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neg_add
2015 Jun 12
2
[LLVMdev] Prevent instruction selection from clobbering an implicit data dependence through flags?
...o intrinsic calls (i) and (iii), respectively. There are two choices for the instructions in the middle (ii):
1. A verbatim translation into an 'add' and a 'sub' instruction. I prefer this because it does not modify the flags in question.
2. The more idiomatic translation into 'negadd'. In this context, this translation is incorrect because it clobbers the flag and disrupts the data dependence from (i) to (iii).
How can I specify that the second choice is incorrect in this instance because it clobbers the implicit flow.
Thank you,
Nick Johnson
D. E. Shaw Research