| Issue |
83469
|
| Summary |
[Pass Manager] Infinite loop of scheduled passes
|
| Labels |
|
| Assignees |
|
| Reporter |
patrick-rivos
|
Affects LLVM 13 up to and including trunk.
Program:
```c
short a, b;
signed char c;
short d[52];
static char e() {
for (;; b--) {
a = 0;
for (; a <= 3; a++) {
c = 2;
for (; c >= 0; c--)
if ((short)(b * (c + 1) * 4))
if (d[c * 4 + a])
return 0;
}
}
}
void f() { e(); }
```
Godbolt: https://godbolt.org/z/hKcezobh8
Reduced LLVM IR:
```llvm ir
@b = external global i16
@c = external global i8
@d = external global [52 x i16]
define void @f() {
entry:
%call = call i8 @e()
ret void
}
define internal i8 @e() {
entry:
br label %for.cond
for.cond: ; preds = %for.inc21, %entry
br label %for.cond1
for.cond1: ; preds = %for.inc19, %for.cond
%0 = phi i16 [ 0, %for.cond ], [ %inc, %for.inc19 ]
%cmp = icmp slt i16 %0, 4
br i1 %cmp, label %for.cond3, label %for.inc21
for.cond3: ; preds = %for.inc, %for.cond1
%1 = phi i8 [ %dec, %for.inc ], [ 2, %for.cond1 ]
store i8 %1, ptr @c, align 1
%cmp5 = icmp sgt i8 %1, -1
br i1 %cmp5, label %for.body7, label %for.inc19
for.body7: ; preds = %for.cond3
%2 = load i16, ptr @b, align 2
%narrow = add i8 %1, 1
%add = zext i8 %narrow to i16
%mul = mul i16 %2, %add
%mul10.mask = and i16 %mul, 16383
%tobool.not = icmp eq i16 %mul10.mask, 0
br i1 %tobool.not, label %for.inc, label %if.then
if.then: ; preds = %for.body7
%conv12 = zext i8 %1 to i32
%mul13 = shl i32 %conv12, 2
%conv14 = sext i16 %0 to i32
%add15 = or i32 %mul13, %conv14
%idxprom = sext i32 %add15 to i64
%arrayidx = getelementptr [52 x i16], ptr @d, i64 0, i64 %idxprom
%3 = load i16, ptr %arrayidx, align 2
%tobool16.not = icmp eq i16 %3, 0
br i1 %tobool16.not, label %for.inc, label %if.then17
if.then17: ; preds = %if.then
ret i8 0
for.inc: ; preds = %if.then, %for.body7
%dec = add i8 %1, -1
br label %for.cond3
for.inc19: ; preds = %for.cond3
%inc = add i16 %0, 1
br label %for.cond1
for.inc21: ; preds = %for.cond1
%4 = load i16, ptr @b, align 2
%dec22 = add i16 %4, 1
store i16 %dec22, ptr @b, align 2
br label %for.cond
}
```
Godbolt: https://godbolt.org/z/xzr8bEx8W
>From `-opt-bisect-limit=3000` it seems like it gets into a loop with these 6 passes:
```
SimpleLoopUnswitchPass on for.inc.i.us186.us3650.us.us.us
LoopInstSimplifyPass on for.inc.i.us186.us3650.us.us.us
LoopSimplifyCFGPass on for.inc.i.us186.us3650.us.us.us
LICMPass on for.inc.i.us186.us3650.us.us.us
LoopRotatePass on for.inc.i.us186.us3650.us.us.us
LICMPass on for.inc.i.us186.us3650.us.us.us
... (repeat)
```
Found via fuzzer.
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