[llvm-dev] DBG_VALUE insertion for spills breaks bundles

[Verma, Saurabh via llvm-dev]

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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