Fix stack overflow when asking for an AOT operand's type. #1397
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I've just noticed a small typo in the commit message. If we could pause before merging so I can fix it. |
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Please force push a fix. |
When adding more passes to the AOT pipeline we found that the mere act
of printing the AOT module can cause stack overflows.
If you have IR like:
```
bb0:
%1 = ...
bb1:
%2 = phi bb1 -> %3, bb0 -> %1
%3 = %2 + 1
goto bb1
```
Asking the type of %3 causes infinite recursion.
This is because an operation often asks its operands for their type to
determine their own type.
Here, %3 asks %2, who asks %3, who asks %2, who asks... forever. Each
"ask" is a function call, so this blows the stack.
This change breaks the cycle by putting a PHI's type into the
instruction explicitly, so it doesn't have to search further afield to
know it's type.
We haven't seen this before because usually the first operand to a PHI
is from earlier (not later) in the module, so there is no cycle.
|
Fixed. |
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Requires ykjit/ykllvm#200
When adding more passes to the AOT pipeline we found that the mere act of printing the AOT module can cause stack overflows.
If you have IR like:
Asking the type of %3 causes infinite recursion.
This is because an operation often asks its operands for their type to determine their own type.
Here, %3 asks %2, who asks %3, who asks %2, who asks... forever. Each "ask" is a function call, so this blows the stack.
This change breaks the cycle by putting a PHI's type into the instruction explicitly, so it doesn't have to search further afield to know it's type.
We haven't seen this before because usually the first operand to a PHI is from earlier (not later) in the module, so there is no cycle.