[llvm] 192cce1 - Revert "Recommit "[GlobalOpt] Pass DTU to removeUnreachableBlocks instead of recomputing.""

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2020-01-14T14:50:07Z
New Revision: 192cce10f67e4f22be6d9b8c0975f78ad246d1bd

URL: https://github.com/llvm/llvm-project/commit/192cce10f67e4f22be6d9b8c0975f78ad246d1bd
DIFF: https://github.com/llvm/llvm-project/commit/192cce10f67e4f22be6d9b8c0975f78ad246d1bd.diff

LOG: Revert "Recommit "[GlobalOpt] Pass DTU to removeUnreachableBlocks instead of recomputing.""

This reverts commit a03d7b0f24b65d69721dbbbc871df0629efcf774.

As discussed in D68298, this causes a compile-time regression, in case
the DTs requested are not used elsewhere in GlobalOpt. We should only
get the DTs if they are available here, but this seems not possible with
the legacy pass manager from a module pass.

Added: 
    

Modified: 
    llvm/lib/Transforms/IPO/GlobalOpt.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index beb3785eda31..0fd966457ece 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2298,10 +2298,14 @@ OptimizeFunctions(Module &M,
     // So, remove unreachable blocks from the function, because a) there's
     // no point in analyzing them and b) GlobalOpt should otherwise grow
     // some more complicated logic to break these cycles.
+    // Removing unreachable blocks might invalidate the dominator so we
+    // recalculate it.
     if (!F->isDeclaration()) {
-      auto &DT = LookupDomTree(*F);
-      DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
-      Changed |= removeUnreachableBlocks(*F, &DTU);
+      if (removeUnreachableBlocks(*F)) {
+        auto &DT = LookupDomTree(*F);
+        DT.recalculate(*F);
+        Changed = true;
+      }
     }
 
     Changed |= processGlobal(*F, GetTLI, LookupDomTree);