Backend: incorrect register allocation

[atirut-w]

This is most likely a fundamental bug with the register allocator and codegen, even more so how they're designed.

The root cause of this issue is that in LLVM, constants with the same type and value have the same pointer, and the allocator uses a map<Value *, reg> to store register allocation information. The allocation algorithm allocates by iterating through instructions in reverse and allocating its operands depending on the opcode. Of course, this means that if there are constants with the same type and value, the old one would be overwritten.

Help needed.

Input:

; int main(int argc, char *argv[])
define i16 @main(i16 %argc, i8** nocapture %argv) {
  %1 = add i16 2, 2
  ret i16 %1
}

Output:

	; Generated by ZDK C Compiler

	.global main
main:
0:
;   %1 = add i16 2, 2
	ld de, 2
	ld de, 2
	add de, de
;   ret i16 %1
	ret

[atirut-w]

Think I figured out a fix now, with the sacrifice being more spilled values.