[llvm] [AMDGPU][FixIrreducible][UnifyLoopExits] Support callbr with inline-asm (PR #149308)

[Robert Imschweiler via llvm-commits]

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@@ -118,6 +122,34 @@ struct ControlFlowHub {
            std::optional<unsigned> MaxControlFlowBooleans = std::nullopt);
 
   SmallVector<BranchDescriptor> Branches;
+
+  /// \brief Create a new intermediate target block for a callbr edge.
+  ///
+  /// This function creates a new basic block (the "target block") that sits
+  /// between a callbr instruction and one of its successors. The callbr's
+  /// successor is rewired to this new block, and the new block unconditionally
+  /// branches to the original successor. This is useful for normalizing control
+  /// flow, e.g., when transforming irreducible loops.
+  ///
+  /// \param CallBr         The callbr instruction whose edge is to be split.
+  /// \param Succ           The original successor basic block to be reached.
+  /// \param SuccIdx        The index of the successor in the callbr
+  ///                       instruction.
+  /// \param CI             Optional CycleInfo for updating cycle membership.
+  /// \param DTU            Optional DomTreeUpdater for updating the dominator
+  ///                       tree.
+  /// \param LI             Optional LoopInfo for updating loop membership.
+  /// \param UpdatedLI      Optional output flag indicating if LoopInfo has been
+  ///                       updated.
+  ///
+  /// \returns The newly created intermediate target block.
+  ///
+  /// \note This function updates PHI nodes, dominator tree, loop info, and
+  /// cycle info as needed.
+  static BasicBlock *
+  createCallBrTarget(CallBrInst *CallBr, BasicBlock *Succ, unsigned SuccIdx,
+                     CycleInfo *CI = nullptr, DomTreeUpdater *DTU = nullptr,
+                     LoopInfo *LI = nullptr, bool *UpdatedLI = nullptr);
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ro-i wrote:

I'm not sure if the interface is generic enough? It's specifically crafted to add the intermediate callbr target blocks in the context of the control flow hub, where it's important that the cycle and loop info is updated as it's done by `updateCycleLoopInfo`

https://github.com/llvm/llvm-project/pull/149308