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253
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1 import logging
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2 from transform import FunctionPass
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3 from ir import *
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4
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5 def isAllocPromotable(allocinst):
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6 # Check if alloc value is only used by load and store operations.
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7 assert type(allocinst) is Alloc
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261
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8 return all(type(use) in [Load, Store] for use in allocinst.value.used_by)
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253
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9
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10 class Mem2RegPromotor(FunctionPass):
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11 def promoteSingleBlock(self, ai):
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12 v = ai.value
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13 bb = ai.Block
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14
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15 # Replace all loads with the value:
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16 loads = [i for i in v.used_by if isinstance(i, Load)]
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17 stores = [i for i in v.used_by if isinstance(i, Store)]
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18 stores.sort(key=lambda s: s.Position)
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19 stores.reverse()
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20
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21 for load in loads:
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22 idx = load.Position
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23 # Search upwards:
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24 for store in stores:
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25 if store.Position < load.Position:
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26 break
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261
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27 load.value.replaceby(store.value)
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253
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28 logging.debug('replaced {} with {}'.format(load, store.value))
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29 bb.removeInstruction(load)
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30
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31 # Remove store instructions:
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32 for store in stores:
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33 sv = store.value
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34 logging.debug('removing {}'.format(store))
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35 bb.removeInstruction(store)
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36 #assert sv.Used
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37
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38 # Remove alloca instruction:
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39 assert not ai.value.Used, ai.value.used_by
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40 bb.removeInstruction(ai)
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41
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42 def promote(self, ai):
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43 # Find load operations and replace them with assignments
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44 v = ai.value
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45 if len(ai.value.UsedInBlocks) == 1:
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46 self.promoteSingleBlock(ai)
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47 return
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48
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49 loads = [i for i in v.used_by if isinstance(i, Load)]
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50 stores = [i for i in v.used_by if isinstance(i, Store)]
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51
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52 # Each store instruction can be removed (later).
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53 # Instead of storing the value, we use it
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54 # where the load would have been!
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55 replMap = {}
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56 for store in stores:
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57 replMap[store] = store.value
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58
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59 # for each load, track back what the defining store
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60 # was.
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61 for load in loads:
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62 pass
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63
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64 def onFunction(self, f):
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65 for bb in f.BasicBlocks:
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66 allocs = [i for i in bb.Instructions if isinstance(i, Alloc)]
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67 for i in allocs:
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68 if isAllocPromotable(i):
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69 self.promote(i)
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70
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