[Sprint3] Alloca2RegPass

[dongjinBaek]

Alloca2RegPass

• changes load/store variables using alloca to reg

  assigning registers

• for alloca variable of length n, replace with n global variables named $reg0, ... $reg(n-1)
• add load $regi 0 instruction.
• this load inst is not actually loaded, and backend will allocate specific register instead

load

• change load instruction using alloca variable by
  • split the block into upper, bottom part of load inst.
  • between splitted block, insert n blocks for switch, which unconditional branch to bottom part is the only instruction
  • replace terminator inst. of upper part to switch inst, which leads to n switch blocks made above
  • insert phinode at the start of the bottom block, so that value is differed by which reg it used
  • replace all uses of load inst to phi node

store

• change store inst similarly with load inst, but with some changes
  • switch block has call inst calling custom $store function
  • this function call will be changed to storing value to register in backend
  • there is no phinode needed