[llvm] r309651 - [StackColoring] Update AliasAnalysis information in stack coloring pass

[Matthias Braun via llvm-commits]

This is going a little fast, given that Hal had raised concerns and the patch went in before he responded (at least it looks like that in phab). I'd like to hear his opinion first, given that my experience with alias analysis in LLVM is limited.

- Matthias

> On Aug 1, 2017, at 10:15 AM, Hans Wennborg via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Matthias, the PR for this was marked as a release blocker for 5.0.
> What do you think about merging this?
> 
> On Mon, Jul 31, 2017 at 8:32 PM, Hiroshi Inoue via llvm-commits
> <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
>> Author: inouehrs
>> Date: Mon Jul 31 20:32:15 2017
>> New Revision: 309651
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=309651&view=rev
>> Log:
>> [StackColoring] Update AliasAnalysis information in stack coloring pass
>> 
>> Stack coloring pass need to maintain AliasAnalysis information when merging stack slots of different types.
>> Actually, there is a FIXME comment in StackColoring.cpp
>> 
>> // FIXME: In order to enable the use of TBAA when using AA in CodeGen,
>> // we'll also need to update the TBAA nodes in MMOs with values
>> // derived from the merged allocas.
>> 
>> But, TBAA has been already enabled in CodeGen without fixing this pass.
>> The incorrect TBAA metadata results in recent failures in bootstrap test on ppc64le (PR33928) by allowing unsafe instruction scheduling.
>> Although we observed the problem on ppc64le, this is a platform neutral issue.
>> 
>> This patch makes the stack coloring pass maintains AliasAnalysis information when merging multiple stack slots.
> 
> (This is https://reviews.llvm.org/D35907 <https://reviews.llvm.org/D35907>)
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