[PATCH] D58403: [DebugInfo][CGP] Update dbg.values when updating memory address computations

[Bjorn Pettersson via Phabricator via llvm-commits]

bjope added inline comments.


================
Comment at: lib/CodeGen/CodeGenPrepare.cpp:4938
+    // Discard debug users in other blocks.
+    if (User->getParent() != MemoryInst->getParent())
+      continue;
----------------
What happens if there is an earlier dbg-use of Repl (before MemoryInst) in this BB. Is there a risk that we introduce a dbguse-before-def scenario here? Maybe we need to check if MemoryInst dominates User here? Or is such input IR unlikely in reality? 

There seems to be lots of cases above (for example reusing an earlier computation for SunkAddr), so maybe the important check is that SunkAddr dominates User. But as you understand from the question marks above, I haven't figured out if that always is guaranteed here.

Notice that I do not think about scenarios when the input IR already is "broken" (dgb-use before def) here. Just some worrying that we might introduce dbg-use-before-def here.

Actually the test case that you added has the dbg.value before the load in the BB that we sink the address computation into (the scenario I'm talking about). Isn't the address computation added just before the load? Is perhaps the test case working due to placeDbgValues moving the dbg.value?


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  rL LLVM

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  https://reviews.llvm.org/D58403/new/

https://reviews.llvm.org/D58403