dead_code_elimination_pass: Remove unreachable Phi arguments

src/shader_recompiler/frontend/ir/value.h

@@ -179,9 +179,13 @@ public:
 
     /// Get a pointer to the block of a phi argument.
     [[nodiscard]] Block* PhiBlock(size_t index) const;
+
     /// Add phi operand to a phi instruction.
     void AddPhiOperand(Block* predecessor, const Value& value);
 
+    // Erase the phi operand at the given index.
+    void ErasePhiOperand(size_t index);
+
     /// Orders the Phi arguments from farthest away to nearest.
     void OrderPhiArgs();