Instruction Selection
. straight forward code if efficiency is not an issue
| a=b+c |
Mov b, R 0
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| d=a+e |
Add c, R 0
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Mov R0 , a
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Mov a, R0 |
can be eliminated
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Add e, R0 |
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Mov R 0 , d
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| a=a+1 |
Mov a, R0 |
Inc a
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Add #1, R 0
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Mov R 0, a
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Here is an example of use of instruction selection:
Straight forward code if efficiency is not an issue
| a=b+c |
Mov b, R 0
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| d=a+e |
Add c, R 0
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Mov R0 , a
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Mov a, R0 |
can be eliminated
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Add e, R0 |
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Mov R 0 , d
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| a=a+1 |
Mov a, R0 |
Inc a
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Add #1, R 0
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Mov R 0, a
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Here, "Inc a" takes lesser time as compared to the other set of instructions as others take almost 3 cycles for each instruction but "Inc a" takes only one cycle. Therefore, we should use "Inc a" instruction in place of the other set of instructions.
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