[PATCH] Fix for CodeGenPrepare wrongly updating the map of sunk addresses

[Andrea_DiBiagio at sn.scee.net]

Friendly ping.

-- Andrea Di Biagio


Andrea DiBiagio/SN R&D/BS/UK/SCEE wrote on 12/04/2013 18:56:08:

> From: Andrea DiBiagio/SN R&D/BS/UK/SCEE
> To: llvm-commits at cs.uiuc.edu
> Date: 12/04/2013 18:56
> Subject: [PATCH] Fix for CodeGenPrepare wrongly updating the map of 
> sunk addresses
> 
> Hello,
> 
> I'd like to contribute a patch to fix a problem in Pass CodeGen Prepare.
> 
> Method OptimizeMemoryInst is not always able to correctly update 
DenseMap
> SunkAddrs by erasing no longer valid keys associated to Values which 
have
> been deleted in memory.
> 
> When method OptimizeMemoryInst calls function 
> `RecursivelyDeleteTriviallyDeadInstructions', potentially not all the
> dead keys are erased from the map SunkAddrs.
> Therefore, there are cases where map SunkAddrs is left in a inconsistent
> state where buckets associated to keys of deleted Values are 
> still considered to be valid.
> 
> This can be problematic for example in the following scenario where:
> 1. A new Instruction I created to replace the address expression for a 
>    load or store instruction;
> 2. address of I is the same as a previously deleted Value
>    pointed to by a key K of map SunkAddrs;
> 3. K is still a valid key in SunkAddrs.
> 
> CodeGenPrepare may think that occurrence of address I could be replaced
> with the Value returned by SunkAddrs[I] which is however invalid.
> 
> PROPOSED FIX
> ------------
> With this patch, CodeGenPrepare now uses a CallbackVH as the key of
> map SunkAddrs. Each CallbackVH is able to monitor changes in the
> state of a specific key Value. When a key is deleted by
> method RecursivelyDeleteTriviallyDeadInstructions its associated
> CallbackVH is notified and the corresponding entry in SunkAddrs
> is correctly erased.
> I also added an x86 specific test case that exposes the problem 
> found in CodeGenPrepare.
> 
> Thanks!
> -- Andrea Di Biagio


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