[llvm] f985356 - [SimplifyCFG] simplifyUnreachable(): switch to non-permissive DomTree updates

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2021-01-06T01:52:36+03:00
New Revision: f98535686e3c1fa76986337639df1636282692c9

URL: https://github.com/llvm/llvm-project/commit/f98535686e3c1fa76986337639df1636282692c9
DIFF: https://github.com/llvm/llvm-project/commit/f98535686e3c1fa76986337639df1636282692c9.diff

LOG: [SimplifyCFG] simplifyUnreachable(): switch to non-permissive DomTree updates

... which requires not removing a DomTree edge if the switch's default
still points at that destination, because it can't be removed;
... and not processing the same predecessor more than once.

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SimplifyCFG.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 9f808278d899..d01d9512212c 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4616,7 +4616,6 @@ bool SimplifyCFGOpt::simplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
   return false;
 }
 
-// FIXME: switch to non-permissive DomTreeUpdater::applyUpdates().
 bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
   BasicBlock *BB = UI->getParent();
 
@@ -4678,7 +4677,7 @@ bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
 
   std::vector<DominatorTree::UpdateType> Updates;
 
-  SmallVector<BasicBlock *, 8> Preds(predecessors(BB));
+  SmallSetVector<BasicBlock *, 8> Preds(pred_begin(BB), pred_end(BB));
   for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
     auto *Predecessor = Preds[i];
     Instruction *TI = Predecessor->getTerminator();
@@ -4718,7 +4717,9 @@ bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
         e = SU->case_end();
         Changed = true;
       }
-      Updates.push_back({DominatorTree::Delete, Predecessor, BB});
+      // Note that the default destination can't be removed!
+      if (SI->getDefaultDest() != BB)
+        Updates.push_back({DominatorTree::Delete, Predecessor, BB});
     } else if (auto *II = dyn_cast<InvokeInst>(TI)) {
       if (II->getUnwindDest() == BB) {
         if (DTU)
@@ -4785,7 +4786,7 @@ bool SimplifyCFGOpt::simplifyUnreachable(UnreachableInst *UI) {
   }
 
   if (DTU)
-    DTU->applyUpdatesPermissive(Updates);
+    DTU->applyUpdates(Updates);
 
   // If this block is now dead, remove it.
   if (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()) {