[llvm] [LoopDeletion] Check for uses in unreachable basic blocks even when there is no exit block. (PR #173428)

[Nikita Popov via llvm-commits]

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@@ -608,45 +608,45 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
   llvm::SmallDenseSet<DebugVariable, 4> DeadDebugSet;
   llvm::SmallVector<DbgVariableRecord *, 4> DeadDbgVariableRecords;
 
-  if (ExitBlock) {
-    // Given LCSSA form is satisfied, we should not have users of instructions
-    // within the dead loop outside of the loop. However, LCSSA doesn't take
-    // unreachable uses into account. We handle them here.
-    // We could do it after drop all references (in this case all users in the
-    // loop will be already eliminated and we have less work to do but according
-    // to API doc of User::dropAllReferences only valid operation after dropping
-    // references, is deletion. So let's substitute all usages of
-    // instruction from the loop with poison value of corresponding type first.
-    for (auto *Block : L->blocks())
-      for (Instruction &I : *Block) {
-        auto *Poison = PoisonValue::get(I.getType());
-        for (Use &U : llvm::make_early_inc_range(I.uses())) {
-          if (auto *Usr = dyn_cast<Instruction>(U.getUser()))
-            if (L->contains(Usr->getParent()))
-              continue;
-          // If we have a DT then we can check that uses outside a loop only in
-          // unreachable block.
-          if (DT)
-            assert(!DT->isReachableFromEntry(U) &&
-                   "Unexpected user in reachable block");
-          U.set(Poison);
-        }
-
-        // For one of each variable encountered, preserve a debug record (set
-        // to Poison) and transfer it to the loop exit. This terminates any
-        // variable locations that were set during the loop.
-        for (DbgVariableRecord &DVR :
-             llvm::make_early_inc_range(filterDbgVars(I.getDbgRecordRange()))) {
-          DebugVariable Key(DVR.getVariable(), DVR.getExpression(),
-                            DVR.getDebugLoc().get());
-          if (!DeadDebugSet.insert(Key).second)
+  // Given LCSSA form is satisfied, we should not have users of instructions
+  // within the dead loop outside of the loop. However, LCSSA doesn't take
+  // unreachable uses into account. We handle them here.
+  // We could do it after drop all references (in this case all users in the
+  // loop will be already eliminated and we have less work to do but according
+  // to API doc of User::dropAllReferences only valid operation after dropping
+  // references, is deletion. So let's substitute all usages of
+  // instruction from the loop with poison value of corresponding type first.
+  for (auto *Block : L->blocks())
+    for (Instruction &I : *Block) {
+      auto *Poison = PoisonValue::get(I.getType());
+      for (Use &U : llvm::make_early_inc_range(I.uses())) {
+        if (auto *Usr = dyn_cast<Instruction>(U.getUser()))
+          if (L->contains(Usr->getParent()))
             continue;
-          // Unlinks the DVR from it's container, for later insertion.
-          DVR.removeFromParent();
-          DeadDbgVariableRecords.push_back(&DVR);
-        }
+        // If we have a DT then we can check that uses outside a loop only in
+        // unreachable block.
+        if (DT)
+          assert(!DT->isReachableFromEntry(U) &&
+                 "Unexpected user in reachable block");
+        U.set(Poison);
       }
 
+      // For one of each variable encountered, preserve a debug record (set
+      // to Poison) and transfer it to the loop exit. This terminates any
+      // variable locations that were set during the loop.
+      for (DbgVariableRecord &DVR :
----------------
nikic wrote:

I think this block still needs to be guarded by ExitBlock. Otherwise we'll leak these records? (They get unlinked but not deleted.)

https://github.com/llvm/llvm-project/pull/173428