[PATCH] D64936: [Local] Zap blockaddress without users in ConstantFoldTerminator.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: craig.topper, brzycki, davide.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

If the blockaddress is not destoryed, the destination block will still
be marked as having its address taken, limiting further transformations.

I think there are other places where the dead blockaddress constants are kept
around, I'll look into that as follow up.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D64936

Files:
  llvm/lib/Transforms/Utils/Local.cpp
  llvm/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll


Index: llvm/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll
===================================================================
--- llvm/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll
+++ llvm/test/Transforms/SimplifyCFG/dce-cond-after-folding-terminator.ll
@@ -37,10 +37,7 @@
 entry:
 ; CHECK-LABEL: @test_indirectbr(
 ; CHECK-NEXT: entry:
-; Ideally this should now check:
-;   CHK-NEXT: ret void
-; But that doesn't happen yet. Instead:
-; CHECK-NEXT: br label %L1
+; CHECK-NEXT:   ret void
 
   %label = bitcast i8* blockaddress(@test_indirectbr, %L1) to i8*
   indirectbr i8* %label, [label %L1, label %L2]
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -324,8 +324,14 @@
       Value *Address = IBI->getAddress();
       IBI->eraseFromParent();
       if (DeleteDeadConditions)
+        // Delete pointer cast instructions.
         RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
 
+      // Also zap the blockaddress constant if there are no users remaining,
+      // otherwise the destination is still marked as having its address taken.
+      if (BA->use_empty())
+        BA->destroyConstant();
+
       // If we didn't find our destination in the IBI successor list, then we
       // have undefined behavior.  Replace the unconditional branch with an
       // 'unreachable' instruction.


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