0, %8 ], [ 3, %5 ]
switch i32 %11, label %12 [
i32 3, label %16
i32 0, label %16
]
12: ; preds = %9
br i1 %10, label %16, label %13
13: ; preds = %12
store i1 true, ptr @e.0, align 16
tail call void @bar20_() #2
br i1 %4, label %15, label %14
14: ; preds = %13
tail call void @bar18_() #2
br label %15
15: ; preds = %14, %13
tail call void @foo() #2
br label %16
16: ; preds = %15, %9, %9, %12
%17 = load i32, ptr @b, align 4, !tbaa !5
%18 = add nsw i32 %17, -1
store i32 %18, ptr @b, align 4, !tbaa !5
%19 = icmp eq i32 %18, 0
br i1 %19, label %20, label %1, !llvm.loop !9
20: ; preds = %16
ret i32 0
}
declare void @bar20_() local_unnamed_addr #1
declare void @bar18_() local_unnamed_addr #1
declare void @foo() local_unnamed_addr #1
attributes #0 = { nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #1 = { "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #2 = { nounwind }
!llvm.module.flags = !{!0, !1, !2, !3}
!llvm.ident = !{!4}
!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 8, !"PIC Level", i32 2}
!2 = !{i32 7, !"PIE Level", i32 2}
!3 = !{i32 7, !"uwtable", i32 2}
!4 = !{!"clang version 18.0.0 (git@github.com:llvm/llvm-project.git 84e89c9e0640de4cb946d126723d2038b74e2ea0)"}
!5 = !{!6, !6, i64 0}
!6 = !{!"int", !7, i64 0}
!7 = !{!"omnipotent char", !8, i64 0}
!8 = !{!"Simple C/C++ TBAA"}
!9 = distinct !{!9, !10}
!10 = !{!"llvm.loop.mustprogress"}
```
</p></details>
-----------------------------------------------------------------------
`clang-af2ed9f794c422923414d162dd1f48d986e2d6e3 -O2 case.c -S -emit-llvm -o case.ll`
<details ><summary>Emitted IR</summary><p>
```ll
; ModuleID = 'case.c'
source_filename = "case.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@b = internal unnamed_addr global i32 0, align 4
; Function Attrs: nounwind uwtable
define dso_local i32 @main() local_unnamed_addr #0 {
store i32 8, ptr @b, align 4, !tbaa !5
br label %1
1: ; preds = %0, %6
%2 = phi i32 [ 8, %0 ], [ %8, %6 ]
%3 = and i32 %2, 65535
%4 = icmp eq i32 %3, 0
br i1 %4, label %6, label %5
5: ; preds = %1
tail call void @bar18_() #2
br label %6
6: ; preds = %1, %5
%7 = load i32, ptr @b, align 4, !tbaa !5
%8 = add nsw i32 %7, -1
store i32 %8, ptr @b, align 4, !tbaa !5
%9 = icmp eq i32 %8, 0
br i1 %9, label %10, label %1, !llvm.loop !9
10: ; preds = %6
ret i32 0
}
declare void @bar18_() local_unnamed_addr #1
attributes #0 = { nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #1 = { "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #2 = { nounwind }
!llvm.module.flags = !{!0, !1, !2, !3}
!llvm.ident = !{!4}
!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 8, !"PIC Level", i32 2}
!2 = !{i32 7, !"PIE Level", i32 2}
!3 = !{i32 7, !"uwtable", i32 2}
!4 = !{!"clang version 16.0.6 (git@github.com:llvm/llvm-project.git 7cbf1a2591520c2491aa35339f227775f4d3adf6)"}
!5 = !{!6, !6, i64 0}
!6 = !{!"int", !7, i64 0}
!7 = !{!"omnipotent char", !8, i64 0}
!8 = !{!"Simple C/C++ TBAA"}
!9 = distinct !{!9, !10}
!10 = !{!"llvm.loop.mustprogress"}
```
</p></details>
-----------------------------------------------------------------------
Bisects to 72121a20cda4dc91d0ef5548f93046e71c5ec6f6
Committed by: @fhahn
</pre>
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