[llvm] [SimplifyCFG] Fix hoisting problem in SimplifyCFG (PR #78615)

[Quentin Dian via llvm-commits]

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@@ -1635,87 +1668,137 @@ bool SimplifyCFGOpt::hoistCommonCodeFromSuccessors(BasicBlock *BB,
   // many instructions we skip, serving as a compilation time control as well as
   // preventing excessive increase of life ranges.
   unsigned NumSkipped = 0;
-  // If we find an unreachable instruction at the beginning of a basic block, we
-  // can still hoist instructions from the rest of the basic blocks.
-  if (SuccIterPairs.size() > 2) {
-    erase_if(SuccIterPairs,
-             [](const auto &Pair) { return isa<UnreachableInst>(Pair.first); });
-    if (SuccIterPairs.size() < 2)
-      return false;
-  }
 
   bool Changed = false;
+  auto *SuccIterPairBegin = SuccIterPairs.begin();
+  SuccIterPairBegin++;
+  auto OtherSuccIterPairRange =
+      iterator_range(SuccIterPairBegin, SuccIterPairs.end());
+  auto OtherSuccIterRange = make_first_range(OtherSuccIterPairRange);
+  using InstrFlagPair = std::pair<Instruction *, unsigned>;
+  SmallVector<DenseMap<llvm::hash_code, InstrFlagPair>, 2> OtherSuccessorsHash;
+
+  for (auto BBItrPair : OtherSuccIterRange) {
+    // Fill the hashmap for every other successor
+    DenseMap<llvm::hash_code, InstrFlagPair> hashMap;
+    unsigned skipFlag = 0;
+    Instruction *I = nullptr;
+    do {
+      I = &*BBItrPair;
+      skipFlag |= skippedInstrFlags(I);
+      hashMap[getHash(I)] = InstrFlagPair(I, skipFlag);
+      BBItrPair++;
+    } while (!I->isTerminator());
+    OtherSuccessorsHash.push_back(hashMap);
+  }
 
+  // Keep track of instructions skipped in the first successor
+  unsigned SkipFlagsBB1 = 0;
+  bool SameLevelHoist = true;
   for (;;) {
     auto *SuccIterPairBegin = SuccIterPairs.begin();
     auto &BB1ItrPair = *SuccIterPairBegin++;
     auto OtherSuccIterPairRange =
         iterator_range(SuccIterPairBegin, SuccIterPairs.end());
-    auto OtherSuccIterRange = make_first_range(OtherSuccIterPairRange);
-
     Instruction *I1 = &*BB1ItrPair.first;
-
+    
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DianQK wrote:

The clang-format did not delete the spaces?

https://github.com/llvm/llvm-project/pull/78615