| Issue |
130110
|
| Summary |
`isGuaranteedNotToBeUndefOrPoison` is taking too long to execute
|
| Labels |
slow-compile,
llvm:optimizations,
missed-optimization,
llvm:analysis
|
| Assignees |
DianQK
|
| Reporter |
DianQK
|
Using the script can reproduce this:
```sh
#!/usr/bin/env bash
num_switches="$1"
cat <<EOF
define i64 @foo(i64 noundef %i) {
start:
br label %loop
loop:
EOF
echo -n " %nonpoison = phi i64 [ 0, %start ]"
for i in $(seq 0 $((num_switches - 1))); do
echo -n ", [ %nonpoison, %bb$i ]"
done
echo ", [ %nonpoison, %bb ], [ %i, %back_to_loop ]"
cat <<EOF
switch i64 %i, label %exit0 [
i64 -1, label %exit1
i64 2, label %back_to_loop
i64 0, label %bb
]
exit0:
br label %exit1
exit1:
%r = phi i64 [ %nonpoison, %loop ], [ undef, %exit0 ]
ret i64 %r
back_to_loop:
br label %loop
bb:
switch i64 %nonpoison, label %loop [
EOF
for i in $(seq 0 $((num_switches - 1))); do
echo " i64 $i, label %bb$i"
done
cat <<EOF
]
EOF
for i in $(seq 0 $((num_switches - 1))); do
echo "bb$i:"
echo " br label %loop"
done
echo "}"
```
```sh
./gen.sh 50 | opt -passes=instsimplify --disable-output
```
This is primarily due to a recursive check we're performing on a phi node that contains itself:
`%nonpoison = phi i64 [ 0, %start ], [ %nonpoison, %bb0 ], [ %nonpoison, %bb1 ], [ %nonpoison, %bb2 ], [ %nonpoison, %bb3 ], ..., [ %nonpoison, %bbn ], [ %nonpoison, %bb ], [ %i, %back_to_loop ]`.
The following code explains why returning true after exceeding the recursion depth:
https://github.com/llvm/llvm-project/blob/d6c0839c9c823754fb84e47c5bacf1a3b3d0f618/llvm/lib/Analysis/ValueTracking.cpp#L7885-L7889
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