[PATCH] D145168: Move DBG_VALUE's that depend on loads to after a load if the load is moved due to the pre register allocation ld/st optimization pass

[Shubham Sandeep Rastogi via Phabricator via llvm-commits]

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The issue here is that there can be a scenario where debug information is lost because of the pre register allocation load store optimization pass, where a load who's result describes the debug infomation for a local variable gets moved below the load and that causes the debug information for that load to get lost.

  
  Example:
  
  Before the Pre Register Allocation Load Store Pass
  inst_a
  %2 = ld ...
  inst_b
  DBG_VALUE %2, "x", ...
  %3 = ld ...
  
  After the Pass:
  inst_a
  inst_b
  DBG_VALUE %2, "x", ...
  %2 = ld ...
  %3 = ld ...
  
  The load has now been moved to after the DBG_VAL that uses its result and the debug info for "x" has been lost. What we want is:
  
  inst_a
  inst_b
  %2 = ld ...
  DBG_VALUE %2, "x", ...
  %3 = ld ...
  
  Which is what this patch addresses


https://reviews.llvm.org/D145168

Files:
  llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
  llvm/test/DebugInfo/ARM/move-dbg-values.mir

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