[llvm] [X86] Don't always seperate conditions in `(br (and/or cond0, cond1))` into seperate branches (PR #81689)

[Simon Pilgrim via llvm-commits]

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@@ -2432,6 +2434,141 @@ SelectionDAGBuilder::EmitBranchForMergedCondition(const Value *Cond,
   SL->SwitchCases.push_back(CB);
 }
 
+// Collect dependings on V recursively. This is used for the cost analysis in
+// `shouldKeepJumpConditionsTogether`.
+static bool
+collectInstructionDeps(SmallPtrSet<const Instruction *, 8> *Deps,
+                       const Value *V,
+                       SmallPtrSet<const Instruction *, 8> *Necessary = nullptr,
+                       unsigned Depth = 0) {
+  // Return false if we have an incomplete count.
+  if (Depth >= SelectionDAG::MaxRecursionDepth)
+    return false;
+
+  auto *I = dyn_cast<Instruction>(V);
+  if (I == nullptr)
+    return true;
+
+  if (Necessary != nullptr) {
+    // This instruction is necessary for the other side of the condition so
+    // don't count it.
+    if (Necessary->contains(I))
+      return true;
+  }
+
+  // Already added this dep.
+  if (!Deps->insert(I).second)
+    return true;
+
+  for (unsigned OpIdx = 0; OpIdx < I->getNumOperands(); ++OpIdx)
----------------
RKSimon wrote:

(style) `for (unsigned OpIdx = 0, E = I->getNumOperands(); OpIdx < E; ++OpIdx)`

https://github.com/llvm/llvm-project/pull/81689