[llvm] [BOLT][AArch64] Implement PLTCall optimization (PR #93584)

[Pavel Samolysov via llvm-commits]

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@@ -1412,9 +1413,15 @@ class MCPlusBuilder {
     return false;
   }
 
-  /// Modify a direct call instruction \p Inst with an indirect call taking
-  /// a destination from a memory location pointed by \p TargetLocation symbol.
-  virtual bool convertCallToIndirectCall(MCInst &Inst,
+  /// Modify a direct call instruction pointed by the iterator \p It, with an
+  /// indirect call taking a destination from a memory location pointed by \p
+  /// TargetLocation symbol. If additional instructions need to be prepended
+  /// before \p It, then the iterator must be updated to point to the indirect
+  /// call instruction.
+  ///
+  /// \return true on success
+  virtual bool convertCallToIndirectCall(BinaryBasicBlock &BB,
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samolisov wrote:

@paschalis-mpeis There is a polymorphic iterator `InstructionIterator`, which is defined in `MCPlusBuilder.h` and there is a pattern to pass every required instruction sequence to `MCPlusBuilder`'s methods by this iterator (but, as I see, it is used to pass a chain of instruction with no modifications of the iterator itself). Also there is the `InstructionListType` and, please have a look at the [`createLoadImmediate`](https://github.com/llvm/llvm-project/blob/main/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp#L1453) for example, the generated in `MCPlusBuilder` instruction list should be returned by value.

https://github.com/llvm/llvm-project/pull/93584