[llvm] [AMDGPU] Add IR LiveReg type-based optimization (PR #66838)

[Matt Arsenault via llvm-commits]

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@@ -81,6 +81,86 @@ class AMDGPULateCodeGenPrepare
   bool visitLoadInst(LoadInst &LI);
 };
 
+class ConversionCandidateInfo {
+private:
+  // The instruction which defined the original virtual register used across
+  // blocks
+  Instruction *LiveRegDef;
+  // The original type
+  Type *OriginalType;
+  // The desired type
+  Type *NewType;
+  // The instruction sequence that converts the virtual register, to be used
+  // instead of the original
+  Instruction *Converted = nullptr;
+  // The builder used to build the conversion instruction
+  IRBuilder<> ConvertBuilder;
+
+public:
+  // The instruction which defined the original virtual register used across
+  // blocks
+  Instruction *getLiveRegDef() { return LiveRegDef; }
+  // The original type
+  Type *getOriginalType() { return OriginalType; }
+  // The desired type
+  Type *getNewType() { return NewType; }
+  void setNewType(Type *NewType) { this->NewType = NewType; }
+  // The instruction that conerts the virtual register, to be used instead of
+  // the original
+  Instruction *getConverted() { return Converted; }
+  void setConverted(Instruction *Converted) { this->Converted = Converted; }
+  // The builder used to build the conversion instruction
+  IRBuilder<> &getConvertBuilder() { return ConvertBuilder; }
+  // Do we have a instruction sequence which convert the original virtual
+  // register
+  bool hasConverted() { return Converted != nullptr; }
+
+  ConversionCandidateInfo(Instruction *LiveRegDef, BasicBlock *InsertBlock,
+                          BasicBlock::iterator InsertPt)
+      : LiveRegDef(LiveRegDef), OriginalType(LiveRegDef->getType()),
+        ConvertBuilder(InsertBlock, InsertPt) {}
+  ConversionCandidateInfo(Instruction *LiveRegDef, Type *NewType,
+                          BasicBlock *InsertBlock,
+                          BasicBlock::iterator InsertPt)
+      : LiveRegDef(LiveRegDef), OriginalType(LiveRegDef->getType()),
+        NewType(NewType), ConvertBuilder(InsertBlock, InsertPt) {}
+};
+
+class LiveRegOptimizer {
+private:
+  Module *Mod = nullptr;
+  // The scalar type to convert to
+  Type *ConvertToScalar;
+  // Holds the collection of PHIs with their pending new operands
+  SmallVector<std::pair<Instruction *,
+                        SmallVector<std::pair<Instruction *, BasicBlock *>, 4>>,
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arsenm wrote:

Use a typedef for these nested types? 

https://github.com/llvm/llvm-project/pull/66838