[llvm] [SimplifyCFG] Use hash map to continue hoisting the common instructions (PR #78615)

[Nikita Popov via llvm-commits]

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@@ -1635,87 +1675,149 @@ 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 BBItrPair = *SuccIterPairBegin++;
+  auto OtherSuccIterPairRange =
+      iterator_range(SuccIterPairBegin, SuccIterPairs.end());
+
+  DenseMap<llvm::hash_code, SmallVector<Instruction *, 2>> OtherSuccessorsHash;
+  DenseMap<Instruction *, unsigned> InstToSkipFlag;
 
+  unsigned skipFlag = 0;
----------------
nikic wrote:

```suggestion
  unsigned SkipFlag = 0;
```
Variables should start with an uppercase letter.

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