[llvm-dev] DBG_VALUE insertion for spills breaks bundles

[Adrian Prantl via llvm-dev]

Thank you for your patch. Could you please add a testcase to it and upload it to reviews.llvm.org and CC llvm-commits, me and the debug-info group?

-- adrian

> On Dec 22, 2017, at 6:28 AM, Verma, Saurabh via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi again,
>  
> Here is a small patch to fix this issue.  Please note that since the problem results in broken bundles, it can result in invalid schedules for any VLIW back-ends using bundling to group instructions.
>  
> Best regards
> Saurabh Verma
>  
> From: Verma, Saurabh 
> Sent: Tuesday, December 19, 2017 4:14 PM
> To: llvm-dev at lists.llvm.org
> Subject: DBG_VALUE insertion for spills breaks bundles
>  
> Hi,
>  
> The insertion of DBG_VALUE instructions for spills does not seem to be handling insert locations inside bundles well. If the spill instruction is part of a bundle, the new DBG_VALUE is inserted after it, but does not have the bundling flags set. This essentially means that if we start with a set of bundled instructions:
>  
> MI1 [BundledSucc=true,  BundledPred=false]
> MI2 [BundledSucc=false, BundledPred=true]
>  
> Where MI1 is a spill, and MI2 is a different instruction, after ExtendRanges we end up with
>  
> MI1 [BundledSucc=true,  BundledPred=false]
> DBG_VALUE MI [BundledSucc=false,  BundledPred=false]
> MI2 [BundledSucc=false, BundledPred=true]
>  
> Since this happens after the final instruction scheduling, it results in broken schedules. I believe setting the bundling flags before invoking MBB->insertAfter in ExtendRanges should fix this.
>  
> Best regards
> Saurabh Verma
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