passManager should always call releaseMemory to avoid use-after-free bugs

[edwintorok]

Bugzilla Link	4398
Resolution	FIXED
Resolved on	Mar 02, 2010 11:32
Version	unspecified
OS	Linux
Attachments	passmanager patch, testcase
CC	@sunfishcode

Extended Description

Currently some passes call releaseMemory (or their equivalent) in their run function, some don't (for example ScalarEvolution).

According to the documentation "This method is called after the run* method for the class, before the next call of run* in your pass."

However the PassManager doesn't do this for on-the-fly passes, which can cause use-after-free bugs if you are using ScalarEvolution from a ModulePass
(LoopInfo is rerun, but ScalarEvolution still has stale data from the previous LoopInfo run).

As discusses on llvm-commits the following should happen:

• PassManager should call releaseMemory for on-the-fly passes too
• PassManager should assert if it forgot to call releaseMemory
• passes that have a releaseMemory equivalent should have the method renamed to releaseMemory
• passes should no longer call releaseMemory in their run function

[edwintorok]

assigned to @edwintorok

[llvmbot]

Watch out for extra white spaces in the patch. Do you really need wasRun? Isn't Changed enough ? Otherwise the patch looks good.

[edwintorok]

Watch out for extra white spaces in the patch.

I'll clean them up.

Do you really need wasRun? Isn't
Changed enough ?

wasRun is needed to make sure that releaseMemory isn't called before the first
call to run(), and that it is called after the first call to run().

Changed isn't always set to true after a run(), and yet the pass could have allocated memory.

Otherwise the patch looks good.

Thanks, I'll apply the patch.

[sunfishcode]

The patch is applied, right? Is this bug fixed?

[edwintorok]

The patch is applied, right? Is this bug fixed?

I should've closed the bug after applying the patch, thanks for reminding.