Instruction Selection for a Simple Virtual Machine

Instruction selection is a crucial step in compiler design, where a high-level operation is translated into a sequence of low-level machine instructions. This challenge asks you to implement a simplified instruction selection algorithm for a very basic virtual machine. You'll be given an expression represented as a sequence of operations and your task is to select appropriate instructions to execute that expression.

Problem Description

You are tasked with building a function selectInstructions that takes an expression represented as a slice of operation strings and returns a slice of instruction strings that can be executed by a simplified virtual machine. The virtual machine has the following operations and corresponding instructions:

• ADD: ADD R1, R2, R3 (Adds the contents of registers R2 and R3 and stores the result in R1)
• SUB: SUB R1, R2, R3 (Subtracts the contents of register R3 from R2 and stores the result in R1)
• MUL: MUL R1, R2, R3 (Multiplies the contents of registers R2 and R3 and stores the result in R1)
• MOV: MOV R1, R2 (Copies the contents of register R2 to register R1)
• LOAD: LOAD R1, value (Loads the given value into register R1)
• STORE: STORE R1, address (Stores the contents of register R1 into the given address)

The input expression is a slice of strings, where each string represents an operation. The operations are always in a valid sequence. You must select instructions that correctly implement the given expression. Assume that registers R1, R2, and R3 are available for use. You can reuse registers as needed. The value in LOAD instructions will be an integer. The address in STORE instructions will be a string.

Examples

Example 1:

Input: ["ADD", "MOV", "SUB"]
Output: ["MOV R1, 1", "ADD R2, R1, R3", "SUB R4, R2, R3"]
Explanation:  We select instructions to perform the operations.  We use R1, R2, R3, and R4 as temporary registers.  We initialize R1 with a value (arbitrarily 1).

Example 2:

Input: ["LOAD", "ADD", "STORE"]
Output: ["LOAD R1, 5", "ADD R2, R1, 10", "STORE R2, 'result'"]
Explanation:  We load 5 into R1, add 10 to it (storing in R2), and then store the result in the address 'result'.

Example 3:

Input: ["MOV", "MUL", "LOAD", "ADD"]
Output: ["MOV R1, R2", "MUL R3, R1, R4", "LOAD R5, 2", "ADD R6, R3, R5"]
Explanation: Demonstrates register reuse and handling of LOAD.

Constraints

• The input slice will contain only the operation names: "ADD", "SUB", "MUL", "MOV", "LOAD", "STORE".
• The length of the input slice will be between 1 and 10, inclusive.
• For LOAD operations, the value will be a positive integer.
• For STORE operations, the address will be a string enclosed in single quotes (e.g., 'result').
• The generated instructions must be valid in the format described above.
• The solution should be reasonably efficient; avoid unnecessary register allocations.

Notes

• You don't need to worry about error handling or invalid input formats (e.g., incorrect operation names). The input will always be valid.
• Focus on correctly translating the operations into instructions.
• You can assume that the virtual machine has enough registers available.
• The register names (R1, R2, R3, etc.) are just placeholders; the specific register names don't matter as long as the instructions are correctly formatted.
• Consider how to reuse registers effectively to minimize the number of instructions generated.
• The order of instructions in the output slice should match the order of operations in the input slice.
• For LOAD instructions, you can choose any positive integer for the value.
• For STORE instructions, you can choose any string for the address.

package main

// selectInstructions takes a slice of operation strings and returns a slice of instruction strings.
func selectInstructions(operations []string) []string {
	instructions := make([]string, 0)
	registerCounter := 1

	for _, op := range operations {
		switch op {
		case "ADD":
			instructions = append(instructions, "ADD R"+string(rune('1'+registerCounter)), "R"+string(rune('1'+registerCounter+1)), "R"+string(rune('1'+registerCounter+2)))
			registerCounter += 3
		case "SUB":
			instructions = append(instructions, "SUB R"+string(rune('1'+registerCounter)), "R"+string(rune('1'+registerCounter+1)), "R"+string(rune('1'+registerCounter+2)))
			registerCounter += 3
		case "MUL":
			instructions = append(instructions, "MUL R"+string(rune('1'+registerCounter)), "R"+string(rune('1'+registerCounter+1)), "R"+string(rune('1'+registerCounter+2)))
			registerCounter += 3
		case "MOV":
			instructions = append(instructions, "MOV R"+string(rune('1'+registerCounter)), "R"+string(rune('1'+registerCounter+1)))
			registerCounter += 2
		case "LOAD":
			instructions = append(instructions, "LOAD R"+string(rune('1'+registerCounter)), "5") // Arbitrary value
			registerCounter++
		case "STORE":
			instructions = append(instructions, "STORE R"+string(rune('1'+registerCounter)), "'result'") // Arbitrary address
			registerCounter++
		}
	}

	return instructions
}